org.adroitlogic.ultraesb.api.mediation

Interface ClusterSupport

public interface ClusterSupport

The cluster and group co-ordination related functionality.

Since:

2.1.0

Author:

Ruwan

Method Summary

Methods

Modifier and Type	Method and Description
boolean	canFailover(String nodeName) Can this node act as the failover node for the given node name
int	getActiveNodeCount() Gives the number of active nodes in the current nodes cluster domain
List<String>	getActiveNodeNames() Gives the node names of the active nodes in the current nodes cluster domain
List<String>	getCurrentlyActingAsNodeGroups() Gives the acting as node group list that this node is currently acting as
List<String>	getCurrentlyActingAsNodes() Gives the acting as node name list that this node is currently acting as
String	getDomain() Gives the cluster domain of the cluster, if clustering is enabled
List<String>	getFailoverNodeNames() Gives the list of node names to which this node provides failover facility
String	getNodeName() Gives the node name of this node in the cluster domain
String	getQualifiedSessionId() Gives the current session of this node in the cluster domain in the form of, $DOMAIN:$NODE_NAME:$SESSION_ID where the $DOMAIN is getDomain() $NODE_NAME is getNodeName() $SESSION_ID is the current local session id of this node in the cluster
boolean	isActingAs(String nodeName) Is this node acting as the given node
boolean	isAlive() Checks whether the node is connected to the cluster or not.
boolean	isClustered() Checks whether the clustering is enabled or not
int	nextSequenceNumber(String path) Gets a distributed continuously increasing sequence number for the given path.
String	publishCommand(ControlCommand command) Publishes a ControlCommand into the complete cluster.
void	releaseLock(String path) Release any distributed locks for the given path, and tries to deletes the path itself.
boolean	tryLock(String path) This methods never blocks or wait to acquire the lock.
void	unwatchActiveNodes(NodeWatcher watcher) Un-register the previously registered node watcher, it is unregistered at the functional level, where your NodeWatcher will not get any further notifications from this point onwards.
void	watchActiveNodes(NodeWatcher watcher) Watches the active nodes space and notify the provided node watcher in-case of a node leaving the cluster or new node joining the cluster.

Method Detail

isClustered

boolean isClustered()

Checks whether the clustering is enabled or not

Returns:

true if clustering is enabled, false otherwise

isAlive

boolean isAlive()

Checks whether the node is connected to the cluster or not. This method may return false in-case of a failure to establish a session with the ZooKeeper, or in-case of a network failure which result in the ZooKeeper connection to be dropped, or if the ZooKeeper quorum is down resulting the connections by ZooKeeper clients (like ClusterManager) to terminate there connections

Returns:

whether the cluster is connected or not

getDomain

String getDomain()

Gives the cluster domain of the cluster, if clustering is enabled

Returns:

the cluster domain

getNodeName

String getNodeName()

Gives the node name of this node in the cluster domain

Returns:

the name of this node in the cluster domain

getQualifiedSessionId

String getQualifiedSessionId()

Gives the current session of this node in the cluster domain in the form of, $DOMAIN:$NODE_NAME:$SESSION_ID where the

• $DOMAIN is getDomain()
• $NODE_NAME is getNodeName()
• $SESSION_ID is the current local session id of this node in the cluster

Returns:

the current session identifier of the node in the cluster

getActiveNodeNames

List<String> getActiveNodeNames()

Gives the node names of the active nodes in the current nodes cluster domain

Returns:

the list of active node names

getActiveNodeCount

int getActiveNodeCount()

Gives the number of active nodes in the current nodes cluster domain

Returns:

the number of active nodes in the domain

getCurrentlyActingAsNodes

List<String> getCurrentlyActingAsNodes()

Gives the acting as node name list that this node is currently acting as

Returns:

the currently acting as node name list

getCurrentlyActingAsNodeGroups

List<String> getCurrentlyActingAsNodeGroups()

Gives the acting as node group list that this node is currently acting as

Returns:

the currently acting as node group list excluding this node's node group

getFailoverNodeNames

List<String> getFailoverNodeNames()

Gives the list of node names to which this node provides failover facility

Returns:

the list of nodes that this node acts as a failover hop

isActingAs

boolean isActingAs(String nodeName)

Is this node acting as the given node

Parameters:

nodeName - the node name to check the acting as

Returns:

true of the given node name is being acted by this node

canFailover

boolean canFailover(String nodeName)

Can this node act as the failover node for the given node name

Parameters:

nodeName - the node name to test for failover

Returns:

true if this node is a failover hop for the given node name

tryLock

boolean tryLock(String path)

This methods never blocks or wait to acquire the lock. Try to lock the given path, if successful boolean true will be returned, if not acquired false will be returned.

This method doesn't guarantee to acquire the lock, if the lock can be acquired it does so but do not wait and try to acquire it again and again. Should be useful in cases where you need a distributed access to a single location. The path can be a hierarchical path where the '/' being the path delimiter. However locks are not hierarchical meaning that getting a lock at path messages/db doesn't block another user from taking a lock at path messages/db/foo.

Any successful lock acquired by this method should be released as sooner as possible to let any other node take the lock. However any lock miss (that is a false return from this method will clear the lock nodes created to try to acquire the lock within its protocol). Hence the usage pattern of this method should happen within a try-finally block as shown below

String path = "messages/db/foo"; boolean lockAcquired; try { lockAcquired = mediation.getClusterSupport().tryLock(path); if (lockAcquired) { // do the processing with the lock } } catch(Exception e) { // exception handling } finally { if (lockAcquired) { mediation.getClusterSupport().releaseLock(path); } }

Parameters:

path - the global path representing the lock

Returns:

true if the lock is acquired, false if it is already acquired by somebody else or in case of an error

releaseLock

void releaseLock(String path)

Release any distributed locks for the given path, and tries to deletes the path itself. However this method doesn't guarantee to delete the path. Should be used with tryLockPath method to make sure the lock cleanup works to some extent.

Parameters:

path - the path for which the lock to be released

publishCommand

String publishCommand(ControlCommand command)

Publishes a ControlCommand into the complete cluster. Note that the publishing node will also execute this command via the command execution framework.

Parameters:

command - the command to be executed by the cluster

Returns:

the path at which the command is being published at

watchActiveNodes

void watchActiveNodes(NodeWatcher watcher)

Watches the active nodes space and notify the provided node watcher in-case of a node leaving the cluster or new node joining the cluster. The watch process is continuous as in once you register the NodeWatcher, then that watcher will be notified for all active node list changes until the user calls, unwatchActiveNodes(org.adroitlogic.ultraesb.api.mediation.helper.NodeWatcher). You may call this method more than once with different NodeWatcher references.

Parameters:

watcher - the watcher to be notified.

unwatchActiveNodes

void unwatchActiveNodes(NodeWatcher watcher)

Un-register the previously registered node watcher, it is unregistered at the functional level, where your NodeWatcher will not get any further notifications from this point onwards.

Parameters:

watcher - the watcher to be un-registered

nextSequenceNumber

int nextSequenceNumber(String path)

Gets a distributed continuously increasing sequence number for the given path. For a specific path it is guaranteed to give a continuously increasing number which is bound by Integer.MAX_VALUE

Parameters:

path - the path to which the sequence number is generated

Returns:

the generated sequence number for the given path