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From mwa...@apache.org
Subject [11/13] accumulo-website git commit: Jekyll build from master:7cc70b2
Date Mon, 22 May 2017 17:31:58 GMT
http://git-wip-us.apache.org/repos/asf/accumulo-website/blob/7b2eb317/docs/unreleased/administration/fate.html
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diff --git a/docs/unreleased/administration/fate.html b/docs/unreleased/administration/fate.html
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+<!DOCTYPE html>
+<html lang="en">
+<head>
+<!--
+    Licensed to the Apache Software Foundation (ASF) under one or more
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+
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+
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+<link rel="stylesheet" type="text/css" href="https://cdn.datatables.net/v/bs/jq-2.2.3/dt-1.10.12/datatables.min.css">
+<link href="/css/accumulo.css" rel="stylesheet" type="text/css">
+
+<title>Accumulo Documentation - FATE</title>
+
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+<script type="text/javascript" src="https://cdn.datatables.net/v/bs/jq-2.2.3/dt-1.10.12/datatables.min.js"></script>
+<script>
+  // show location of canonical site if not currently on the canonical site
+  $(function() {
+    var host = window.location.host;
+    if (typeof host !== 'undefined' && host !== 'accumulo.apache.org') {
+      $('#non-canonical').show();
+    }
+  });
+
+  $(function() {
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+        </div>
+        <div id="content">
+          
+          <div class="alert alert-danger" role="alert">This documentation is for an unreleased version of Apache Accumulo that is currently under development! Check out the <a href="/docs-1.8/">documentation for the latest release</a>.</div>
+
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+                
+              </div>
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+              <div class="panel-body">
+                
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/development/iterator_design">Iterator Design</a></div>
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/development/iterator_testing">Iterator Testing</a></div>
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/development/development_tools">Development Tools</a></div>
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/development/sampling">Sampling</a></div>
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/development/summaries">Summary Statistics</a></div>
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/development/security">Security</a></div>
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/development/high_speed_ingest">High-Speed Ingest</a></div>
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/development/analytics">Analytics</a></div>
+                
+              </div>
+            </div>
+          
+        
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+        
+          
+        
+          
+        
+      
+        
+          
+            <div class="panel-heading" role="tab" id="headingOne">
+              <h4 class="panel-title">
+                <a role="button" data-toggle="collapse" data-parent="#accordion" href="#collapseadministration" aria-expanded="true" aria-controls="collapseadministration">
+                  Administration
+                </a>
+              </h4>
+            </div>
+            <div id="collapseadministration" class="panel-collapse collapse in" role="tabpanel" aria-labelledby="headingOne">
+              <div class="panel-body">
+                
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/administration/overview">Overview</a></div>
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/administration/configuration-management">Configuration Management</a></div>
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/administration/configuration-properties">Configuration Properties</a></div>
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/administration/kerberos">Kerberos</a></div>
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/administration/replication">Replication</a></div>
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/administration/fate">FATE</a></div>
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/administration/multivolume">Multi-Volume Installations</a></div>
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/administration/ssl">SSL</a></div>
+                
+              </div>
+            </div>
+          
+        
+          
+        
+          
+        
+          
+        
+          
+        
+      
+        
+          
+        
+          
+        
+          
+        
+          
+        
+          
+            <div class="panel-heading" role="tab" id="headingOne">
+              <h4 class="panel-title">
+                <a role="button" data-toggle="collapse" data-parent="#accordion" href="#collapsetroubleshooting" aria-expanded="false" aria-controls="collapsetroubleshooting">
+                  Troubleshooting
+                </a>
+              </h4>
+            </div>
+            <div id="collapsetroubleshooting" class="panel-collapse collapse" role="tabpanel" aria-labelledby="headingOne">
+              <div class="panel-body">
+                
+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/troubleshooting/overview">Overview</a></div>
+                
+              </div>
+            </div>
+          
+        
+      
+      </div>
+    </div>
+  </div>
+  <div class="col-md-9">
+    
+    <p><a href="/docs/unreleased/">Accumulo unreleased docs</a> &nbsp;&gt;&gt;&nbsp; Administration &nbsp;&gt;&gt;&nbsp; FATE</p>
+    
+    
+    <h1>FATE</h1>
+    
+    <p>Accumulo must implement a number of distributed, multi-step operations to support
+the client API. Creating a new table is a simple example of an atomic client call
+which requires multiple steps in the implementation: get a unique table ID, configure
+default table permissions, populate information in ZooKeeper to record the table’s
+existence, create directories in HDFS for the table’s data, etc. Implementing these
+steps in a way that is tolerant to node failure and other concurrent operations is
+very difficult to achieve. Accumulo includes a Fault-Tolerant Executor (FATE) which
+is widely used server-side to implement the client API safely and correctly.</p>
+
+<p>Fault-Tolerant Executor (FATE) is the implementation detail which ensures that tables in creation when the
+Master dies will be successfully created when another Master process is started.
+This alleviates the need for any external tools to correct some bad state – Accumulo can
+undo the failure and self-heal without any external intervention.</p>
+
+<h2 id="overview">Overview</h2>
+
+<p>FATE consists of two primary components: a repeatable, persisted operation (REPO), a storage
+layer for REPOs and an execution system to run REPOs. Accumulo uses ZooKeeper as the storage
+layer for FATE and the Accumulo Master acts as the execution system to run REPOs.</p>
+
+<p>The important characteristic of REPOs are that they implemented in a way that is idempotent:
+every operation must be able to undo or replay a partial execution of itself. Requiring the
+implementation of the operation to support this functional greatly simplifies the execution
+of these operations. This property is also what guarantees safety in light of failure conditions.</p>
+
+<h2 id="administration">Administration</h2>
+
+<p>Sometimes, it is useful to inspect the current FATE operations, both pending and executing.
+For example, a command that is not completing could be blocked on the execution of another
+operation. Accumulo provides an Accumulo shell command to interact with fate.</p>
+
+<p>The <code class="highlighter-rouge">fate</code> shell command accepts a number of arguments for different functionality:
+<code class="highlighter-rouge">list</code>/<code class="highlighter-rouge">print</code>, <code class="highlighter-rouge">fail</code>, <code class="highlighter-rouge">delete</code>, <code class="highlighter-rouge">dump</code>.</p>
+
+<h3 id="listprint">List/Print</h3>
+
+<p>Without any additional arguments, this command will print all operations that still exist in
+the FATE store (ZooKeeper). This will include active, pending, and completed operations (completed
+operations are lazily removed from the store). Each operation includes a unique “transaction ID”, the
+state of the operation (e.g. <code class="highlighter-rouge">NEW</code>, <code class="highlighter-rouge">IN_PROGRESS</code>, <code class="highlighter-rouge">FAILED</code>), any locks the
+transaction actively holds and any locks it is waiting to acquire.</p>
+
+<p>This option can also accept transaction IDs which will restrict the list of transactions shown.</p>
+
+<h3 id="fail">Fail</h3>
+
+<p>This command can be used to manually fail a FATE transaction and requires a transaction ID
+as an argument. Failing an operation is not a normal procedure and should only be performed
+by an administrator who understands the implications of why they are failing the operation.</p>
+
+<h3 id="delete">Delete</h3>
+
+<p>This command requires a transaction ID and will delete any locks that the transaction
+holds. Like the fail command, this command should only be used in extreme circumstances
+by an administrator that understands the implications of the command they are about to
+invoke. It is not normal to invoke this command.</p>
+
+<h3 id="dump">Dump</h3>
+
+<p>This command accepts zero more transaction IDs.  If given no transaction IDs,
+it will dump all active transactions.  A FATE operations is compromised as a
+sequence of REPOs.  In order to start a FATE transaction, a REPO is pushed onto
+a per transaction REPO stack.  The top of the stack always contains the next
+REPO the FATE transaction should execute.  When a REPO is successful it may
+return another REPO which is pushed on the stack.  The <code class="highlighter-rouge">dump</code> command will
+print all of the REPOs on each transactions stack.  The REPOs are serialized to
+JSON in order to make them human readable.</p>
+
+  </div>
+</div>
+
+        </div>
+
+        
+<footer>
+
+  <p><a href="https://www.apache.org/foundation/contributing"><img src="https://www.apache.org/images/SupportApache-small.png" alt="Support the ASF" id="asf-logo" height="100" /></a></p>
+
+  <p>Copyright © 2011-2017 The Apache Software Foundation. Licensed under the <a href="https://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
+
+</footer>
+
+
+      </div>
+    </div>
+  </div>
+</body>
+</html>

http://git-wip-us.apache.org/repos/asf/accumulo-website/blob/7b2eb317/docs/unreleased/administration/kerberos.html
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diff --git a/docs/unreleased/administration/kerberos.html b/docs/unreleased/administration/kerberos.html
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+<!DOCTYPE html>
+<html lang="en">
+<head>
+<!--
+    Licensed to the Apache Software Foundation (ASF) under one or more
+    contributor license agreements.  See the NOTICE file distributed with
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+    (the "License"); you may not use this file except in compliance with
+    the License.  You may obtain a copy of the License at
+
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+
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+<link href="//netdna.bootstrapcdn.com/font-awesome/4.0.3/css/font-awesome.css" rel="stylesheet">
+<link rel="stylesheet" type="text/css" href="https://cdn.datatables.net/v/bs/jq-2.2.3/dt-1.10.12/datatables.min.css">
+<link href="/css/accumulo.css" rel="stylesheet" type="text/css">
+
+<title>Accumulo Documentation - Kerberos</title>
+
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+<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>
+<script type="text/javascript" src="https://cdn.datatables.net/v/bs/jq-2.2.3/dt-1.10.12/datatables.min.js"></script>
+<script>
+  // show location of canonical site if not currently on the canonical site
+  $(function() {
+    var host = window.location.host;
+    if (typeof host !== 'undefined' && host !== 'accumulo.apache.org') {
+      $('#non-canonical').show();
+    }
+  });
+
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+                
+                <div class="row doc-sidebar-link"><a href="/docs/unreleased/administration/configuration-properties">Configuration Properties</a></div>
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+                
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+                
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+                
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+                  Troubleshooting
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+              </h4>
+            </div>
+            <div id="collapsetroubleshooting" class="panel-collapse collapse" role="tabpanel" aria-labelledby="headingOne">
+              <div class="panel-body">
+                
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+    </div>
+  </div>
+  <div class="col-md-9">
+    
+    <p><a href="/docs/unreleased/">Accumulo unreleased docs</a> &nbsp;&gt;&gt;&nbsp; Administration &nbsp;&gt;&gt;&nbsp; Kerberos</p>
+    
+    
+    <h1>Kerberos</h1>
+    
+    <h2 id="overview">Overview</h2>
+
+<p>Kerberos is a network authentication protocol that provides a secure way for
+peers to prove their identity over an unsecure network in a client-server model.
+A centralized key-distribution center (KDC) is the service that coordinates
+authentication between a client and a server. Clients and servers use “tickets”,
+obtained from the KDC via a password or a special file called a “keytab”, to
+communicate with the KDC and prove their identity. A KDC administrator must
+create the principal (name for the client/server identiy) and the password
+or keytab, securely passing the necessary information to the actual user/service.
+Properly securing the KDC and generated ticket material is central to the security
+model and is mentioned only as a warning to administrators running their own KDC.</p>
+
+<p>To interact with Kerberos programmatically, GSSAPI and SASL are two standards
+which allow cross-language integration with Kerberos for authentication. GSSAPI,
+the generic security service application program interface, is a standard which
+Kerberos implements. In the Java programming language, the language itself also implements
+GSSAPI which is leveraged by other applications, like Apache Hadoop and Apache Thrift.
+SASL, simple authentication and security layer, is a framework for authentication and
+and security over the network. SASL provides a number of mechanisms for authentication,
+one of which is GSSAPI. Thus, SASL provides the transport which authenticates
+using GSSAPI that Kerberos implements.</p>
+
+<p>Kerberos is a very complicated software application and is deserving of much
+more description than can be provided here. An <a href="http://www.roguelynn.com/words/explain-like-im-5-kerberos/">explain like I`m 5</a>
+blog post is very good at distilling the basics, while <a href="http://web.mit.edu/kerberos/">MIT Keberos’s project page</a>
+contains lots of documentation for users or administrators. Various Hadoop “vendors”
+also provide free documentation that includes step-by-step instructions for
+configuring Hadoop and ZooKeeper (which will be henceforth considered as prerequisites).</p>
+
+<h2 id="within-hadoop">Within Hadoop</h2>
+
+<p>Out of the box, HDFS and YARN have no ability to enforce that a user is who
+they claim they are. Thus, any basic Hadoop installation should be treated as
+unsecure: any user with access to the cluster has the ability to access any data.
+Using Kerberos to provide authentication, users can be strongly identified, delegating
+to Kerberos to determine who a user is and enforce that a user is who they claim to be.
+As such, Kerberos is widely used across the entire Hadoop ecosystem for strong
+authentication. Since server processes accessing HDFS or YARN are required
+to use Kerberos to authenticate with HDFS, it makes sense that they also require
+Kerberos authentication from their clients, in addition to other features provided
+by SASL.</p>
+
+<p>A typical deployment involves the creation of Kerberos principals for all server
+processes (Hadoop datanodes and namenode(s), ZooKeepers), the creation of a keytab
+file for each principal and then proper configuration for the Hadoop site xml files.
+Users also need Kerberos principals created for them; however, a user typically
+uses a password to identify themselves instead of a keytab. Users can obtain a
+ticket granting ticket (TGT) from the KDC using their password which allows them
+to authenticate for the lifetime of the TGT (typically one day by default) and alleviates
+the need for further password authentication.</p>
+
+<p>For client server applications, like web servers, a keytab can be created which
+allow for fully-automated Kerberos identification removing the need to enter any
+password, at the cost of needing to protect the keytab file. These principals
+will apply directly to authentication for clients accessing Accumulo and the
+Accumulo processes accessing HDFS.</p>
+
+<h2 id="delegation-tokens">Delegation Tokens</h2>
+
+<p>MapReduce, a common way that clients interact with Accumulo, does not map well to the
+client-server model that Kerberos was originally designed to support. Specifically, the parallelization
+of tasks across many nodes introduces the problem of securely sharing the user credentials across
+these tasks in as safe a manner as possible. To address this problem, Hadoop introduced the notion
+of a delegation token to be used in distributed execution settings.</p>
+
+<p>A delegation token is nothing more than a short-term, on-the-fly password generated after authenticating with the user’s
+credentials.  In Hadoop itself, the Namenode and ResourceManager, for HDFS and YARN respectively, act as the gateway for
+delegation tokens requests. For example, before a YARN job is submitted, the implementation will request delegation
+tokens from the NameNode and ResourceManager so the YARN tasks can communicate with HDFS and YARN. In the same manner,
+support has been added in the Accumulo Master to generate delegation tokens to enable interaction with Accumulo via
+MapReduce when Kerberos authentication is enabled in a manner similar to HDFS and YARN.</p>
+
+<p>Generating an expiring password is, arguably, more secure than distributing the user’s
+credentials across the cluster as only access to HDFS, YARN and Accumulo would be
+compromised in the case of the token being compromised as opposed to the entire
+Kerberos credential. Additional details for clients and servers will be covered
+in subsequent sections.</p>
+
+<h2 id="configuring-accumulo">Configuring Accumulo</h2>
+
+<p>To configure Accumulo for use with Kerberos, both client-facing and server-facing
+changes must be made for a functional system on secured Hadoop. As previously mentioned,
+numerous guidelines already exist on the subject of configuring Hadoop and ZooKeeper for
+use with Kerberos and won’t be covered here. It is assumed that you have functional
+Hadoop and ZooKeeper already installed.</p>
+
+<p>Note that on an existing cluster the server side changes will require a full cluster shutdown and restart. You should
+wait to restart the TraceServers until after you’ve completed the rest of the cluster set up and provisioned
+a trace user with appropriate permissions.</p>
+
+<h3 id="servers">Servers</h3>
+
+<p>The first step is to obtain a Kerberos identity for the Accumulo server processes.
+When running Accumulo with Kerberos enabled, a valid Kerberos identity will be required
+to initiate any RPC between Accumulo processes (e.g. Master and TabletServer) in addition
+to any HDFS action (e.g. client to HDFS or TabletServer to HDFS).</p>
+
+<h4 id="generate-principal-and-keytab">Generate Principal and Keytab</h4>
+
+<p>In the <code class="highlighter-rouge">kadmin.local</code> shell or using the <code class="highlighter-rouge">-q</code> option on <code class="highlighter-rouge">kadmin.local</code>, create a
+principal for Accumulo for all hosts that are running Accumulo processes. A Kerberos
+principal is of the form “primary/instance@REALM”. “accumulo” is commonly the “primary”
+(although not required) and the “instance” is the fully-qualified domain name for
+the host that will be running the Accumulo process – this is required.</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>kadmin.local -q "addprinc -randkey accumulo/host.domain.com"
+</code></pre>
+</div>
+
+<p>Perform the above for each node running Accumulo processes in the instance, modifying
+“host.domain.com” for your network. The <code class="highlighter-rouge">randkey</code> option generates a random password
+because we will use a keytab for authentication, not a password, since the Accumulo
+server processes don’t have an interactive console to enter a password into.</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>kadmin.local -q "xst -k accumulo.hostname.keytab accumulo/host.domain.com"
+</code></pre>
+</div>
+
+<p>To simplify deployments, at thet cost of security, all Accumulo principals could
+be globbed into a single keytab</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>kadmin.local -q "xst -k accumulo.service.keytab -glob accumulo*"
+</code></pre>
+</div>
+
+<p>To ensure that the SASL handshake can occur from clients to servers and servers to servers,
+all Accumulo servers must share the same instance and realm principal components as the
+“client” needs to know these to set up the connection with the “server”.</p>
+
+<h4 id="server-configuration">Server Configuration</h4>
+
+<p>A number of properties need to be changed to account to properly configure servers
+in <code class="highlighter-rouge">accumulo-site.xml</code>.</p>
+
+<table>
+  <thead>
+    <tr>
+      <th>Key</th>
+      <th>Default Value</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td>general.kerberos.keytab</td>
+      <td>/etc/security/keytabs/accumulo.service.keytab</td>
+      <td>The path to the keytab for Accumulo on local filesystem. Change the value to the actual path on your system.</td>
+    </tr>
+    <tr>
+      <td>general.kerberos.principal</td>
+      <td>accumulo/_HOST@REALM</td>
+      <td>The Kerberos principal for Accumulo, needs to match the keytab. “_HOST” can be used instead of the actual hostname in the principal and will be automatically expanded to the current FQDN which reduces the configuration file burden.</td>
+    </tr>
+    <tr>
+      <td>instance.rpc.sasl.enabled</td>
+      <td>true</td>
+      <td>Enables SASL for the Thrift Servers (supports GSSAPI)</td>
+    </tr>
+    <tr>
+      <td>rpc.sasl.qop</td>
+      <td>auth</td>
+      <td>One of “auth”, “auth-int”, or “auth-conf”. These map to the SASL defined properties for quality of protection. “auth” is authentication only. “auth-int” is authentication and data integrity. “auth-conf” is authentication, data integrity and confidentiality.</td>
+    </tr>
+    <tr>
+      <td>instance.security.authenticator</td>
+      <td>org.apache.accumulo.server.security.handler.KerberosAuthenticator</td>
+      <td>Configures Accumulo to use the Kerberos principal as the Accumulo username/principal</td>
+    </tr>
+    <tr>
+      <td>instance.security.authorizor</td>
+      <td>org.apache.accumulo.server.security.handler.KerberosAuthorizor</td>
+      <td>Configures Accumulo to use the Kerberos principal for authorization purposes</td>
+    </tr>
+    <tr>
+      <td>instance.security.permissionHandler</td>
+      <td>org.apache.accumulo.server.security.handler.KerberosPermissionHandler</td>
+      <td>Configures Accumulo to use the Kerberos principal for permission purposes</td>
+    </tr>
+    <tr>
+      <td>trace.token.type</td>
+      <td>org.apache.accumulo.core.client.security.tokens.KerberosToken</td>
+      <td>Configures the Accumulo Tracer to use the KerberosToken for authentication when serializing traces to the trace table.</td>
+    </tr>
+    <tr>
+      <td>trace.user</td>
+      <td>accumulo/_HOST@REALM</td>
+      <td>The tracer process needs valid credentials to serialize traces to Accumulo. While the other server processes are creating a SystemToken from the provided keytab and principal, we can still use a normal KerberosToken and the same keytab/principal to serialize traces. Like non-Kerberized instances, the table must be created and permissions granted to the trace.user. The same <code class="highlighter-rouge">_HOST</code> replacement is performed on this value, substituted the FQDN for <code class="highlighter-rouge">_HOST</code>.</td>
+    </tr>
+    <tr>
+      <td>trace.token.property.keytab</td>
+      <td> </td>
+      <td>You can optionally specify the path to a keytab file for the principal given in the <code class="highlighter-rouge">trace.user</code> property. If you don’t set this path, it will default to the value given in <code class="highlighter-rouge">general.kerberos.principal</code>.</td>
+    </tr>
+    <tr>
+      <td>general.delegation.token.lifetime</td>
+      <td>7d</td>
+      <td>The length of time that the server-side secret used to create delegation tokens is valid. After a server-side secret expires, a delegation token created with that secret is no longer valid.</td>
+    </tr>
+    <tr>
+      <td>general.delegation.token.update.interval</td>
+      <td>1d</td>
+      <td>The frequency in which new server-side secrets should be generated to create delegation tokens for clients. Generating new secrets reduces the likelihood of cryptographic attacks.</td>
+    </tr>
+  </tbody>
+</table>
+
+<p>Although it should be a prerequisite, it is ever important that you have DNS properly
+configured for your nodes and that Accumulo is configured to use the FQDN. It
+is extremely important to use the FQDN in each of the “hosts” files for each
+Accumulo process: <code class="highlighter-rouge">masters</code>, <code class="highlighter-rouge">monitors</code>, <code class="highlighter-rouge">tservers</code>, <code class="highlighter-rouge">tracers</code>, and <code class="highlighter-rouge">gc</code>.</p>
+
+<p>Normally, no changes are needed in <code class="highlighter-rouge">accumulo-env.sh</code> to enable Kerberos. Typically, the <code class="highlighter-rouge">krb5.conf</code>
+is installed on the local machine in <code class="highlighter-rouge">/etc/</code>, and the Java library implementations will look
+here to find the necessary configuration to communicate with the KDC. Some installations
+may require a different <code class="highlighter-rouge">krb5.conf</code> to be used for Accumulo which can be accomplished 
+by adding the JVM system property <code class="highlighter-rouge">-Djava.security.krb5.conf=/path/to/other/krb5.conf</code> to
+<code class="highlighter-rouge">JAVA_OPTS</code> in <code class="highlighter-rouge">accumulo-env.sh</code>.</p>
+
+<h4 id="kerberosauthenticator">KerberosAuthenticator</h4>
+
+<p>The <code class="highlighter-rouge">KerberosAuthenticator</code> is an implementation of the pluggable security interfaces
+that Accumulo provides. It builds on top of what the default ZooKeeper-based implementation,
+but removes the need to create user accounts with passwords in Accumulo for clients. As
+long as a client has a valid Kerberos identity, they can connect to and interact with
+Accumulo, but without any permissions (e.g. cannot create tables or write data). Leveraging
+ZooKeeper removes the need to change the permission handler and authorizor, so other Accumulo
+functions regarding permissions and cell-level authorizations do not change.</p>
+
+<p>It is extremely important to note that, while user operations like <code class="highlighter-rouge">SecurityOperations.listLocalUsers()</code>,
+<code class="highlighter-rouge">SecurityOperations.dropLocalUser()</code>, and <code class="highlighter-rouge">SecurityOperations.createLocalUser()</code> will not return
+errors, these methods are not equivalent to normal installations, as they will only operate on
+users which have, at one point in time, authenticated with Accumulo using their Kerberos identity.
+The KDC is still the authoritative entity for user management. The previously mentioned methods
+are provided as they simplify management of users within Accumulo, especially with respect
+to granting Authorizations and Permissions to new users.</p>
+
+<h4 id="administrative-user">Administrative User</h4>
+
+<p>Out of the box (without Kerberos enabled), Accumulo has a single user with administrative permissions “root”.
+This users is used to “bootstrap” other users, creating less-privileged users for applications using
+the system. In Kerberos, to authenticate with the system, it’s required that the client presents Kerberos
+credentials for the principal (user) the client is trying to authenticate as.</p>
+
+<p>Because of this, an administrative user named “root” would be useless in an instance using Kerberos,
+because it is very unlikely to have Kerberos credentials for a principal named <code class="highlighter-rouge">root</code>. When Kerberos is
+enabled, Accumulo will prompt for the name of a user to grant the same permissions as what the <code class="highlighter-rouge">root</code>
+user would normally have. The name of the Accumulo user to grant administrative permissions to can
+also be given by the <code class="highlighter-rouge">-u</code> or <code class="highlighter-rouge">--user</code> options.</p>
+
+<p>If you are enabling Kerberos on an existing cluster, you will need to reinitialize the security system in
+order to replace the existing “root” user with one that can be used with Kerberos. These steps should be
+completed after you have done the previously described configuration changes and will require access to
+a complete <code class="highlighter-rouge">accumulo-site.xml</code>, including the instance secret. Note that this process will delete all
+existing users in the system; you will need to reassign user permissions based on Kerberos principals.</p>
+
+<ol>
+  <li>Ensure Accumulo is not running.</li>
+  <li>Given the path to a <code class="highlighter-rouge">accumulo-site.xml</code> with the instance secret, run the security reset tool. If you are
+prompted for a password you can just hit return, since it won’t be used.</li>
+  <li>Start the Accumulo cluster</li>
+</ol>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>$ accumulo-cluster stop
+...
+$ accumulo init --reset-security
+Running against secured HDFS
+Principal (user) to grant administrative privileges to : acculumo_admin@EXAMPLE.COM
+Enter initial password for accumulo_admin@EXAMPLE.COM (this may not be applicable for your security setup):
+Confirm initial password for accumulo_admin@EXAMPLE.COM:
+$ accumulo-cluster start
+...
+</code></pre>
+</div>
+
+<h4 id="verifying-secure-access">Verifying secure access</h4>
+
+<p>To verify that servers have correctly started with Kerberos enabled, ensure that the processes
+are actually running (they should exit immediately if login fails) and verify that you see
+something similar to the following in the application log.</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>2015-01-07 11:57:56,826 [security.SecurityUtil] INFO : Attempting to login with keytab as accumulo/hostname@EXAMPLE.COM
+2015-01-07 11:57:56,830 [security.UserGroupInformation] INFO : Login successful for user accumulo/hostname@EXAMPLE.COM using keytab file /etc/security/keytabs/accumulo.service.keytab
+</code></pre>
+</div>
+
+<h4 id="impersonation">Impersonation</h4>
+
+<p>Impersonation is functionality which allows a certain user to act as another. One direct application
+of this concept within Accumulo is the Thrift proxy. The Thrift proxy is configured to accept
+user requests and pass them onto Accumulo, enabling client access to Accumulo via any thrift-compatible
+language. When the proxy is running with SASL transports, this enforces that clients present a valid
+Kerberos identity to make a connection. In this situation, the Thrift proxy server does not have
+access to the secret key material in order to make a secure connection to Accumulo as the client,
+it can only connect to Accumulo as itself. Impersonation, in this context, refers to the ability
+of the proxy to authenticate to Accumulo as itself, but act on behalf of an Accumulo user.</p>
+
+<p>Accumulo supports basic impersonation of end-users by a third party via static rules in Accumulo’s
+site configuration file. These two properties are semi-colon separated properties which are aligned
+by index. This first element in the user impersonation property value matches the first element
+in the host impersonation property value, etc.</p>
+
+<div class="language-xml highlighter-rouge"><pre class="highlight"><code><span class="nt">&lt;property&gt;</span>
+  <span class="nt">&lt;name&gt;</span>instance.rpc.sasl.allowed.user.impersonation<span class="nt">&lt;/name&gt;</span>
+  <span class="nt">&lt;value&gt;</span>$PROXY_USER:*<span class="nt">&lt;/value&gt;</span>
+<span class="nt">&lt;/property&gt;</span>
+
+<span class="nt">&lt;property&gt;</span>
+  <span class="nt">&lt;name&gt;</span>instance.rpc.sasl.allowed.host.impersonation<span class="nt">&lt;/name&gt;</span>
+  <span class="nt">&lt;value&gt;</span>*<span class="nt">&lt;/value&gt;</span>
+<span class="nt">&lt;/property&gt;</span>
+</code></pre>
+</div>
+
+<p>Here, <code class="highlighter-rouge">$PROXY_USER</code> can impersonate any user from any host.</p>
+
+<p>The following is an example of specifying a subset of users <code class="highlighter-rouge">$PROXY_USER</code> can impersonate and also
+limiting the hosts from which <code class="highlighter-rouge">$PROXY_USER</code> can initiate requests from.</p>
+
+<div class="language-xml highlighter-rouge"><pre class="highlight"><code><span class="nt">&lt;property&gt;</span>
+  <span class="nt">&lt;name&gt;</span>instance.rpc.sasl.allowed.user.impersonation<span class="nt">&lt;/name&gt;</span>
+  <span class="nt">&lt;value&gt;</span>$PROXY_USER:user1,user2;$PROXY_USER2:user2,user4<span class="nt">&lt;/value&gt;</span>
+<span class="nt">&lt;/property&gt;</span>
+
+<span class="nt">&lt;property&gt;</span>
+  <span class="nt">&lt;name&gt;</span>instance.rpc.sasl.allowed.host.impersonation<span class="nt">&lt;/name&gt;</span>
+  <span class="nt">&lt;value&gt;</span>host1.domain.com,host2.domain.com;*<span class="nt">&lt;/value&gt;</span>
+<span class="nt">&lt;/property&gt;</span>
+</code></pre>
+</div>
+
+<p>Here, <code class="highlighter-rouge">$PROXY_USER</code> can impersonate user1 and user2 only from host1.domain.com or host2.domain.com.
+<code class="highlighter-rouge">$PROXY_USER2</code> can impersonate user2 and user4 from any host.</p>
+
+<p>In these examples, the value <code class="highlighter-rouge">$PROXY_USER</code> is the Kerberos principal of the server which is acting on behalf of a user.
+Impersonation is enforced by the Kerberos principal and the host from which the RPC originated (from the perspective
+of the Accumulo TabletServers/Masters). An asterisk (*) can be used to specify all users or all hosts (depending on the context).</p>
+
+<h4 id="delegation-tokens-1">Delegation Tokens</h4>
+
+<p>Within Accumulo services, the primary task to implement delegation tokens is the generation and distribution
+of a shared secret among all Accumulo tabletservers and the master. The secret key allows for generation
+of delegation tokens for users and verification of delegation tokens presented by clients. If a server
+process is unaware of the secret key used to create a delegation token, the client cannot be authenticated.
+As ZooKeeper distribution is an asynchronous operation (typically on the order of seconds), the
+value for <code class="highlighter-rouge">general.delegation.token.update.interval</code> should be on the order of hours to days to reduce the
+likelihood of servers rejecting valid clients because the server did not yet see a new secret key.</p>
+
+<p>Supporting authentication with both Kerberos credentials and delegation tokens, the SASL thrift
+server accepts connections with either <code class="highlighter-rouge">GSSAPI</code> and <code class="highlighter-rouge">DIGEST-MD5</code> mechanisms set. The <code class="highlighter-rouge">DIGEST-MD5</code> mechanism
+enables authentication as a normal username and password exchange which <code class="highlighter-rouge">DelegationToken</code>s leverages.</p>
+
+<p>Since delegation tokens are a weaker form of authentication than Kerberos credentials, user access
+to obtain delegation tokens from Accumulo is protected with the <code class="highlighter-rouge">DELEGATION_TOKEN</code> system permission. Only
+users with the system permission are allowed to obtain delegation tokens. It is also recommended
+to configure confidentiality with SASL, using the <code class="highlighter-rouge">rpc.sasl.qop=auth-conf</code> configuration property, to
+ensure that prying eyes cannot view the <code class="highlighter-rouge">DelegationToken</code> as it passes over the network.</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code># Check a user's permissions
+admin@REALM@accumulo&gt; userpermissions -u user@REALM
+
+# Grant the DELEGATION_TOKEN system permission to a user
+admin@REALM@accumulo&gt; grant System.DELEGATION_TOKEN -s -u user@REALM
+</code></pre>
+</div>
+
+<h3 id="clients">Clients</h3>
+
+<h4 id="create-client-principal">Create client principal</h4>
+
+<p>Like the Accumulo servers, clients must also have a Kerberos principal created for them. The
+primary difference between a server principal is that principals for users are created
+with a password and also not qualified to a specific instance (host).</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>kadmin.local -q "addprinc $user"
+</code></pre>
+</div>
+
+<p>The above will prompt for a password for that user which will be used to identify that $user.
+The user can verify that they can authenticate with the KDC using the command <code class="highlighter-rouge">kinit $user</code>.
+Upon entering the correct password, a local credentials cache will be made which can be used
+to authenticate with Accumulo, access HDFS, etc.</p>
+
+<p>The user can verify the state of their local credentials cache by using the command <code class="highlighter-rouge">klist</code>.</p>
+
+<div class="language-shell highlighter-rouge"><pre class="highlight"><code><span class="gp">$ </span>klist
+Ticket cache: FILE:/tmp/krb5cc_123
+Default principal: user@EXAMPLE.COM
+
+Valid starting       Expires              Service principal
+01/07/2015 11:56:35  01/08/2015 11:56:35  krbtgt/EXAMPLE.COM@EXAMPLE.COM
+	renew <span class="k">until </span>01/14/2015 11:56:35
+</code></pre>
+</div>
+
+<h4 id="configuration">Configuration</h4>
+
+<p>The second thing clients need to do is to set up their client configuration file. By
+default, this file is stored in <code class="highlighter-rouge">~/.accumulo/config</code> or <code class="highlighter-rouge">/path/to/accumulo/client.conf</code>.
+Accumulo utilities also allow you to provide your own copy of this file in any location
+using the <code class="highlighter-rouge">--config-file</code> command line option.</p>
+
+<p>Three items need to be set to enable access to Accumulo:</p>
+
+<ul>
+  <li><code class="highlighter-rouge">instance.rpc.sasl.enabled</code>=<em>true</em></li>
+  <li><code class="highlighter-rouge">rpc.sasl.qop</code>=<em>auth</em></li>
+  <li><code class="highlighter-rouge">kerberos.server.primary</code>=<em>accumulo</em></li>
+</ul>
+
+<p>Each of these properties <em>must</em> match the configuration of the accumulo servers; this is
+required to set up the SASL transport.</p>
+
+<h4 id="verifying-administrative-access">Verifying Administrative Access</h4>
+
+<p>At this point you should have enough configured on the server and client side to interact with
+the system. You should verify that the administrative user you chose earlier can successfully
+interact with the sytem.</p>
+
+<p>While this example logs in via <code class="highlighter-rouge">kinit</code> with a password, any login method that caches Kerberos tickets
+should work.</p>
+
+<div class="language-shell highlighter-rouge"><pre class="highlight"><code><span class="gp">$ </span>kinit accumulo_admin@EXAMPLE.COM
+Password <span class="k">for </span>accumulo_admin@EXAMPLE.COM: <span class="k">******************************</span>
+<span class="gp">$ </span>accumulo shell
+
+Shell - Apache Accumulo Interactive Shell
+-
+- version: 1.7.2
+- instance name: MYACCUMULO
+- instance id: 483b9038-889f-4b2d-b72b-dfa2bb5dbd07
+-
+- <span class="nb">type</span> <span class="s1">'help'</span> <span class="k">for </span>a list of available commands
+-
+<span class="gp">accumulo_admin@EXAMPLE.COM@MYACCUMULO&gt; </span>userpermissions
+System permissions: System.GRANT, System.CREATE_TABLE, System.DROP_TABLE, System.ALTER_TABLE, System.CREATE_USER, System.DROP_USER, System.ALTER_USER, System.SYSTEM, System.CREATE_NAMESPACE, System.DROP_NAMESPACE, System.ALTER_NAMESPACE, System.OBTAIN_DELEGATION_TOKEN
+
+Namespace permissions <span class="o">(</span>accumulo<span class="o">)</span>: Namespace.READ, Namespace.ALTER_TABLE
+
+Table permissions <span class="o">(</span>accumulo.metadata<span class="o">)</span>: Table.READ, Table.ALTER_TABLE
+Table permissions <span class="o">(</span>accumulo.replication<span class="o">)</span>: Table.READ
+Table permissions <span class="o">(</span>accumulo.root<span class="o">)</span>: Table.READ, Table.ALTER_TABLE
+
+<span class="gp">accumulo_admin@EXAMPLE.COM@MYACCUMULO&gt; </span>quit
+<span class="gp">$ </span>kdestroy
+<span class="err">$</span>
+</code></pre>
+</div>
+
+<h4 id="delegationtokens-with-mapreduce">DelegationTokens with MapReduce</h4>
+
+<p>To use DelegationTokens in a custom MapReduce job, the call to <code class="highlighter-rouge">setConnectorInfo()</code> method
+on <code class="highlighter-rouge">AccumuloInputFormat</code> or <code class="highlighter-rouge">AccumuloOutputFormat</code> should be the only necessary change. Instead
+of providing an instance of a <code class="highlighter-rouge">KerberosToken</code>, the user must call <code class="highlighter-rouge">SecurityOperations.getDelegationToken</code>
+using a <code class="highlighter-rouge">Connector</code> obtained with that <code class="highlighter-rouge">KerberosToken</code>, and pass the <code class="highlighter-rouge">DelegationToken</code> to
+<code class="highlighter-rouge">setConnectorInfo</code> instead of the <code class="highlighter-rouge">KerberosToken</code>. It is expected that the user launching
+the MapReduce job is already logged in via Kerberos via a keytab or via a locally-cached
+Kerberos ticket-granting-ticket (TGT).</p>
+
+<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="n">Instance</span> <span class="n">instance</span> <span class="o">=</span> <span class="n">getInstance</span><span class="o">();</span>
+<span class="n">KerberosToken</span> <span class="n">kt</span> <span class="o">=</span> <span class="k">new</span> <span class="n">KerberosToken</span><span class="o">();</span>
+<span class="n">Connector</span> <span class="n">conn</span> <span class="o">=</span> <span class="n">instance</span><span class="o">.</span><span class="na">getConnector</span><span class="o">(</span><span class="n">principal</span><span class="o">,</span> <span class="n">kt</span><span class="o">);</span>
+<span class="n">DelegationToken</span> <span class="n">dt</span> <span class="o">=</span> <span class="n">conn</span><span class="o">.</span><span class="na">securityOperations</span><span class="o">().</span><span class="na">getDelegationToken</span><span class="o">();</span>
+
+<span class="c1">// Reading from Accumulo</span>
+<span class="n">AccumuloInputFormat</span><span class="o">.</span><span class="na">setConnectorInfo</span><span class="o">(</span><span class="n">job</span><span class="o">,</span> <span class="n">principal</span><span class="o">,</span> <span class="n">dt</span><span class="o">);</span>
+
+<span class="c1">// Writing to Accumulo</span>
+<span class="n">AccumuloOutputFormat</span><span class="o">.</span><span class="na">setConnectorInfo</span><span class="o">(</span><span class="n">job</span><span class="o">,</span> <span class="n">principal</span><span class="o">,</span> <span class="n">dt</span><span class="o">);</span>
+</code></pre>
+</div>
+
+<p>If the user passes a <code class="highlighter-rouge">KerberosToken</code> to the <code class="highlighter-rouge">setConnectorInfo</code> method, the implementation will
+attempt to obtain a <code class="highlighter-rouge">DelegationToken</code> automatically, but this does have limitations
+based on the other MapReduce configuration methods already called and permissions granted
+to the calling user. It is best for the user to acquire the DelegationToken on their own
+and provide it directly to <code class="highlighter-rouge">setConnectorInfo</code>.</p>
+
+<p>Users must have the <code class="highlighter-rouge">DELEGATION_TOKEN</code> system permission to call the <code class="highlighter-rouge">getDelegationToken</code>
+method. The obtained delegation token is only valid for the requesting user for a period
+of time dependent on Accumulo’s configuration (<code class="highlighter-rouge">general.delegation.token.lifetime</code>).</p>
+
+<p>It is also possible to obtain and use <code class="highlighter-rouge">DelegationToken</code>s outside of the context
+of MapReduce.</p>
+
+<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="n">String</span> <span class="n">principal</span> <span class="o">=</span> <span class="s">"user@REALM"</span><span class="o">;</span>
+<span class="n">Instance</span> <span class="n">instance</span> <span class="o">=</span> <span class="n">getInstance</span><span class="o">();</span>
+<span class="n">Connector</span> <span class="n">connector</span> <span class="o">=</span> <span class="n">instance</span><span class="o">.</span><span class="na">getConnector</span><span class="o">(</span><span class="n">principal</span><span class="o">,</span> <span class="k">new</span> <span class="n">KerberosToken</span><span class="o">());</span>
+<span class="n">DelegationToken</span> <span class="n">delegationToken</span> <span class="o">=</span> <span class="n">connector</span><span class="o">.</span><span class="na">securityOperations</span><span class="o">().</span><span class="na">getDelegationToken</span><span class="o">();</span>
+
+<span class="n">Connector</span> <span class="n">dtConnector</span> <span class="o">=</span> <span class="n">instance</span><span class="o">.</span><span class="na">getConnector</span><span class="o">(</span><span class="n">principal</span><span class="o">,</span> <span class="n">delegationToken</span><span class="o">);</span>
+</code></pre>
+</div>
+
+<p>Use of the <code class="highlighter-rouge">dtConnector</code> will perform each operation as the original user, but without
+their Kerberos credentials.</p>
+
+<p>For the duration of validity of the <code class="highlighter-rouge">DelegationToken</code>, the user <em>must</em> take the necessary precautions
+to protect the <code class="highlighter-rouge">DelegationToken</code> from prying eyes as it can be used by any user on any host to impersonate
+the user who requested the <code class="highlighter-rouge">DelegationToken</code>. YARN ensures that passing the delegation token from the client
+JVM to each YARN task is secure, even in multi-tenant instances.</p>
+
+<h3 id="debugging">Debugging</h3>
+
+<p><strong>Q</strong>: I have valid Kerberos credentials and a correct client configuration file but
+I still get errors like:</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>java.io.IOException: Failed on local exception: java.io.IOException: javax.security.sasl.SaslException: GSS initiate failed [Caused by GSSException: No valid credentials provided (Mechanism level: Failed to find any Kerberos tgt)]
+</code></pre>
+</div>
+
+<p><strong>A</strong>: When you have a valid client configuration and Kerberos TGT, it is possible that the search
+path for your local credentials cache is incorrect. Check the value of the KRB5CCNAME environment
+value, and ensure it matches the value reported by <code class="highlighter-rouge">klist</code>.</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>$ echo $KRB5CCNAME
+
+$ klist
+Ticket cache: FILE:/tmp/krb5cc_123
+Default principal: user@EXAMPLE.COM
+
+Valid starting       Expires              Service principal
+01/07/2015 11:56:35  01/08/2015 11:56:35  krbtgt/EXAMPLE.COM@EXAMPLE.COM
+	renew until 01/14/2015 11:56:35
+$ export KRB5CCNAME=/tmp/krb5cc_123
+$ echo $KRB5CCNAME
+/tmp/krb5cc_123
+</code></pre>
+</div>
+
+<p><strong>Q</strong>: I thought I had everything configured correctly, but my client/server still fails to log in.
+I don’t know what is actually failing.</p>
+
+<p><strong>A</strong>: Add the following system property to the JVM invocation:</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>-Dsun.security.krb5.debug=true
+</code></pre>
+</div>
+
+<p>This will enable lots of extra debugging at the JVM level which is often sufficient to
+diagnose some high-level configuration problem. Client applications can add this system property by
+hand to the command line and Accumulo server processes or applications started using the <code class="highlighter-rouge">accumulo</code>
+script by adding the property to <code class="highlighter-rouge">JAVA_OPTS</code> in <code class="highlighter-rouge">accumulo-env.sh</code>.</p>
+
+<p>Additionally, you can increase the log4j levels on <code class="highlighter-rouge">org.apache.hadoop.security</code>, which includes the
+Hadoop <code class="highlighter-rouge">UserGroupInformation</code> class, which will include some high-level debug statements. This
+can be controlled in your client application, or using <code class="highlighter-rouge">log4j-service.properties</code></p>
+
+<p><strong>Q</strong>: All of my Accumulo processes successfully start and log in with their
+keytab, but they are unable to communicate with each other, showing the
+following errors:</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>2015-01-12 14:47:27,055 [transport.TSaslTransport] ERROR: SASL negotiation failure
+javax.security.sasl.SaslException: GSS initiate failed [Caused by GSSException: No valid credentials provided (Mechanism level: Server not found in Kerberos database (7) - LOOKING_UP_SERVER)]
+        at com.sun.security.sasl.gsskerb.GssKrb5Client.evaluateChallenge(GssKrb5Client.java:212)
+        at org.apache.thrift.transport.TSaslClientTransport.handleSaslStartMessage(TSaslClientTransport.java:94)
+        at org.apache.thrift.transport.TSaslTransport.open(TSaslTransport.java:253)
+        at org.apache.thrift.transport.TSaslClientTransport.open(TSaslClientTransport.java:37)
+        at org.apache.accumulo.core.rpc.UGIAssumingTransport$1.run(UGIAssumingTransport.java:53)
+        at org.apache.accumulo.core.rpc.UGIAssumingTransport$1.run(UGIAssumingTransport.java:49)
+        at java.security.AccessController.doPrivileged(Native Method)
+        at javax.security.auth.Subject.doAs(Subject.java:415)
+        at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1628)
+        at org.apache.accumulo.core.rpc.UGIAssumingTransport.open(UGIAssumingTransport.java:49)
+        at org.apache.accumulo.core.rpc.ThriftUtil.createClientTransport(ThriftUtil.java:357)
+        at org.apache.accumulo.core.rpc.ThriftUtil.createTransport(ThriftUtil.java:255)
+        at org.apache.accumulo.server.master.LiveTServerSet$TServerConnection.getTableMap(LiveTServerSet.java:106)
+        at org.apache.accumulo.master.Master.gatherTableInformation(Master.java:996)
+        at org.apache.accumulo.master.Master.access$600(Master.java:160)
+        at org.apache.accumulo.master.Master$StatusThread.updateStatus(Master.java:911)
+        at org.apache.accumulo.master.Master$StatusThread.run(Master.java:901)
+Caused by: GSSException: No valid credentials provided (Mechanism level: Server not found in Kerberos database (7) - LOOKING_UP_SERVER)
+        at sun.security.jgss.krb5.Krb5Context.initSecContext(Krb5Context.java:710)
+        at sun.security.jgss.GSSContextImpl.initSecContext(GSSContextImpl.java:248)
+        at sun.security.jgss.GSSContextImpl.initSecContext(GSSContextImpl.java:179)
+        at com.sun.security.sasl.gsskerb.GssKrb5Client.evaluateChallenge(GssKrb5Client.java:193)
+        ... 16 more
+Caused by: KrbException: Server not found in Kerberos database (7) - LOOKING_UP_SERVER
+        at sun.security.krb5.KrbTgsRep.&lt;init&gt;(KrbTgsRep.java:73)
+        at sun.security.krb5.KrbTgsReq.getReply(KrbTgsReq.java:192)
+        at sun.security.krb5.KrbTgsReq.sendAndGetCreds(KrbTgsReq.java:203)
+        at sun.security.krb5.internal.CredentialsUtil.serviceCreds(CredentialsUtil.java:309)
+        at sun.security.krb5.internal.CredentialsUtil.acquireServiceCreds(CredentialsUtil.java:115)
+        at sun.security.krb5.Credentials.acquireServiceCreds(Credentials.java:454)
+        at sun.security.jgss.krb5.Krb5Context.initSecContext(Krb5Context.java:641)
+        ... 19 more
+Caused by: KrbException: Identifier doesn't match expected value (906)
+        at sun.security.krb5.internal.KDCRep.init(KDCRep.java:143)
+        at sun.security.krb5.internal.TGSRep.init(TGSRep.java:66)
+        at sun.security.krb5.internal.TGSRep.&lt;init&gt;(TGSRep.java:61)
+        at sun.security.krb5.KrbTgsRep.&lt;init&gt;(KrbTgsRep.java:55)
+        ... 25 more
+</code></pre>
+</div>
+
+<p>or</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>2015-01-12 14:47:29,440 [server.TThreadPoolServer] ERROR: Error occurred during processing of message.
+java.lang.RuntimeException: org.apache.thrift.transport.TTransportException: Peer indicated failure: GSS initiate failed
+        at org.apache.thrift.transport.TSaslServerTransport$Factory.getTransport(TSaslServerTransport.java:219)
+        at org.apache.accumulo.core.rpc.UGIAssumingTransportFactory$1.run(UGIAssumingTransportFactory.java:51)
+        at org.apache.accumulo.core.rpc.UGIAssumingTransportFactory$1.run(UGIAssumingTransportFactory.java:48)
+        at java.security.AccessController.doPrivileged(Native Method)
+        at javax.security.auth.Subject.doAs(Subject.java:356)
+        at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1608)
+        at org.apache.accumulo.core.rpc.UGIAssumingTransportFactory.getTransport(UGIAssumingTransportFactory.java:48)
+        at org.apache.thrift.server.TThreadPoolServer$WorkerProcess.run(TThreadPoolServer.java:208)
+        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
+        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
+        at java.lang.Thread.run(Thread.java:745)
+Caused by: org.apache.thrift.transport.TTransportException: Peer indicated failure: GSS initiate failed
+        at org.apache.thrift.transport.TSaslTransport.receiveSaslMessage(TSaslTransport.java:190)
+        at org.apache.thrift.transport.TSaslServerTransport.handleSaslStartMessage(TSaslServerTransport.java:125)
+        at org.apache.thrift.transport.TSaslTransport.open(TSaslTransport.java:253)
+        at org.apache.thrift.transport.TSaslServerTransport.open(TSaslServerTransport.java:41)
+        at org.apache.thrift.transport.TSaslServerTransport$Factory.getTransport(TSaslServerTransport.java:216)
+        ... 10 more
+</code></pre>
+</div>
+
+<p><strong>A</strong>: As previously mentioned, the hostname, and subsequently the address each Accumulo process is bound/listening
+on, is extremely important when negotiating an SASL connection. This problem commonly arises when the Accumulo
+servers are not configured to listen on the address denoted by their FQDN.</p>
+
+<p>The values in the Accumulo “hosts” files (In <code class="highlighter-rouge">accumulo/conf</code>: <code class="highlighter-rouge">masters</code>, <code class="highlighter-rouge">monitors</code>, <code class="highlighter-rouge">tservers</code>, <code class="highlighter-rouge">tracers</code>,
+and <code class="highlighter-rouge">gc</code>) should match the instance componentof the Kerberos server principal (e.g. <code class="highlighter-rouge">host</code> in <code class="highlighter-rouge">accumulo/host@EXAMPLE.COM</code>).</p>
+
+<p><strong>Q</strong>: After configuring my system for Kerberos, server processes come up normally and I can interact with the system. However,
+when I attempt to use the “Recent Traces” page on the Monitor UI I get a stacktrace similar to:</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>java.lang.AssertionError: AuthenticationToken should not be null
+    at org.apache.accumulo.monitor.servlets.trace.Basic.getScanner(Basic.java:139)
+    at org.apache.accumulo.monitor.servlets.trace.Summary.pageBody(Summary.java:164)
+    at org.apache.accumulo.monitor.servlets.BasicServlet.doGet(BasicServlet.java:63)
+    at javax.servlet.http.HttpServlet.service(HttpServlet.java:687)
+    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
+    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:738)
+    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:551)
+    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
+    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:568)
+    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:221)
+    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1111)
+    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:478)
+    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:183)
+    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1045)
+    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
+    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:97)
+    at org.eclipse.jetty.server.Server.handle(Server.java:462)
+    at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:279)
+    at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:232)
+    at org.eclipse.jetty.io.AbstractConnection$2.run(AbstractConnection.java:534)
+    at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:607)
+    at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:536)
+    at java.lang.Thread.run(Thread.java:745)
+</code></pre>
+</div>
+
+<p><strong>A</strong>: This indicates that the Monitor has not been able to successfully log in a client-side user to read from the <code class="highlighter-rouge">trace</code> table. Accumulo allows the TraceServer to rely on the property <code class="highlighter-rouge">general.kerberos.keytab</code> as a fallback when logging in the trace user if the <code class="highlighter-rouge">trace.token.property.keytab</code> property isn’t defined. Some earlier versions of Accumulo did not do this same fallback for the Monitor’s use of the trace user. The end result is that if you configure <code class="highlighter-rouge">general.kerberos.keytab</code> and not <code class="highlighter-rouge">trace.token.property.keytab</code> you will end up with a system that properly logs trace information but can’t view it.</p>
+
+<p>Ensure you have set <code class="highlighter-rouge">trace.token.property.keytab</code> to point to a keytab for the principal defined in <code class="highlighter-rouge">trace.user</code> in the <code class="highlighter-rouge">accumulo-site.xml</code> file for the Monitor, since that should work in all versions of Accumulo.</p>
+
+  </div>
+</div>
+
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+
+  <p>Copyright © 2011-2017 The Apache Software Foundation. Licensed under the <a href="https://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
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