How to enable mongodb & redis when running a script on ubuntu using PM2?

Question

I ran the node.js express application on a drop of ubuntu digital drops. I use PM2 to run and monitor my application. I want to make sure - if the server needs to restart / crash, PM2 turns on my Redis and Mongo services when the server restarts, because they are necessary for my application. I think this is a fairly simple generic need, but could not find a direct answer. I would appreciate any help. cheers azhar