Sorry for the confusion in terminology, I was unfamiliar with the exact leader/follower semantics previously.
So if all connected servers update their config file, does that mean that non-voting followers who aren't part of the new ensemble will lose the entry specific to them in their config file? I can test this myself, but getting an inside perspective is very helpful. Thanks again for the help! Jared On Jul 27, 2012, at 6:55 PM, Alexander Shraer <[email protected]> wrote: > Yes, any number of followers which are not in the configuration can just > connect and listen in. This has always been the case, also in 3.4, I just > made use of this for the purpose of adding members during reconfiguration. > Moreover, in 3.4 there this bug ZOOKEEPER-1113 > where the leader actually counts the votes of anyone connected, regardless of > config membership :) This is fixed in ZK-107, so they are really non-voting > followers. > > > I am assuming that's the case, and that it is a follower (and not > > participant) by virtue of not being in the official configuration stored in > > zookeeper itself. > > Follower and participant types of servers is not something that was defined > in ZK-107. In ZooKeeper every follower/leader is a "participant". Its just > that the votes of participants that are not in the configuration are not > counted that's why we call them non-voting followers. BTW, obviously a > non-voting follower can not become leader (like ZK-1113 this was also not > enforced before ZK-107). > > > And a followup... does zookeeper only overwrite the dynamic > > configuration file for nodes that are voting participants? Such that if I > > started a follower and then left it running through some > > reconfigurations, its file would not get updated if it was never added as > > part of those reconfigurations? > > No, as soon as it connects to the current leader, its dynamic config file is > overwritten with the current configuration as part of the synchronization > with the leader. Every time a new configuration is committed, all connected > servers (voting, non-voting, observers) will update their dynamic config > file, doesn't matter if they're in the config. > > Alex > > On Fri, Jul 27, 2012 at 5:35 PM, Jared Cantwell <[email protected]> > wrote: > So does just having the server started and pointing to the existing ensemble > automatically make it a "non participating follower"? In other words, there > is no need to inform the existing nodes that this new node is joining as a > follower? And to extend that, there could be any number of followers that > are simply listening in on the event stream? I am assuming that's the case, > and that it is a follower (and not participant) by virtue of not being in the > official configuration stored in zookeeper itself. > > On Fri, Jul 27, 2012 at 6:29 PM, Alexander Shraer <[email protected]> wrote: > there are just two supported types - participant and observer. > (participant can act as either follower or leader). > > So you can either write participant or leave it unspecified (which means > participant by default). Also, since the ip is the same for all your ports > you don't have to write it twice. All of these should work in the same way: > > server.5=10.10.5.17:2182:2183:participant;10.10.5.17:2181 > server.5=10.10.5.17:2182:2183:participant;2181 > server.5=10.10.5.17:2182:2183;10.10.5.17:2181 > server.5=10.10.5.17:2182:2183;2181 > > > > On Fri, Jul 27, 2012 at 5:25 PM, Jared Cantwell <[email protected]> > wrote: > Thanks Alex for the response. Our current lines in the configuration look > like this: > > server.5=10.10.5.17:2182:2183:participant;10.10.5.17:2181 > > For the new servers is it ok for their entry to have "participant"? Or > should that be something different (e.g. "follower")? > > ~Jared > > On Fri, Jul 27, 2012 at 6:20 PM, Alexander Shraer <[email protected]> wrote: > Hi Jared, > > Thanks for experimenting with this feature. > > The idea is that new servers join as "non voting followers". Which means that > they act as normal followers but the leader ignores their votes since they > are not part of the current configuration. The leader only counts their votes > during the reconfiguration itself (to make sure a quorum of the new config is > ready before the new config can be committed/activated). Defining them as > observers is not a good idea, for example in your scenario if they were > observers they wouldn't be able to participate in the reconfiguration > protocol (which is similar to the protocol for committing any other operation > in which observers don't participate) and since we don't have a quorum of > followers in the new config that can ack, reconfiguration would throw an > exception (of KeeperException.NEWCONFIGNOQUORUM type). > Of course if you intend them to be observers in the new config you can define > them as observers since their votes are not needed during reconfig anyway. > > You're right, the new servers must be able to connect to the old quorum. At > minimum, their file should contain the current leader, but > you can also copy the current configuration file to the new members if you > wish. > > In addition, you should add a line for the member itself, so that server F > appears in F's config file (Its not important that the other new servers > appear in F's file, but it won't hurt either, so you can do a union of old > and new if you wish). The constructor of QuorumPeer checks that the server > itself is in the configuration its started with, otherwise its not going to > run. This check has always been there, but I'm thinking of possibly changing > it in the future. > > As soon as F connects to the leader, its config file will be overwritten with > the current config file as part of the synchronization process. > > Alex > > > On Fri, Jul 27, 2012 at 10:06 AM, Jared Cantwell <[email protected]> > wrote: > Hi, > > We are testing integration with 3.5.0 and dynamic membership and I have a > question. If I have a current set of servers in my ensemble {A,B,C,D,E} > and I want to reconfigure the ensemble to {D,E,F,G,H}, how should the > dynamic config file on servers F,G,H be configured on startup? Should they > have the old ensemble, the new ensemble, or the union of both ensembles? > It seems like these new servers need to know about the old quorum, but > since they aren't part of it yet its not clear to me how they should be > configured. Should there be an intermediate configuration with F,G, and H > as simply Observers? > > I can't find much documentation on this so I want to make sure I understand > things correctly. > > Thanks! > ~Jared > > > > >
