The Java Gotcha for Data Centre Relocations

Way back in time, someone thought it would be a good idea for the Java run-time to cache DNS look-ups itself. Once it has an IP address for a name, it doesn't look up the name again for the duration of the Java run-time process.

Fast forward a decade, and the Java run-time is the foundation of many web sites. It sits there running, and caches DNS lookups as long as the web site is up.

On my current project, we're changing the IP address of every device we move, which is typical for a data centre relocation. We have a number of Java-based platforms, and they're well integrated (read interconnected) with the rest of our environment, and we're finding we have to take an outage to restart the Jave-based platforms far too often.

In hindsight, it would have been far simpler to change the Java property to disable DNS caching. Run this way for a while in the old environment to be sure there are no issues (highly unlikely, but better safe than sorry). Then you can start moving and changing IPs of other devices knowing your Java-based applications will automatically pick up the changes you make in DNS.

In case the link above goes stale, the four properties you want to look at are:

networkaddress.cache.ttl
networkaddress.cache.negative.ttl
sun.net.inetaddr.ttl
sun.net.inetaddr.negative.ttl

Look them up in your Java documentation and decide which caching option works best for you. (Normally I'd say how to set the parameters, but I've never done Java and I fear I'd say something wrong.)