In a recent project, I am using a java daemon to manage and pool connections to an XML service I am using. If the connection fails, the daemon automatically closes the socket and reconnects. This was working great until one day the IP addresses for the service changed. Though TTL for the dns lookup had run out and the local dns properly found the new IP’s, the connection pool was still not able to make connections until the JRE and daemon were restarted.

I thought this was really weird, and did some research. It turns out that Sun’s JRE has it’s own dns cache that defaults to “cache forever.” Though, I think this is a really bad default behavior, they do provide a way to fix it. It turns out there are some properties that can be set on the command line to change it as documented in their Networking Properties manual. If you pass a ** **to the JRE commandline with the number of seconds to cache, that should fix it. Sun’s argument for having this default value is to hedge against DNS spoofing attacks, but if you consider your dns to be relatively secure, it can be just an annoyance.