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< title > ActiveMQ Clustering with JGroups Example< / title >
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< h1 > ActiveMQ Clustering with JGroups Example< / h1 >
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< p > This example demonstrates the working of a two node cluster using JGroups as the underlying topology broadcasting/discovery
technique.< / p >
< p > We deploy a queue on to the cluster, then create a consumer on the queue on each node, and we create a producer on only one of the nodes.< / p >
< p > We then send some messages via the producer, and we verify that < b > both< / b > consumers receive the sent messages
in a round-robin fashion.< / p >
< p > This example uses JNDI to lookup the JMS Queue and ConnectionFactory objects. If you prefer not to use
JNDI, these could be instantiated directly.< / p >
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< p > To enable ActiveMQ to use JGroups you need to configure JGroups configuration file and make sure it is on the classpath
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by placing in the configuration directory, the file test-jgroups-file_ping.xml is the configuration used in this
exaample< / p >
< p > You then configure the jgroups file used by the broadcast and discovery groups in the configuration along with the
channel name which you want this cluster to share.< / p >
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< broadcast-groups>
< broadcast-group name="my-broadcast-group">
< broadcast-period>5000< /broadcast-period>
< jgroups-file>test-jgroups-file_ping.xml< /jgroups-file>
< jgroups-channel>hornetq_broadcast_channel< /jgroups-channel>
< connector-ref>netty-connector< /connector-ref>
< /broadcast-group>
< /broadcast-groups>
< discovery-groups>
< discovery-group name="my-discovery-group">
< jgroups-file>test-jgroups-file_ping.xml< /jgroups-file>
< jgroups-channel>hornetq_broadcast_channel< /jgroups-channel>
< refresh-timeout>10000< /refresh-timeout>
< /discovery-group>
< /discovery-groups>
< / code >
< / pre >
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< p > For more information on ActiveMQ clustering in general, please see the clustering
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section of the user manual.< / p >
< h2 > Example step-by-step< / h2 >
< p > < i > To run the example, simply type < code > ./build.sh< / code > (or < code > build.bat< / code > on windows) from this directory< / i > < / p >
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< li > Get an initial context for looking up JNDI from server 0.< / li >
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ic0 = getContext(0);
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< li > Look-up the JMS Queue object from JNDI< / li >
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< code > Queue queue = (Queue)ic0.lookup("/queue/exampleQueue");< / code >
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< li > Look-up a JMS Connection Factory object from JNDI on server 0< / li >
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< code > ConnectionFactory cf0 = (ConnectionFactory)ic0.lookup("/ConnectionFactory");< / code >
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< li > Get an initial context for looking up JNDI from server 1.< / li >
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< code > ic1 = getContext(1);< / code >
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< li > Look-up a JMS Connection Factory object from JNDI on server 1< / li >
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< code > ConnectionFactory cf1 = (ConnectionFactory)ic1.lookup("/ConnectionFactory");
< / code >
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< li > We create a JMS Connection connection0 which is a connection to server 0< / li >
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connection0 = cf0.createConnection();
< / code >
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< li > We create a JMS Connection connection1 which is a connection to server 1< / li >
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connection1 = cf1.createConnection();
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< li > We create a JMS Session on server 0< / li >
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Session session0 = connection0.createSession(false, Session.AUTO_ACKNOWLEDGE);
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< li > We create a JMS Session on server 1< / li >
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Session session1 = connection1.createSession(false, Session.AUTO_ACKNOWLEDGE);
< / code >
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< li > We start the connections to ensure delivery occurs on them< / li >
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connection0.start();
connection1.start();
< / code >
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< li > We create JMS MessageConsumer objects on server 0 and server 1< / li >
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< code >
MessageConsumer consumer0 = session0.createConsumer(queue);
MessageConsumer consumer1 = session1.createConsumer(queue);
< / code >
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< li > We create a JMS MessageProducer object on server 0.< / li >
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MessageProducer producer = session0.createProducer(queue);< / code >
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< li > We send some messages to server 0.< / li >
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final int numMessages = 10;
for (int i = 0; i < numMessages ; i + + )
{
TextMessage message = session0.createTextMessage("This is text message " + i);
producer.send(message);
System.out.println("Sent message: " + message.getText());
}
< / code >
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< li > We now consume those messages on *both* server 0 and server 1.
We note the messages have been distributed between servers in a round robin fashion.
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ActiveMQ has < b > load balanced< / b > the messages between the available consumers on the different nodes.
ActiveMQ can be configured to always load balance messages to all nodes, or to only balance messages
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to nodes which have consumers with no or matching selectors. See the user manual for more details.< / li >
JMS Queues implement point-to-point message where each message is only ever consumed by a
maximum of one consumer.
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for (int i = 0; i < numMessages ; i + = 2 )
{
TextMessage message0 = (TextMessage)consumer0.receive(5000);
System.out.println("Got message: " + message0.getText() + " from node 0");
TextMessage message1 = (TextMessage)consumer1.receive(5000);
System.out.println("Got message: " + message1.getText() + " from node 1");
}
< / code >
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< li > And finally (no pun intended), < b > always< / b > remember to close your JMS resources after use, in a < code > finally< / code > block. Closing a JMS connection will automatically close all of its sessions, consumers, producer and browser objects< / li >
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finally
{
if (connection0 != null)
{
connection0.close();
}
if (connection1 != null)
{
connection1.close();
}
}
< / code >
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