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From PramodSSImmaneni <...@git.apache.org>
Subject [GitHub] incubator-apex-core pull request: APEXCORE-455 Added documentation...
Date Thu, 12 May 2016 22:40:48 GMT
Github user PramodSSImmaneni commented on a diff in the pull request:

    --- Diff: docs/security.md ---
    @@ -76,6 +51,72 @@ The property `dt.authentication.principal` specifies the Kerberos user
     The subsequent sections talk about how security works in Apex. This information is not
needed by users but is intended for the inquisitive techical audience who want to know how
security works.
    +### Token Refresh
    +Apex applications, at runtime, use delegation tokens to authenticate with Hadoop services
when communicating with them as described in the security architecture section below. The
delegation tokens are originally issued by these Hadoop services and have an expiry time period
which is typically 7 days. The tokens become invalid beyond this time and the applications
will no longer be able to communicate with the Hadoop services. For long running applications
this presents a problem.
    +To solve this problem one of the two approaches can be taken. The first approach is to
change the Hadoop configuration itself to extend the token expiry time period. This may not
be possible in all environments as it requires a change in the security policy as the tokens
will now be valid for a longer period of time and the change also requires administrator privileges
to Hadoop. The second approach is to use a feature available in apex to auto-refresh the tokens
before they expire. Both the approaches are detailed below and the users can choose the one
that works best for them.
    +####Hadoop configuration approach
    +An Apex application uses delegation tokens to authenticate with Hadoop services, Resource
Manager (YARN) and Name Node (HDFS), and these tokens are issued by those services respectively.
Since the application is long-running, the tokens can expire while the application is still
running. Hadoop uses configuration settings to set the maximum lifetime of the tokens. In
this approach these setings are increased to cover the lifetime of the application. There
are separate settings for ResourceManager and NameNode delegation tokens.
    +The ResourceManager delegation token max lifetime is specified in `yarn-site.xml` and
can be specified as follows for example for a lifetime of 1 year
    --- End diff --
    Got it I will let you know once I update it.

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