Hi, even if we had enough binding +1 on 3.6.0rc2 before closing the VOTE of 3.6.0 I wanted to finish my tests and I am coming to an apparent blocker.
I am trying to upgrade a 3.5.6 cluster to 3.6.0, but it looks like peers are not able to talk to each other. I have a cluster of 3, server1, server2 and server3. When I upgrade server1 to 3.6.0rc2 I see this kind of errors on 3.5 nodes: 2020-02-10 09:35:07,745 [myid:3] - INFO [localhost/127.0.0.1:3334:QuorumCnxManager$Listener@918] - Received connection request 127.0.0.1:62591 2020-02-10 09:35:07,746 [myid:3] - ERROR [localhost/127.0.0.1:3334:QuorumCnxManager@527] - org.apache.zookeeper.server.quorum.QuorumCnxManager$InitialMessage$InitialMessageException: Got unrecognized protocol version -65535 Once I upgrade all of the peers the system is up and running, without apparently no data loss. During the upgrade as soon as I upgrade the first node, say, server1, server1 is not able to accept connections (error "Close of session 0x0 java.io.IOException: ZooKeeperServer not running") from clients, this is expected, because as far as it cannot talk with the other peers it is practically partitioned away from the cluster. My questions are: 1) is this expected ? I can't remember protocol changes from 3.5 to 3.6, but actually 3.6 diverged from 3.5 branch so long ago, and I was not in the community as dev so I cannot tell 2) is this a viable option for users ? to have some temporary glitch during the upgrade and hope that the upgrade completes without troubles ? In theory as long as two servers are running the same major version (3.5 or 3.6) we have a quorum and the system is able to make progress and to server clients. I feel that this is quite dangerous, but I don't have enough context to understand how this problem is possible and when we decided to break compatibility. The other option is that I am wrong in my test and I am messing up :-) The other upgrade path I would like to see working like a charm is the upgrade from 3.4 to 3.6, as I see that as soon as we release 3.6 we should encourage users to move to 3.6 and not to 3.5. Regards Enrico
