[
https://issues.apache.org/jira/browse/CURATOR-637?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Kezhu Wang reassigned CURATOR-637:
----------------------------------
Assignee: Kezhu Wang
> Get Leader zNode actual path from LeaderSelector
> ------------------------------------------------
>
> Key: CURATOR-637
> URL: https://issues.apache.org/jira/browse/CURATOR-637
> Project: Apache Curator
> Issue Type: Improvement
> Components: Recipes
> Affects Versions: 5.2.1
> Reporter: Robin Singh
> Assignee: Kezhu Wang
> Priority: Minor
> Fix For: TBD
>
>
> We are exploring LeaderSelector to implement leader election in our spring
> application. To implement fencing, we have to fetch all the participating
> zNodes in the leader election and then match the leaderSelector Id with each
> child's data.
>
> This code is being executed in a Timer.
>
> {code:java}
> if (isLeader.get()) {
> try {
> curator.createContainers("/spring-integration/fence");
> Stat stat =
> curator.checkExists().forPath("/spring-integration/leader");
> if (null != stat) {
> List<String> allChilds =
> curator.getChildren().forPath("/spring-integration/leader");
> if (allChilds != null && !allChilds.isEmpty()) {
> String myChildPath = null;
> for (String child : allChilds) {
> String childPath = "/spring-integration/leader/" +
> child;
> try {
> String childId = new
> String(curator.getData().forPath(childPath), "UTF-8");
> if (myId.equals(childId)){
> myChildPath = childPath;
>
> break;
>
> }
> } catch (Exception e){
> //ignore
> }
> }
> if (null != myChildPath){
> curator.transaction()
> .forOperations(curator.transactionOp().setData()
> .forPath("/spring-integration/fence",new String("" +
> counter.incrementAndGet()).getBytes()),
> curator.transactionOp().check().forPath(myChildPath));
>
> }
> }
> String stringData = new
> String(curator.getData().forPath("/spring-integration/fence"));
> System.out.println("SAVED DATA: " + stringData);
> }
> } catch (Exception e){
> e.printStackTrace();
> }
> } else{
> System.out.println("I am Not the leader, I cannot write anything");
> leaderSelector.requeue();
> }
> {code}
>
> AutoRequeue is disabled, we are requeing leader selection if isLeader is
> false.
>
> This is the leaderSelectorListener.
> {code:java}
>
> @Override
> public void takeLeadership(CuratorFramework client) throws Exception {
> try{
> System.out.println("I AM THE LEADER");
> isLeader.set(true);
> Thread.sleep(Long.MAX_VALUE);
> } catch (@SuppressWarnings("unused") InterruptedException e){
>
> } finally{
> System.out.println("I AM NOT THE LEADER ANYMORE");
>
> myId = generateId();
> leaderSelector.setId(myId);
> isLeader.set(false);
> }
> }
> {code}
>
> Generating a new ID so that when requeing for leaderElection, a new node will
> be generated with a different ID.
> Question 1. Do I have to re generate ID so that when requeing for
> leaderElection a new zNode will be created using that new ID? Can I assume
> that in all the scenarios the zNode will always be deleted and then only a
> new leader will be elected from the participants?
>
> Improvement 1. If only we could get the zNode path for our application using
> leaderSelection.getCurrentPath() as InterProcessMutex stores that path in
> threadData map the code for fencing would be cleaned up.
>
> I was checking some issues related to fencing and leader based dataStore. And
> from there I found this document
> [https://docs.google.com/document/d/1cBY1t0k5g1xNqzyfZby3LcPu4t-wpx57G1xf-nmWrCo/edit#]
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