---> "Can it happen that we end up with 2 leaders or 0 leader for some period of time (for example, during network delays/partitions)?" look at the code: https://github.com/apache/curator/blob/master/curator-recipes/src/main/java/org/apache/curator/framework/recipes/leader/LeaderSelector.java#L340 it can guarantee exactly one leader all the time(EPHEMERAL_SEQUENTIAL zk-node) which has not too much correlations with the network partitions of zk ensembles itself. I guess,haha! ----- 原始邮件 ----- 发件人：Michael Borokhovich <michael...@gmail.com> 收件人：dev@zookeeper.apache.org, maoling199210...@sina.com 主题：Re: Leader election 日期：2018年12月06日 15点18分
Thanks, I will check it out. However, do you know if it gives any better guarantees? Can it happen that we end up with 2 leaders or 0 leader for some period of time (for example, during network delays/partitions)? On Wed, Dec 5, 2018 at 10:54 PM 毛蛤丝 <maoling199210...@sina.com> wrote: > suggest you use the ready-made implements of curator: > http://curator.apache.org/curator-recipes/leader-election.html > ----- 原始邮件 ----- > 发件人：Michael Borokhovich <michael...@gmail.com> > 收件人："dev@zookeeper.apache.org" <dev@zookeeper.apache.org> > 主题：Leader election > 日期：2018年12月06日 07点29分 > > Hello, > We have a service that runs on 3 hosts for high availability. However, at > any given time, exactly one instance must be active. So, we are thinking to > use Leader election using Zookeeper. > To this goal, on each service host we also start a ZK server, so we have a > 3-nodes ZK cluster and each service instance is a client to its dedicated > ZK server. > Then, we implement a leader election on top of Zookeeper using a basic > recipe: > https://zookeeper.apache.org/doc/r3.1.2/recipes.html#sc_leaderElection. > I have the following questions doubts regarding the approach: > 1. It seems like we can run into inconsistency issues when network > partition occurs. Zookeeper documentation says that the inconsistency > period may last “tens of seconds”. Am I understanding correctly that during > this time we may have 0 or 2 leaders? > 2. Is it possible to reduce this inconsistency time (let's say to 3 > seconds) by tweaking tickTime and syncLimit parameters? > 3. Is there a way to guarantee exactly one leader all the time? Should we > implement a more complex leader election algorithm than the one suggested > in the recipe (using ephemeral_sequential nodes)? > Thanks, > Michael. >
