Should I use forever/pm2 within a (Docker) container?

Question

I am refactoring a couple of node.js services. All of them used to start with forever on virtual servers, if the process crashed they just relaunch.

Now, moving to containerised and state-less application structures, I think the process should exit and the container should be restarted on a failure.

Is that correct? Are there benefits or disadvantages?

Answer 1

My take is do not use an in-container process supervisor (forever, pm2) and instead use docker restart policy via the --restart=always (or one of the other flavors of that option). This is more inline with the overall docker philosophy, and should operate very similarly to in-container process supervision since docker containers start running very quickly.

The strongest advocate for running in-container process supervision I've seen is in the phusion baseimage-docker README if you want to explore the other position on this topic.

Answer 2

While it's a good idea to use --restart=always as a failsafe, container restarting is relatively slow (5+ seconds with the simple Hello World Node server described here), so you can minimize app downtime using something like forever.

A downside of restarting the process within the container is that crash recovery can now happen two ways, which might have implications for your monitoring, etc.