Is it possible to attach to a running background process with ruby?

Question

I have a nodejs daemon running on my server, I would like to give him some input on stdin and read it stdout from a Rails controller, is it possible with Ruby?

I am looking at Open3 but it seems to give me only the chance to spawn a new process.

I need the keep the nodejs process running because the starting overhead is too high to be called at every request.

You could set up the Node process to run a server and accept input on a given port. Then just make net requests from Ruby to Node — Jordan Kasper, Dec 20 '17 at 16:26
No doubt... just a thought if you get no other ways to do so (I'm not a Ruby person). You could actually go below HTTP though, make it a straight TCP request using the [Net API](https://nodejs.org/api/net.html) — Jordan Kasper, Dec 20 '17 at 17:28
If the request is so frequent that even local HTTP has significant overhead, try Unix domain socket. — Franklin Yu, Dec 20 '17 at 21:06

score 0 · Answer 1 · answered Dec 20 '17 at 21:30

In general there is no way to attach to a running process's IO streams unless it was set up to do so initially. It is easy if, for example, the process was set up to read from a pipe: just have Ruby write to that pipe like any other file (this is what the Open3 lib does).

For a daemon usually there are more proper ways to interact with it than hijacking its input with a pipe, though it depends on the particular daemon you are running and how it is being managed by the OS. For example, sockets are a popular way to communicate to a running process on *nix systems.

Is it possible to attach to a running background process with ruby?

1 Answers1