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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