Embedding a falcon app (sinatra) in multithreaded ruby application

[pjmelling]

I'm building a ruby gem that does a bunch of things in separate threads, basically some IO stream processing. I want to embed a sinatra app using falcon in my application to provide an API for getting things like metrics and statistics from the stream processing part of the app. So the main entry point isn't falcon serve or the like. I'm running ruby my_app so that I can set up all the threads for the whole thing, including the web API thread. Basically, the web API isn't the main thing.

I also want to get a reference to the embedded web API server so that I can signal to it when it's time to shutdown for a graceful shutdown, or check on it's status, etc.

The only similar search result I've found for this type of thing is here, but it uses EventMachine and thin, neither of which I want to use. Also, all the examples I can find for using sinatra and/or falcon assume the web app is the main concern.

What's the best to accomplish this?

[ioquatix]

Falcon is the front end application server, it's not designed for embedding, but it's made up of components you can embed. You have two options:

• Use a service architecture, where falcon and the other parts of your application run side by side as processes.
• Use an internal server adjacent to your main program.

There are some limits to the latter, e.g. scaling up using multiple processes, etc. I'm going that isn't a problem for you.

As such, the simplest option is to run your entire program within Async and have a separate async task for your server, e.g.

require "async"
require "async/http/server"
require "async/http/endpoint"

protocol = Async::HTTP::Protocol::HTTP2
endpoint = Async::HTTP::Endpoint.parse("http://127.0.0.1:9222", reuse_port: true)

Async do
  server_task = Async do
    server = Async::HTTP::Server.for(endpoint, protocol: protocol) do |request|
      Protocol::HTTP::Response[200, {}, request.body]
    end
    server.run
  end
  
  # Main program.
end

You can stop the server by calling server_task.stop.

In order to host a Sinatra app, you will need to use protocol-rack to adapt it. There is an example of how to do this generically here: https://github.com/socketry/protocol-rack/blob/16197ef7bbf0be383e5a3b56f98068f925a9f313/examples/server/server.rb#L14

I assume for Sinatra it will be something like Protocol::Rack::Adapter.new(MySinatraApp.new). See https://github.com/sinatra/sinatra?tab=readme-ov-file#sinatrabase---middleware-libraries-and-modular-apps for documentation.