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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2420) [DAC] HDFS and ZK access delegation
Date Wed, 07 Apr 2010 20:56:33 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2420?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12854706#action_12854706
] 

Andrew Purtell commented on HBASE-2420:
---------------------------------------

It's about trust for enforcement of isolation. HBase can run as a single principal across
the whole cluster from the HDFS perspective no matter the details of HBase internal security
model. So as you put it the "hbase" user would own the hfiles. 

bq. Otherwise we'd have to do fine grained ACLs on all HFiles, and granting a user access
to a table would require granting them access to the files involved in that table only.

That's one option. 

Another is a scheme where HBase users are mapped to HBase roles which are mapped to HDFS users
which are aggregated as HDFS groups:

HBase user -> HBase role -> HDFS user -> HDFS group

This can provide some flexibility for various configurations from simple-but-no-isolation
to complex-but-paranoid. This scheme would have the DFSClients in the region servers operate
with multiple delegation tokens from HDFS in a pass through manner. 

The trade off is some complexity for being able to get some assurance of isolation even if
HBase is "broken" in some way. 

> [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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