Tsz Wo Nicholas Sze created HDFS-6371:
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Summary: In HA setup, the standby NN should redirect WebHDFS write
requests to the active NN
Key: HDFS-6371
URL: https://issues.apache.org/jira/browse/HDFS-6371
Project: Hadoop HDFS
Issue Type: Bug
Components: webhdfs
Reporter: Tsz Wo Nicholas Sze
Assignee: Tsz Wo Nicholas Sze
The current WebHDFS implementation in namenode does not check its HA state --
it does the same thing no matter it is active or standby.
Suppose a http client talk to the standby NN via WebHDFS. For the read
operations, there is no problem. For the write operations, if the operation
requires http redirect (e.g. creating a file), it will work since the standby
NN will also redirect the client to a DN. When the client connect to the DN,
the DN will fulfill the request with the active NN. However, for the write
operations not requiring http redirect (e.g. mkdir), the operation will fail
with StandbyException since it will be executed with the standby NN.
There are two solutions:
# The http client could catch StandbyException and then retries with the other
NN in this case.
# The standby NN redirects the request to the active NN.
The second solution seems better since the client does not need to know both
active NN and standby NN.
Note that WebHdfsFileSystem is already able to handle HA failover. The JIRA is
for other http clients.
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