Best practices for deploying Java webapps with minimal downtime?

Question

When deploying a large Java webapp (>100 MB .war) I\'m currently use the following deployment process:

• The application .war file is expanded locally on the develop

Answer 1

Tomcat 7 has a nice feature called "parallel deployment" that is designed for this use case.

The gist is that you expand the .war into a directory, either directly under webapps/ or symlinked. Successive versions of the application are in directories named app##version, for example myapp##001 and myapp##002. Tomcat will handle existing sessions going to the old version, and new sessions going to the new version.

The catch is that you have to be very careful with PermGen leaks. This is especially true with Grails that uses a lot of PermGen. VisualVM is your friend.