[
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 {
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#]
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.
{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() 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 {
> 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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