Recently (in a project) we were required to determine the master node from a pool of similar type of nodes. And if master node fails, any other node should take on the responsibility – so that the service remains available.
\nSo, the use-case was something like – Only single node should behave as a master node and it will coordinate with all the worker nodes to process the required tasks.<\/p>\n
Clearly, it\u2019s a leader-election recipe. This is supported in Curator\/Zookeeper API, but we found it little complex in terms of blocking the threads to claim the leadership for a longer duration. Otherwise, it was not functioning well.<\/p>\n
So, we figured out a very simple way to determine the master node. Here are the steps below:<\/p>\n
[code]
\npublic static boolean isMasterCoordinatorNode(String nodeId) throws Exception {
\n List<String> coordinatorNodes = getCuratorClient().getChildren().forPath("my\/project\/coordinators");
\n if (coordinatorNodes!=null && coordinatorNodes.size()>0)
\n {
\n TreeSet<String> set = new TreeSet<String>(coordinatorNodes);
\n String firstNodeId = set.first();
\n if(firstNodeId.equals(nodeId)){
\n return true;
\n }
\n }
\n return false;
\n }<\/p>\n
public synchronized static CuratorFramework getCuratorClient(){
\n if(_client == null){
\n String zookeeperStr = "127.0.0.1:2181"; \/\/ zookeeper address
\n RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
\n _client = CuratorFrameworkFactory.newClient(zookeeperStr, retryPolicy);
\n _client.start();
\n }
\n return _client;
\n }
\n[\/code]<\/p>\n<\/li>\n<\/ul>\n<\/li>\n
In our case this worked very well. \ud83d\ude42<\/p>\n