Re: Zookeeper Leadership election with curator

[Jordan Zimmerman]

A few things:

* You don’t need to create a new Curator instance for each Leader. One Curator 
instance can be used for an application.
* Calling client.getZookeeperClient().blockUntilConnectedOrTimedOut(); is 
unnecessary
* Calling isLeader() immediately after starting the latch may not work. It 
takes time for the leader to get selected. LeaderLatch has a listener if you 
want to get notified. Alternatively, you can use LeaderSelector.

Hope this helps.

-Jordan



On January 15, 2015 at 5:25:26 PM, Check Peck (comptechge...@gmail.com) wrote:

I am using Zookeeper for the leadership election process. I have three nodes 
zookeeper ensemble.

We have a node like this "/test/msn" on which we are doing the leadership 
election and it works fine and we have application servers running it in 
production and using "/test/msn" node for leadership. And this program is 
always running.

Now we created another node like this "/testpnl" in the same zookeeper servers. 
And we have another set of machines which is trying to do the leadership 
election on that node and whenever I run my program in production from one 
servers, it always returns back that the node is not leader? And I can see only 
one node inside "/testpnl" and it is the same node from which I am running my 
program?

I am using Curator 2.7.0 and the zookeeper version is 3.4.5 Is there anything 
wrong with my setup or zookeeper has some bug which I am not aware?

Is anything

    public class ZookeeperLeaderTester {

        private ZookeeperClient zookClient;

        private static final String ZOOK_PRODUCTION = 
"host1:2181,host2:2181,host3:2181";
        private static final String LEADERSHIP_NODE = "/testpnl";

        private static class Holder {
            static final ZookeeperLeaderTester INSTANCE = new 
ZookeeperLeaderTester();
        }

        public static ZookeeperLeaderTester getInstance() {
            return Holder.INSTANCE;
        }

        private ZookeeperLeaderTester() {
            try {
                String hostname = getHostName();

                zookClient = new ZookeeperClient(nodes, LEADERSHIP_NODE, 
hostname);
                zookClient.start();

            } catch (Exception ex) {
                System.out.println (ex);
                System.exit(1);
            }
        }

        public ZookeeperClient getZookClient() {
            return zookClient;
        }
    }
   
And here is my ZookeeperClient code -

    public class ZookeeperClient {

        private CuratorFramework client;
        private String latchPath;
        private String id;
        private LeaderLatch leaderLatch;

        public ZookeeperClient(String connString, String latchPath, String id) {
            client = CuratorFrameworkFactory.newClient(connString, new 
ExponentialBackoffRetry(1000, Integer.MAX_VALUE));
            this.id = id;
            this.latchPath = latchPath;
        }

        public void start() throws Exception {
            client.start();
            client.getZookeeperClient().blockUntilConnectedOrTimedOut();
            leaderLatch = new LeaderLatch(client, latchPath, id);
            leaderLatch.start();
        }

        public boolean isLeader() {
            return leaderLatch.hasLeadership();
        }

        public Participant currentLeader() throws Exception {
            return leaderLatch.getLeader();
        }

        public void close() throws IOException {
            leaderLatch.close();
            client.close();
        }

        public CuratorFramework getClient() {
            return client;
        }

        public String getLatchPath() {
            return latchPath;
        }

        public String getId() {
            return id;
        }

        public LeaderLatch getLeaderLatch() {
            return leaderLatch;
        }
    }
   
And this is the way I am using it -

    ZookeeperLeaderTester zookClient = 
ZookeeperLeaderTester.getInstance().getZookClient();
    if (zookClient.isLeader()) {
        // then do stuff
    }