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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-2420) [DAC] HDFS and ZK access delegation
Date Wed, 07 Apr 2010 19:52:33 GMT
[DAC] HDFS and ZK access delegation
-----------------------------------

                 Key: HBASE-2420
                 URL: https://issues.apache.org/jira/browse/HBASE-2420
             Project: Hadoop HBase
          Issue Type: Sub-task
            Reporter: Andrew Purtell


HBase security will be in part layered on top of HDFS security, and whatever ZK offers as
well. For sake of discussion we presume both HDFS and ZK use a Kerberos based authentication
and authorization model, as proposed in the Hadoop Security Architecture document. There are
two basic options for that, fine- or coarse-grained:

h4. Coarse
There could simply be a single delegation token granted to a HBase cluster from HDFS and ZK
for all operations on behalf of all possible users of the HBase cluster. From the perspective
of HDFS and ZK, there is only a single principal for each cluster.

h4. Fine
The HBase master could manage and renew HDFS and ZK delegation tokens on behalf of users authenticated
to HBase via Kerberos. So when a client authenticates via KRB to the HMaster when looking
up region locations as the first step to any HBase access, the HMaster would get a delegation
token from the NameNode on behalf of the user. (The user would then hand the delegation token
to the HRegionServers to allow access to store data via their embedded DFSClients.) It would
be ideal if ZooKeeper authentication and authorization could tie in seamlessly. For example,
at the same time the HMaster is getting a delegation token for the user for HDFS, it could
also get another token for ZK on behalf of the user. A wrinkle here is token renewal. If a
user transacts with a HRegionServer with an expired token, the HRegionServer would renew the
token (or ask the HMaster to renew the token if superuser should not be delegated from HMaster
to HRegionServer) transparently with the NameNode on behalf of the user. Something like that
would be necessary on the ZK side also. To support this model, the HRegionServers and HMaster
(or just HMaster) must act as a superuser principal capable of impersonating user principals.
Presumably, with the ZK ensemble also. Thus ZK, like HDFS, must provide methods for a superuser
to act on behalf of others. HDFS will have this facility. 

There are pros and cons for each approach. Coarse obviously is much more simple to implement
and reason about. But it requires more trust in HBase to maintain isolation between users
than the fine-grained approach. With the fine-grained approach, the regionservers get HDFS
and ZK delegation tokens from the HBase client and this allows a policy where files and znodes
created by one user+group cannot be read or written by another at the DFS (store) level or
the ZK level. Assume group level permissions. Thus you can reason about isolation further
down the stack, not just from client->HBase, but client->HBase->HDFS and client->ZK
and client->HBase->ZK. 

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