Clustering Conventional Brokers

There are two general methods of connecting conventional brokers into a cluster: from the command line (using the -cluster option) or by setting the imq.cluster.brokerlist property in the cluster configuration file. Whichever method you use, each broker that you start attempts to connect to the other brokers in the cluster every five seconds; the connection will succeed once the master broker is started up (if one is configured). If a broker in the cluster starts before the master broker, it will remain in a suspended state, rejecting client connections, until the master broker starts; the suspended broker then will automatically become fully functional. It is therefore a good idea to start the master broker first and then the others, after the master broker has completed its startup.

Whichever clustering method you use, you must make sure that no broker in the cluster is given an address that resolves to the network loopback IP address (127.0.0.1). Any broker configured with this address will be unable to connect to other brokers in the cluster.

In particular, some Linux installers automatically set the localhost entry to the network loopback address. On such systems, you must modify the system IP address so that all brokers in the cluster can be addressed properly: For each Linux system participating in the cluster, check the /etc/hosts file as part of cluster setup. If the system uses a static IP address, edit the /etc/hosts file to specify the correct address for localhost. If the address is registered with Domain Name Service (DNS), edit the file /etc/nsswitch.conf to change the order of the entries so that DNS lookup is performed before consulting the local hosts file. The line in /etc/nsswitch.conf should read as follows:

   hosts: dns files

If you are clustering a Message Queue 4.1 broker together with those from earlier versions of Message Queue, you must set the value of the 4.1 broker’s imq.autocreate.queue.maxNumActiveConsumers property to 1. Otherwise the brokers will not be able to establish a cluster connection.

To Cluster Conventional Brokers from the Command Line

1. If you are using a master broker, start it with the imqbrokerd command, using the -cluster option to specify the complete list of brokers to be included in the cluster.

   For example, the following command starts the broker as part of a cluster consisting of the brokers running at the default port (7676) on host1, at port 5000 on host2, and at port 9876 on the default host (localhost):

      imqbrokerd  -cluster host1,host2:5000,:9876
   

2. Once the master broker (if any) is running, start each of the other brokers in the cluster with the imqbrokerd command, using the same list of brokers with the -cluster option that you used for the master broker.

   The value specified for the -cluster option must be the same for all brokers in the cluster.

To Cluster Conventional Brokers Using a Cluster Configuration File

An alternative method, better suited for production systems, is to use a cluster configuration file to specify the composition of the cluster:

1. Create a cluster configuration file that uses the imq.cluster.brokerlist property to specify the list of brokers to be connected.

   If you are using a master broker, identify it with the imq.cluster.masterbroker property in the configuration file.

2. For each broker in the cluster, set the imq.cluster.url property in the broker’s instance configuration file to point to the cluster configuration file.

3. Use the imqbrokerd command to start each broker.

   If there is a master broker, start it first, then the others after it has completed its startup.

To Establish Secure Connections Between Brokers

If you want secure, encrypted message delivery between brokers in a cluster, configure the cluster connection service to use an SSL-based transport protocol:

1. For each broker in the cluster, set up SSL-based connection services, as described in Message Encryption.

2. Set each broker’s imq.cluster.transport property to ssl, either in the cluster configuration file or individually for each broker.