org.apache.twill.discovery

Class ZKDiscoveryService

java.lang.Object

org.apache.twill.discovery.ZKDiscoveryService

All Implemented Interfaces:

AutoCloseable, DiscoveryService, DiscoveryServiceClient

public class ZKDiscoveryService
extends Object
implements DiscoveryService, DiscoveryServiceClient, AutoCloseable

Zookeeper implementation of DiscoveryService and DiscoveryServiceClient.

Discoverable services are registered within Zookeeper under the namespace 'discoverable' by default. If you would like to change the namespace under which the services are registered then you can pass in the namespace during construction of ZKDiscoveryService.

Following is a simple example of how ZKDiscoveryService can be used for registering services and also for discovering the registered services.

     

     DiscoveryService service = new ZKDiscoveryService(zkClient);
     service.register(new Discoverable() {
       @Override
       public String getName() {
         return 'service-name';
       }

       @Override
       public InetSocketAddress getSocketAddress() {
         return new InetSocketAddress(hostname, port);
       }
     });
     ...
     ...
     ServiceDiscovered services = service.discovery("service-name");
     ...
     
   

Constructor Summary

Constructors

Constructor and Description
ZKDiscoveryService(ZKClient zkClient) Constructs ZKDiscoveryService using the provided zookeeper client for storing service registry.
ZKDiscoveryService(ZKClient zkClient, String namespace) Constructs ZKDiscoveryService using the provided zookeeper client for storing service registry under namespace.

Method Summary

Modifier and Type	Method and Description
void	close()
ServiceDiscovered	discover(String service) Discover service with the given name.
Cancellable	register(Discoverable discoverable) Registers a Discoverable in zookeeper.

Methods inherited from class java.lang.Object

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

Constructor Detail

ZKDiscoveryService

public ZKDiscoveryService(ZKClient zkClient)

Constructs ZKDiscoveryService using the provided zookeeper client for storing service registry.

Parameters:

zkClient - The ZKClient for interacting with zookeeper.

ZKDiscoveryService

public ZKDiscoveryService(ZKClient zkClient,
                          String namespace)

Constructs ZKDiscoveryService using the provided zookeeper client for storing service registry under namespace.

Parameters:

zkClient - of zookeeper quorum

namespace - under which the service registered would be stored in zookeeper. If namespace is null, no namespace will be used.

Method Detail

register

public Cancellable register(Discoverable discoverable)

Registers a Discoverable in zookeeper.

Registering a Discoverable will create a node <base>/<service-name> in zookeeper as a ephemeral node. If the node already exists (timeout associated with emphemeral node creation), then a runtime exception is thrown to make sure that a service with an intent to register is not started without registering. When a runtime exception is thrown, expectation is that the process being started will fail and would be started again by the monitoring service.

Specified by:

register in interface DiscoveryService

Parameters:

discoverable - Information of the service provider that could be discovered.

Returns:

An instance of Cancellable

discover

public ServiceDiscovered discover(String service)

Description copied from interface: DiscoveryServiceClient

Discover service with the given name.

Specified by:

discover in interface DiscoveryServiceClient

Parameters:

service - Name of the service

Returns:

A ServiceDiscovered object representing the result.

close

public void close()

Specified by:

close in interface AutoCloseable