[Bugs] [Bug 1554018] New: 4.0 clients may fail to convert iatt in dict when recieving the same from older (< 4.0) servers

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1554018

            Bug ID: 1554018
           Summary: 4.0 clients may fail to convert iatt in dict when
                    recieving the same from older (< 4.0) servers
           Product: GlusterFS
           Version: 4.0
         Component: protocol
          Keywords: Triaged
          Assignee: srangana at redhat.com
          Reporter: srangana at redhat.com
                CC: atumball at redhat.com, bugs at gluster.org,
                    rgowdapp at redhat.com



Description of problem:

Based on review comments in https://review.gluster.org/#/c/19690 as follows,

Du: Do we support the case of older bricks/servers and newer clients? If yes,
we would face a similar problem. The only difference would be clients expecting
a newer iatt when an old iatt is sent.

Shyam: The problem is similar to the disadvantage/improvement that I had
mentioned in the review comments. If a client has the newer iatt implementation
and connects to an older server, the mapping will fail again. The reasons this
is not a major concern yet is as follows.

Our upgrade procedure and guide states servers first and then clients. So the
environment will get servers upgraded first and then the clients.

Now, a server would be upgraded in a rolling fashion, so say 1 server is
upgraded, then its service clients (quotad, selfheald, others...) would be the
latest, but connect with the older protocol version to the older servers.

Till DHT is not in the stack (as this problem is localized to the iatt in the
dict that DHT requests), we are fine, if any of these service daemons use DHT
in their graph, it may start facing the same/similar problem (rebalance comes
to mind, but we may need to add that to the upgrade guide).

The fix going forward (possibly we need this in 4.1) is to apply a similar fix
to the client stack as well.

Resolution:

The client protocol xlator also needs a translation of iatt in dict to actual
runtime definition of iatt, based on the protocol dialect in question. This
change should be similar to the change in the review mentioned above.

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