Kudos Enrico, very thorough work as the final gate keeper of the release! Now with this, I'd like to *vote a -1* on the 3.6.0 RC2.
I'd recommend we fix this issue for 3.6.0. ZooKeeper is one of the rare piece of software that put so much emphasis on compatibilities thus it just works when upgrade / downgrade, which is amazing. One guarantee we always had is during rolling upgrade, the quorum will always be available, leading to no service interruption. It would be sad we lose such capability given this is still a tractable problem. Regarding the fix, can we just make 3.6.0 aware of the old protocol and speak old message format when it's talking to old server? Basically, an ugly if else check against the protocol version should work and there is no need to have multiple pass on rolling upgrade process. On Mon, Feb 10, 2020 at 10:23 PM Enrico Olivelli <eolive...@gmail.com> wrote: > I suggest this plan: > - release 3.6.0 now > - improve the migration story, the flow outlined by Mate is > interesting, but it will take time > > 3.6.0rc2 got enough binding votes so I am going to finalize the > release this evening (within 8-10 hours) if no one comes out in the > VOTE thread with a -1 > > Enrico > > Enrico > > Il giorno lun 10 feb 2020 alle ore 19:33 Patrick Hunt > <ph...@apache.org> ha scritto: > > > > On Mon, Feb 10, 2020 at 3:38 AM Andor Molnar <an...@apache.org> wrote: > > > > > Hi, > > > > > > Answers inline. > > > > > > > > > > In my experience when you are close to a release it is better to to > > > > make big changes. (I am among the approvers of that patch, so I am > > > > responsible for this change) > > > > > > > > > > > > Although this statement is acceptable for me, I don’t feel this patch > > > should not have been merged into 3.6.0. Submission has been preceded > by a > > > long argument with MAPR folks who originally wanted to be merged into > 3.4 > > > branch (considering the pace how ZooKeeper community is moving > forward) and > > > we reached an agreement that release it with 3.6.0. > > > > > > Make a long story short, this patch has been outstanding for ages > without > > > much attention from the community and contributors made a lot of > effort to > > > get it done before the release. > > > > > > > > > > I would like to ear from people that have been in the community for > > > > long time, then I am ready to complete the release process for > > > > 3.6.0rc2. > > > > > > > > > Me too. > > > > > > I tend to accept the way rolling restart works now - as you described > > > Enrico - and given that situation was pretty much the same between 3.4 > and > > > 3.5, I don’t feel we have to make additional changes. > > > > > > On the other hand, the fix that Mate suggested sounds quite cool, I’m > also > > > happy to work on getting it in. > > > > > > Fyi, Release Management page says the following: > > > > https://cwiki.apache.org/confluence/display/ZOOKEEPER/ReleaseManagement > > > > > > "major.minor release of ZooKeeper must be backwards compatible with the > > > previous minor release, major.(minor-1)" > > > > > > > > Our users, direct and indirect, value the ability to migrate to newer > > versions - esp as we drop support for older. Frictions such as this can > be > > a reason to go elsewhere. I'm "pro" b/w compact - esp given our published > > guidelines. > > > > Patrick > > > > > > > Andor > > > > > > > > > > > > > > > > On 2020. Feb 10., at 11:32, Enrico Olivelli <eolive...@gmail.com> > wrote: > > > > > > > > Thank you Mate for checking and explaining this story. > > > > > > > > I find it very interesting that the cause is ZOOKEEPER-3188 as: > > > > - it is the last "big patch" committed to 3.6 before starting the > > > > release process > > > > - it is the cause of the failure of the first RC > > > > > > > > In my experience when you are close to a release it is better to to > > > > make big changes. (I am among the approvers of that patch, so I am > > > > responsible for this change) > > > > > > > > This is a pointer to the change to whom who wants to understand > better > > > > the context > > > > > > > > https://github.com/apache/zookeeper/pull/1048/files#diff-7a209d890686bcba351d758b64b22a7dR11 > > > > > > > > IIUC even for the upgrade from 3.4 to 3.5 the story was the same and > > > > if this statement holds then I feel we can continue > > > > with this release. > > > > > > > > - Reverting ZOOKEEPER-3188 is not an option for me, it is too > complex. > > > > - Making 3.5 and 3.6 "compatible" can be very tricky and we do not > > > > have tools to certify this compatibility (at least not in the short > > > > term) > > > > > > > > I would like to ear from people that have been in the community for > > > > long time, then I am ready to complete the release process for > > > > 3.6.0rc2. > > > > > > > > I will update the website and the release notes with a specific > > > > warning about the upgrade, we should also update the Wiki > > > > > > > > Enrico > > > > > > > > > > > > Il giorno lun 10 feb 2020 alle ore 11:17 Szalay-Bekő Máté > > > > <szalay.beko.m...@gmail.com> ha scritto: > > > >> > > > >> Hi Enrico! > > > >> > > > >> This is caused by the different PROTOCOL_VERSION in the > > > QuorumCnxManager. > > > >> The Protocol version was changed last time in ZOOKEEPER-2186 > released > > > >> first in 3.4.7 and 3.5.1 to avoid some crashing / fix some bugs. > Later I > > > >> also changed the protocol version when the format of the initial > message > > > >> changed in ZOOKEEPER-3188. So actually the quorum protocol is not > > > >> compatible in this case and is the 'expected' behavior if you > upgrade > > > e.g > > > >> from 3.4.6 to 3.4.7, or 3.4.6 to 3.5.5 or e.g from 3.5.6 to 3.6.0. > > > >> > > > >> We had some discussion in the PR of ZOOKEEPER-3188 back then and > got to > > > the > > > >> conclusion that it is not that bad, as there will be no data loss > as you > > > >> wrote. The tricky thing is that during rolling upgrade we should > ensure > > > >> both backward and forward compatibility to make sure that the old > and > > > the > > > >> new part of the quorum can still speak to each other. The current > > > solution > > > >> (simply failing if the protocol versions mismatch) is more simple > and > > > still > > > >> working just fine: as the servers are restarted one-by-one, the > nodes > > > with > > > >> the old protocol version and the nodes with the new protocol version > > > will > > > >> form two partitions, but any given time only one partition will > have the > > > >> quorum. > > > >> > > > >> Still, thinking it trough, as a side effect in these cases there > will > > > be a > > > >> short time when none of the partitions will have quorums (when we > have N > > > >> servers with the old protocol version, N servers with the new > protocol > > > >> version, and there is one server just being restarted). I am not > sure > > > if we > > > >> can accept this. > > > >> > > > >> For ZOOKEEPER-3188 we can add a small patch to make it possible to > parse > > > >> the initial message of the old protocol version with the new code. > But > > > I am > > > >> not sure if it would be enough (as the old code will not be able to > > > parse > > > >> the new initial message). > > > >> > > > >> One option can be to make a patch also for 3.5 to have a version > which > > > >> supports both protocol versions. (let's say in 3.5.8) Then we can > write > > > to > > > >> the release note, that if you need rolling upgrade from any versions > > > since > > > >> 3.4.7, then you have to first upgrade from 3.5.8 before upgrading to > > > 3.6.0. > > > >> We can even make the same thing on the 3.4 branch. > > > >> > > > >> But I am also new to the community... It would be great to hear the > > > opinion > > > >> of more experienced people. > > > >> Whatever the decision will be, I am happy to make the changes. > > > >> > > > >> And sorry for breaking the RC (if we decide that this needs to be > > > >> changed...). ZOOKEEPER-3188 was a complex patch. > > > >> > > > >> Kind regards, > > > >> Mate > > > >> > > > >> On Mon, Feb 10, 2020 at 9:47 AM Enrico Olivelli < > eolive...@gmail.com> > > > wrote: > > > >> > > > >>> 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 > > > >>> > > > > > > >
