Il giorno mar 11 feb 2020 alle ore 09:12 Szalay-Bekő Máté <szalay.beko.m...@gmail.com> ha scritto: > > Hi All, > > about the question from Michael: > > 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? > > In this particular case, it might be enough. The protocol change happened > now in the 'initial message' sent by the QuorumCnxManager. Maybe it is not > a problem if the new servers can not initiate channels to the old servers, > maybe it is enough if these channel gets initiated by the old servers only. > I will test it quickly. > > Although I have no idea if any other thing changed in the quorum protocol > between 3.5 and 3.6. In other cases it might not be enough if the new > servers can understand the old messages, as the old servers can break by > not understanding the messages from the new servers. Also, in the code > currently (AFAIK) there is no generic knowledge of protocol versions, the > servers are not storing that which protocol versions they can/should use to > communicate to which particular other servers. Maybe we don't even need > this, but I would feel better if we would have more tests around these > things. > > My suggestion for the long term: > - let's fix this particular issue now with 3.6.0 quickly (I start doing > this today) > - let's do some automation (backed up with jenkins) that will test a whole > combinations of different ZooKeeper upgrade paths by making rolling > upgrades during some light traffic. Let's have a bit better definition > about what we expect (e.g. the quorum is up, but some clients can get > disconnected? What will happen to the ephemeral nodes? Do we want to > gracefully close or transfer the user sessions before stopping the old > server?) and let's see where this broke. Just by checking the code, I don't > think the quorum will always be up (e.g. between older 3.4 versions and > 3.5).
I am happy to work on this topic > - we need to update the Wiki about the working rolling upgrade paths and > maybe about workarounds if needed > - we might need to do some fixes (adding backward compatible versions > and/or specific parameters that enforce old protocol temporary during the > rolling upgrade that can be changed later to the new protocol by either > dynamic reconfig or by rolling restart) it would be much better on 3.6 code to have some support for compatibility with 3.5 servers we can't require old code to be forward compatible but we can make new code be compatible to a certain extend with old code. If we can achieve this compatibility goal without a flag is better, users won't have to care about this part and they simply "trust" on us The rollback story is also important, but maybe we are still not ready for it, in case of local changes to store, it is better to have a clear design and plan and work for a new release (3.7?) Enrico > > Depending on your comments, I am happy to create a few Jira tickets around > these topics. > > Kind regards, > Mate > > ps. Enrico, sorry about your RC... I owe you a beer, let me know if you are > near to Budapest ;) > > On Tue, Feb 11, 2020 at 8:43 AM Enrico Olivelli <eolive...@gmail.com> wrote: > > > Good. > > > > I will cancel the vote for 3.6.0rc2. > > > > I appreciate very much If Mate and his colleagues have time to work on a > > fix. > > Otherwise I will have cycles next week > > > > I would also like to spend my time in setting up a few minimal integration > > tests about the upgrade story > > > > Enrico > > > > Il Mar 11 Feb 2020, 07:30 Michael Han <h...@apache.org> ha scritto: > > > > > 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 > > > > > > >>> > > > > > > > > > > > > > > > > > > > > >
