[Opensymphony-oscache] OSCache 2.1 - JGroups 2.2.7 - clustering doesn't work

As a sidenote, we had an issue with our Fedora Core 4 install that resulted in the hostname resolving to 127.0.0.1; if the code is using the name of the local host and resolving it to an IP address, and then opening up listeners on that address, this results in all of those listeners being open on 127.0.0.1 - where no amount of multicast broadcasting is ever going to yield a result.

If you encounter problems like this, make sure you run netstat -an, and look for the listener ports in LISTEN mode.  Look at the IP addresses that those services are bound to - if they look like the wrong IP address, verify that your /etc/hosts doesn't resolve your system's name - whatever it might be - to 127.0.0.1.

This will also cause the same behavioral problems with Tomcat's clustering, for example - which will cause it to open the Tomcat cluster listeners on 127.0.0.1, and no session broadcasting between servers will take place.

A bug was filed against Tomcat by us to request that they issue a WARN or ERROR entry in the logs when they discover that getHost()/getAddress() results in a loopback IP address in 127; if you discover that you have encountered the same problem as we did in jGroups, you could file a bug against them requesting the same, to make these problems easier to diagnose in the future.

Happy camping,
Greg

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