通过systemd套接字激活来启动Ruby on Rails应用程序（即，启动Rails服务器监听预先存在的套接字）

Question

As the title states, I'm trying to start a Ruby on Rails app through systemd socket activation. I've no prior experience with Ruby and the lack of quality documentation is frustrating.

Obtaining the listen socket from systemd is trivial enough, though I'm struggling to put that socket to use. Is there an app server, that accepts a pre-existing listen socket? Or do I have to write my own, possibly by implementing a Rack::Handler (going by what limited information I've been able to gather from the documentation)? In the latter case a minimal example implementation would be helpful.

I'm looking for a production-suitable, lightweight, least-effort solution, capable of serving an average of 2 concurrent users on embedded hardware.

Answer 1

Starting with Puma 3.0.0, socket activation is supported by its Rack module, which is used by rails server . This means that running bin/rails server puma from systemd with socket activation will now work out of the box (tested with Puma 3.9.1). One caveat is that you must start bin/rails inside your application root, not the globally installed version.

For more details on this setup and some examples, see my blogpost .

Answer 2

In absence of any alternatives, I'll likely end up using the Puma web server, which implements the systemd socket activation protocol .

EDIT: Puma does implement socket activation, but not in the Rack handler. I arrived at my initial conclusion via grep -r LISTEN_FDS and only discovered my mistake once I actually tried it.