Optionally, remove master process or allow it to take requests

[nateberkopec]

The master process takes up a lot of memory in constrained environments, like Heroku or small VPSes. We could let the master process take requests. This "dirties" the master, but we could figure out a way to deal with that. For some people, an extra Puma process would be worth the tradeoff of any additional complications.

Thoughts:

• We'd have to shut down the threadpool before forking.
• Rails will take care of disconnecting itself from ActiveRecord I think.
• What other "dirty" state should we think about and try to clean up before fork?

[wjordan]

The master process takes up a lot of memory in constrained environments

Is this only an issue when preload_app is enabled and the master process loads the application code, or is the Puma code itself also taking up a lot of memory? If the preloaded app is the main issue, this could be fixed by the fork_worker option (#2099) which avoids preloading the app in the master process.

[nateberkopec]

Is this only an issue when preload_app is enabled and the master process loads the application code

Purely this case.

I don't remember - does #2099 still create a master?