[
https://issues.apache.org/jira/browse/CURATOR-637?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Robin Singh updated CURATOR-637:
--------------------------------
Description:
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 {
//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(); }
{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
{ // 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);
}
}
{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() 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#]
was:
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#
> 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
> 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 {
> //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(); }
> {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
> { // 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);
> }
> }
> {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() 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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