Pro Tips: Run Multiple Jenkins CI Servers on a Single Machine

Jenkins (or Hudson if you work for Oracle) is a great, simple and steady continuous integration and build server.  One of its greatest features is that despite being packaged as a standard .war ready to be dropped into your JEE web container of choice … it also contains an embedded web container that makes the .war everything you need in most situations.  Simply run

java -jar jenkins.war

and up starts Jenkins on port 8080 in all of its glory.  All of Jenkins’ configuration files, plugins, and working directories go under <USER_HOME>/.jenkins by default.  Perfect.

Except if you want to run multiple instances on the same machine.  We are going to get a config folder collision.  It turns out this is a piece of cake, but the docs are hard to find.  Jenkins will use a JENKINS_HOME path environement variable for its configuration files if one is set so a simple change means we can run Jenkins out of any directory we desire:

java -DJENKINS_HOME=/path/to/configs -jar jenkins.war

What about the port you say?  Winston, the embedded web container used, has a simple property for this too:

java -DJENKINS_HOME=/path/to/configs -jar jenkins.war --httpPort=9090