[jira] [Created] (HDFS-15588) Arbitrarily low values for `dfs.block.access.token.lifetime` aren't safe and can cause a healthy datanode to be excluded

["sr2020 (Jira)" <ji...@apache.org>]

sr2020 created HDFS-15588:
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             Summary: Arbitrarily low values for `dfs.block.access.token.lifetime` aren't safe and can cause a healthy datanode to be excluded
                 Key: HDFS-15588
                 URL: https://issues.apache.org/jira/browse/HDFS-15588
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: hdfs, hdfs-client, security
            Reporter: sr2020


*Description*:
Setting `dfs.block.access.token.lifetime` to arbitrarily low values (like 1) means the lifetime of a block token is very short, as a result some healthy datanodes could be wrongly excluded by the client due to the `InvalidBlockTokenException`.

More specifically, in `nextBlockOutputStream`, the client tries to get the `accessToken` from the namenode and use it to talk to datanode. And the lifetime of `accessToken` could set to very small (like 1 min) by setting `dfs.block.access.token.lifetime`. In some extreme conditions (like a VM migration, temporary network issue, or a stop-the-world GC), the `accessToken` could become expired when the client tries to use it to talk to the datanode. If expired, `createBlockOutputStream` will return false (and mask the `InvalidBlockTokenException`), so the client will think the datanode is unhealthy, mark the it as "excluded" and will never read/write on it.


*Proposed solution*:
A simple retry on the same datanode after catching `InvalidBlockTokenException` can solve this problem (assuming the extreme conditions won't happen often). Since currently the `dfs.block.access.token.lifetime` can even accept values like 0, we can also choose to prevent the users from setting `dfs.block.access.token.lifetime` to a small value (e.g., we can enforce a minimum value of 5mins for this parameter).

We submit a patch for retrying after catching `InvalidBlockTokenException` in `nextBlockOutputStream`. We can also provide a patch for enforcing a larger minimum value for `dfs.block.access.token.lifetime` if it is a better way to handle this.




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