Mohammad Kamrul Islam created HDFS-12621:
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Summary: Inconsistency/confusion around
ViewFileSystem.getDelagation
Key: HDFS-12621
URL: https://issues.apache.org/jira/browse/HDFS-12621
Project: Hadoop HDFS
Issue Type: Bug
Affects Versions: 2.7.3
Reporter: Mohammad Kamrul Islam
*Symptom*:
When a user invokes ViewFileSystem.getDelegationToken(String renewer), she gets
a "null". However, for any other file system, it returns a valid delegation
token. For a normal user, it is very confusing and it takes substantial time to
debug/find out an alternative.
*Root Cause:*
ViewFileSystem inherits the basic implementation from
FileSystem.getDelegationToken() that returns "_null_". The comments in the
source code indicates not to use it and instead use addDelegationTokens().
However, it works fine DistributedFileSystem.
In short, the same client call is working for hdfs:// but not for viewfs://.
And there is no way of end-user to identify the root cause. This also creates a
lot of confusion for any service that are supposed to work for both viewfs and
hdfs.
*Possible Solution*:
_Option 1:_ Add a LOG.warn() with reasons/alternative before returning "null"
in the base class.
_Option 2:_ As done for other FS, ViewFileSystem can override the method with a
implementation by returning the token related to fs.defaultFS. In this case,
the defaultFS is something like "viewfs://..". We need to find out the actual
namenode and uses that to retrieve the delegation token.
_Option 3:_ Open for suggestion ?
*Last note:* My hunch is : there are very few users who may be using viewfs://
with Kerberos. Therefore, it was not being exposed earlier.
I'm working on a good solution. Please add your suggestion.
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