How do you remotely update Java applications?

Question

We\'ve got a Java server application that runs on a number of computers, all connected to the Internet, some behind firewalls. We need to remotely update the JAR files and start

Answer 1

I would use ansible to distribute jars to multiple servers and run update scripts.

For an update to be unnoticeable for users the application would have to stop the old instance and bring up a new one very quickly, in which java apps aren't very good.

There are ways to make update without any downtime, but none of them is free. Choosing a solution you should consider what downtime is acceptable to you and what cost can you accept to achieve it.

I see two options:

1. Rolling update, which means each time you update you spin up an instance with the new version, then validate if it is working correctly, and if it is, you kill the old version. This solution will require some kind of proxy (eg. haproxy) which will direct the traffic to the valid instances.
2. Optimizing application start-up time.

As Will Hartung mentioned you will also have to consider external dependencies like database schema which you might also want to update. In order to get seamless updates, you might also want to do a rolling update on a database. It would require you to do not introduce any breaking changes between any two consecutive releases of the application. Eg. when you want to delete a column, in the first release you remove all references to the column in an application and in next release you are allowed to delete the column in the database.