If I start up a single instance of the broker on a loopback address I get the following:
[05/Sep/2014:16:45:11 BST] WARNING [B3236]: Bad bind address of portmapper service for cluster, please change imq.portmapper.hostname: Loopback IP address is not allowed in broker address localhost[localhost/127.0.0.1] for cluster
[05/Sep/2014:16:45:11 BST] WARNING [B1137]: Cluster initialization failed. Disabling the cluster service.
I have a setup (actually the Azure Compute Emulator) which allows multiple vms/processes to be started up with their own unique ipaddresses of the form 127.X.X.X which are actually loopback addresses as far as java.net.InetAddress is concenrned. Therefore despite the fact that I am successfully using these addresses for socket to socket communication between those vm/processes I cannot use them to run an OpenMq cluster.
As a work around I have set up the brokers to bind to a SINGLE non loopback address and use different ports and that works. So it's not the case that you can't cluster on one ipaddress.
Why was loopback disallowed? If it is theoretically possible, is there a setting to enable it for clustering?
According to Amy Kang of Oracle opnenmq users mailing list this is by design since clustering is intended to be across muultiple servers. You can however bind several brokers to one non loopback address and use different ports.