Creating a custom JGroups channel for a cluster

[mylos78]

Hi all !

I would like to know if it's possible to define a new WildFly cluster channel (besides "ejb" and "web") somehow, so that for example I can use it just for my web application. Any way to do it with management interfaces or programmatically ?

Thanks

Mylos

[pferraro]

In WildFly 8, the JGroups subsystem defines protocol stacks, from which channels can be built.  Each protocol stack exposes a ChannelFactory, from which new channel can easily be created programmatically.

In WF8, you can create/connect a channel named "foo", with a cluster name "cluster" that uses the "udp" stack using a service activator:

public class ChannelServiceActivator implements org.jboss.msc.service.ServiceActivator {
    @Override
    public void activate(ServiceActivatorContext context) {
        ServiceName name = ServiceName.of(...);
        InjectedValue<ChannelFactory> factory = new InjectedValue<>();
        context.getServiceTarget().addService(name, new MyService(factory))
                .addDependency(ChannelFactoryService.getServiceName("udp"), ChannelFactory.class, factory)
                .install();
    }
}

public class MyService implements org.jboss.msc.service.Service<Channel> {
    private final Value<ChannelFactory> factory;
    private volatile Channel channel;

    public MyService(Value<ChannelFactory> factory) {
        this.factory = factory;
    }

    @Override
    public Channel getValue() {
        this.channel = channel;
    }

    @Override
    public void start(StartContext context) {
        this.channel = this.factory.getValue().createChannel("foo");
        this.channel.connect("cluster");
    }

    @Override
    public void stop(StopContext context) {
        this.channel.disconnect();
        this.channel.close();
        this.channel = null;
    }
}

WildFly 9 will add the ability to declaratively define channels as well as fork channels (see http://www.jgroups.org/manual/index.html#ForkChannel) and inject them into your application via JNDI.  Fork channels are particularly useful for allowing multiple services (including Infinispan caches) to share a channel instance.

To create a JGroups channel in WF9 (master), the service activator instrumentation used in the WF8 example is completely unnecessary.  You can either define a new channel directly in the subsystem and inject it into your application, or inject the ChannelFactory and create/connect the channel programmatically.

e.g.

<subsystem xmlns="urn:jboss:domain:jgroups:3.0">
    <channels default="ee">
        <channel name="ee"/>
        <channel name="foo"/>
    </channels>
    <stacks default="udp">
        <stack name="udp">
            <!-- ... -->
        </stack>
   </stacks>
</subsystem>

As always, anything declarable via the domain configuration xml is definable via the management API.

You can either inject the "foo" channel directly:

@Resource(lookup = "java:jboss/jgroups/channel/foo")
private Channel channel;

@PostConstruct
public void init() {
    this.channel.connect("cluster");
}

@PreDestroy
public void destroy() {
    this.channel.disconnect();
}

... or inject the channel factory and create the channel manually, e.g.

@Resource(lookup = "java:jboss/jgroups/factory/default") // "default" refers to the default stack
private ChannelFactory factory;
private Channel channel;

@PostConstruct
public void init() {
    this.channel = this.factory.createChannel("foo");
    this.channel.connect("cluster");
}

@PreDestroy
public void destroy() {
    this.channel.disconnect();
    this.channel.close();
}

In subsequent WF9 releases, you'll be able to define and create fork channels in a similar way, where a ChannelFactory is exposed both per <stack/> (to create a JChannel) and per <channel/> (to create a ForkChannel).  That work is here, and is awaiting merge:

WFLY-4105 Add support for explicit fork channel protocols by pferraro · Pull Request #6992 · wildfly/wildfly · GitHub

[mylos78]

Thank you very much for the valuable and authoritative reply Paul!

[java.food]

I tried using this approach with WF 9 and 10 (in both standalone and domain configuration), but I am not having any success.  First of all, there is no java:jboss/jgroups/channel/<channel name> or java:jboss/jgroups/factory/default in JNDI.  However, there is a java:jboss/jgroups/factory/udp.  However, java:jboss/jgroups/factory/udp is of JChannelFactory type, not ChannelFactory type.  Are there other configuration changes need to be done in order for this approach to work?

[pferraro]

java.food Can you post the code you are trying to use?