Robin Singh created CURATOR-637:
-----------------------------------
Summary: 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
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.
if (isLeader.get()) {
try {
//Stat stat =
zookeeper.exists("/spring-integration/fence", false);
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)) { // checking
for my zNode
myChildPath = childPath;
break;
}
} catch (Exception e) {
//ignore
}
}
if (null != myChildPath) { // fencing, update
only if my childPath exists
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();
}
AutoRequeue is disabled, we are requeing leader selection if isLeader is false.
This is the leaderSelectorListener.
@Override
public void takeLeadership(CuratorFramework client) throws
Exception {
try {
// when this method exits, the leadership will be revoked;
// therefore this thread needs to be held up until the
// candidate is no longer leader
System.out.println("I AM THE LEADER");
isLeader.set(true);
Thread.sleep(Long.MAX_VALUE);
} catch (@SuppressWarnings("unused") InterruptedException e) {
// InterruptedException, like any other runtime exception,
// is handled by the finally block below. No need to
// reset the interrupt flag as the interrupt is handled.
} finally {
System.out.println("I AM NOT THE LEADER ANYMORE");
myId = generateId();
leaderSelector.setId(myId);
isLeader.set(false);
}
}
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() 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#
--
This message was sent by Atlassian Jira
(v8.20.7#820007)
