com.aquenos.cassandra.pvarchiver.server.cluster

Class ClusterManagementService

java.lang.Object

com.aquenos.cassandra.pvarchiver.server.cluster.ClusterManagementService

All Implemented Interfaces:

Aware, DisposableBean, InitializingBean, SmartInitializingSingleton, ApplicationEventPublisherAware

public class ClusterManagementService
extends Object
implements ApplicationEventPublisherAware, DisposableBean, InitializingBean, SmartInitializingSingleton

Manages the cluster of archive servers. This class takes care of registering the server in the cluster and periodically updating its online state so that other servers can detect it as being online.

The isOnline() method can be used to check whether this server is currently online. Components that are interested in this information can also register as ApplicationListeners listening for the ServerOnlineStatusEvent. As event notification is performed in an asynchronous way, calls to the isOnline() method may reflect an updated online status before the corresponding event is received. Please note that listeners that are registered after events have been sent will only be notified when the status changes again. Therefore, when registering a new listener, the listener should query the current state explicitly because it might not receive an event with this state.

Author:

Sebastian Marsching

Field Summary

Fields

Modifier and Type	Field and Description
protected org.apache.commons.logging.Log	log Logger for this class.

Constructor Summary

Constructors

Constructor and Description
ClusterManagementService()

Method Summary

Modifier and Type	Method and Description
void	afterPropertiesSet()
void	afterSingletonsInstantiated()
void	destroy()
String	getInterNodeCommunicationUrl(UUID serverId) Returns the inter-node communication URL for the specified server.
ServerStatus	getServer(UUID serverId) Returns the status for the server with the specified ID.
List<ServerStatus>	getServers() Returns the status for all servers in the cluster.
ServerStatus	getThisServer() Returns the current status of this server.
boolean	isOnline() Returns true if the server is currently considered online (has recently registered itself in the Cassandra database), false otherwise.
void	onClusterServersDAOInitializedEvent(ClusterServersDAOInitializedEvent event) Handles the ClusterServersDAOInitializedEvent.
void	onInterNodeCommunicationServiceInitializedEvent(InterNodeCommunicationServiceInitializedEvent event) Handles the InterNodeCommunicationServiceInitializedEvent.
void	removeServer(UUID serverId) Removes the server with the specified ID from the cluster.
void	setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher)
void	setClusterServersDAO(ClusterServersDAO clusterServersDAO) Sets the cluster-servers DAO that is used for accessing the database.
void	setControlSystemSupportRegistry(ControlSystemSupportRegistry controlSystemSupportRegistry) Sets the control-system support registry.
void	setInterNodeCommunicationService(InterNodeCommunicationService interNodeCommunicationService) Sets the inter-node communication service.
void	setServerProperties(ServerProperties serverProperties) Sets the server-specific configuration properties.
ListenableFuture<Boolean>	verifyServerOffline(UUID serverId) Verifies that a server is actually offline.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

log

protected final org.apache.commons.logging.Log log

Logger for this class.

Constructor Detail

ClusterManagementService

public ClusterManagementService()

Method Detail

afterPropertiesSet

public void afterPropertiesSet()
                        throws Exception

Specified by:

afterPropertiesSet in interface InitializingBean

Throws:

Exception

afterSingletonsInstantiated

public void afterSingletonsInstantiated()

Specified by:

afterSingletonsInstantiated in interface SmartInitializingSingleton

destroy

public void destroy()
             throws Exception

Specified by:

destroy in interface DisposableBean

Throws:

Exception

onClusterServersDAOInitializedEvent

@EventListener
public void onClusterServersDAOInitializedEvent(ClusterServersDAOInitializedEvent event)

Handles the ClusterServersDAOInitializedEvent. This event signals that the cluster servers DAO needed by this service is ready for operation. This service uses this information in order to start the registration process that registers this server in the cluster and eventually switch to the online state, if the registration attempt is successful.

Parameters:

event - event signaling that the cluster servers DAO is ready for operation.

onInterNodeCommunicationServiceInitializedEvent

@EventListener
public void onInterNodeCommunicationServiceInitializedEvent(InterNodeCommunicationServiceInitializedEvent event)

Handles the InterNodeCommunicationServiceInitializedEvent. This event signals that the inter-node communication service needed by this service is ready for operation. This service uses this information in order start its internal clock-skew monitor (which depends on remote communication) and subsequently switch to the online state, if all other conditions are met as well.

Parameters:

event - event signaling that the inter-node communication service is ready for operation.

setApplicationEventPublisher

public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher)

Specified by:

setApplicationEventPublisher in interface ApplicationEventPublisherAware

setClusterServersDAO

@Autowired
public void setClusterServersDAO(ClusterServersDAO clusterServersDAO)

Sets the cluster-servers DAO that is used for accessing the database. Typically, this method is called automatically by the Spring container.

Parameters:

clusterServersDAO - cluster-server DAO for accessing the database.

setControlSystemSupportRegistry

@Autowired
public void setControlSystemSupportRegistry(ControlSystemSupportRegistry controlSystemSupportRegistry)

Sets the control-system support registry. The cluster management service waits for the control-system support registry to become available before switching the server online. Typically, this method is called automatically by the Spring container.

Parameters:

controlSystemSupportRegistry - control-system support registry for this archiving server.

setInterNodeCommunicationService

@Autowired
public void setInterNodeCommunicationService(InterNodeCommunicationService interNodeCommunicationService)

Sets the inter-node communication service. The inter-node communication service is needed to communicate with other servers in order to compare the system time and trigger a warning (or shutdown) when a significant clock skew is detected. Typically, this method is called automatically by the Spring container.

Parameters:

interNodeCommunicationService - inter-node communication service.

setServerProperties

@Autowired
public void setServerProperties(ServerProperties serverProperties)

Sets the server-specific configuration properties. These server properties are used when building the web-service URL at which this server is available when registering this server with the cluster.

Parameters:

serverProperties - configuration properties used by this server.

getInterNodeCommunicationUrl

public String getInterNodeCommunicationUrl(UUID serverId)

Returns the inter-node communication URL for the specified server. This is the URL that is contacted by the InterNodeCommunicationService in order to communicate with that server.

If the specified server ID is unknown of if the server is not online, null is returned.

This service serves the query from an internal cache. For this reason, the information returned might be outdated. However, this has the advantage that this method will never block.

Parameters:

serverId - ID of the server for which the inter-node communication URL shall be returned.

Returns:

inter-node communication URL for the specified server or null if the specified server ID is unknown or the server is considered offline.

Throws:

NullPointerException - if serverId is null.

getServer

public ServerStatus getServer(UUID serverId)

Returns the status for the server with the specified ID. The status is retrieved from a cache that is updated periodically. Therefore, it might be outdated. Code that needs to ensure that a server is offline should use the verifyServerOffline(UUID) method which bypasses the cache.

By using the cache, this method ensures that it will never block.

Parameters:

serverId - unique identifier identifying the server.

Returns:

current status of the server (possibly cached) or null if no status information is available for the specified ID.

Throws:

NullPointerException - if serverId is null.

getServers

public List<ServerStatus> getServers()

Returns the status for all servers in the cluster. The list is ordered by the server IDs. The status is retrieved from a cache that is updated periodically. Therefore, it might be outdated. Code that needs to ensure that a server is offline should use the verifyServerOffline(UUID) method which bypasses the cache.

By using the cache, this method ensures that it will never block.

Returns:

list of all servers in the cluster (never null).

getThisServer

public ServerStatus getThisServer()

Returns the current status of this server. Unlike the information returned by getServer(UUID), this reflects this server's actual state and does not involve caching. In particular, the online information returned with the server status reflects the current return value of isOnline().

Returns:

server status for this server (never null).

isOnline

public boolean isOnline()

Returns true if the server is currently considered online (has recently registered itself in the Cassandra database), false otherwise. In general, other components should only run actions that might interfer with the operation of other servers when this server has been registered in the database and thus this method returns true.

Returns:

true if this server is considered online, false otherwise.

removeServer

public void removeServer(UUID serverId)

Removes the server with the specified ID from the cluster. A server can only be removed if it has been offline for a sufficient amount of time. This method calls verifyServerOffline(UUID) to check that. This method does not take care of resources associated with the specified server (e.g. channels). The calling code should move such resources to a different server before removing a server.

This method blocks while it is waiting for the verification of the server's offline status and the removal of the server to finish.

Parameters:

serverId - unique identifier identifying the server to be removed.

Throws:

IllegalArgumentException - if the specified server cannot be deleted because it has not been offline for a sufficient amount of time.

RuntimeException - if there is an error accessing the underlying database.

verifyServerOffline

public ListenableFuture<Boolean> verifyServerOffline(UUID serverId)

Verifies that a server is actually offline. In contrast to the online state returned by getServer(UUID), this method does not use a cache, but always queries the database directly. The result is returned through a future so that this method does not block. If there is an error, the future's get() method throws an exception.

Parameters:

serverId - unique identifier of the server which should be checked.

Returns:

online status of the specified server exposed through a listenable future. The future returns true if the server is currently not online or if there is no status information for the specified ID in the database and false if the server with the specified ID is online.