Multiple JChannels in one cluster

Question

I thought that it is easily possible to have multiple JChannels (with different names) in the same cluster. I have to following setup:

@Singleton
public class ChannelOne extends ReceiverAdapter
{
    JChannel channel;

    public void start()
    {
        channel = new JChannel();

        channel.setReceiver(this);
        channel.connect("ChannelOne");
    }

    public void receive(Message msg)
    {
        DataObject data = (DataObject) msg.getObject();
        log.debug("JGroups: Message received event received: " + data.eventData);
    }

    public void send(DataObject data)
    {
        Message msg = new Message(null, null, data);
        log.debug("JGroups: send: " + data.eventData);
        channel.send(msg);
    }

    public void viewAccepted(View new_view)
    {
        log.debug("JGroups: View accepted: " + new_view);
    }

}

And my JGroups configuration is the following (it is used on openshift, where we cannot use UDP! - How to open a JChannel (JGroups) using Openshift Wildfly 8 Cartridge )

<config xmlns="urn:org:jgroups"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="urn:org:jgroups http://www.jgroups.org/schema/JGroups-3.3.xsd">
    <TCP
            external_addr="${env.OPENSHIFT_GEAR_DNS}"
            external_port="${env.OPENSHIFT_WILDFLY_CLUSTER_PROXY_PORT}"
            bind_port="${env.OPENSHIFT_WILDFLY_CLUSTER_PORT}"
            bind_addr="${env.OPENSHIFT_WILDFLY_IP}"
            defer_client_bind_addr="true"
            enable_diagnostics="false"/>

    <TCPPING timeout="3000"
             initial_hosts="${env.OPENSHIFT_WILDFLY_CLUSTER}"
             port_range="0"
             num_initial_members="1"/>
    <MERGE2/>
    <FD/>
    <VERIFY_SUSPECT/>
    <BARRIER/>
    <pbcast.NAKACK2
            use_mcast_xmit="false"/>
    <UNICAST3/>
    <pbcast.STABLE/>
    <pbcast.GMS/>
    <MFC/>
    <FRAG2/>
</config>

Now assume that we have not only a ChannelOne but also a ChannelTwo Singleton with the goal to seperate events by their usage.

If I do so, I observe that the messages are not all received correctly. There seems to be a mix between the two channels. I have a plenty of warnings in the log that messages have been dropped.

What do I understand wrong in this concept of Channels?

Answer 1

A channel is an endpoint into a cluster. If you have different applications using different clusters you need to separate the clusters, or else the apps will receive each other's messages.

To do this, pick different ports ( external_port , bind_port ) for the different clusters.

Answer 2

This is the "ping" mechanism we use with WF/EAP on OpenShift:

• https://github.com/jboss-openshift/openshift-ping/blob/master/kube/src/main/java/org/openshift/ping/kube/KubePing.java

Should be easy to configure and use.

Note: authorization must be granted to the service account the pod is running under to be allowed to access Kubernetes' REST api.