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Integrating Action Cable with Passenger

Relevant selection for this article:

Passenger + Nginx is fully compatible with Action Cable. You need at least Passenger version 5.0.24.

There are two ways to setup Action Cable with Passenger + Nginx:

Running the Action Cable server on the same host and port, under a sub-URI
Running the Action Cable server on a different host or port

Table of contents

Requirements

You need at least Passenger 5.0.24.
You need Redis, PostgreSQL, or any other inter-process adapter supported by Action Cable.

Preparation: edit 'config/cable.yml'

Passenger runs the Action Cable internally as a separate process. Action Cable defaults to the 'async' adapter, which does not work when multiple processes are involved. So you need to configure Action Cable to use a different adapter, such as Redis or PostgreSQL.

Here is an example that configures config/cable.yml to use Redis:

For example:

production:
  adapter: redis
  url: redis://redis.example.com:6379

local: &local
  adapter: redis
  url: redis://localhost:6379

development: *local
test: *local

Don't forget to start Redis.

Running the Action Cable server on the same host and port, under a sub-URI

This is the default setup as recommended by Rails and is also the easiest. It works by mounting ActionCable.server to a certain path in your config/routes.rb. That way, your Action Cable server will be running on the same host and port as your application, but under a sub-URI.

For example, your routes.rb may contain:

# Serve websocket cable requests in-process
mount ActionCable.server => '/cable'

(Although the routes.rb comment says that mounting ActionCable.server is meant for serving it in-process, Passenger actually insists on running it as a separate process.)

To make this work in Passenger + Nginx, you need to add a snippet to your Nginx virtual host. Suppose that you already had a virtual host for your application, which looks like this:

server {
    listen 80;
    server_name www.foo.com;
    root /path-to-your-app/public;
    passenger_enabled on;
}

You need to insert a location block which configures the Action Cable end point, like thisL

server {
    listen 80;
    server_name www.foo.com;
    root /path-to-your-app/public;
    passenger_enabled on;

    ### INSERT THIS!!! ###
    location /cable {
        passenger_app_group_name YOUR_APP_NAME_HERE_action_cable;
        passenger_force_max_concurrent_requests_per_process 0;
    }
}

Replace /cable with the actual Action Cable path as is specified in your routes.rb.
Replace YOUR_APP_NAME_HERE with a unique identifier that doesn't appear anywhere else in the Nginx configuration file.
The passenger_force_max_concurrent_requests_per_process option tunes Passenger for optimal WebSocket performance.

Running the Action Cable server on a different host or port

You can also run the Action Cable server on a different host and port. This approach allows you to scale out the Action Cable server separately from the normal Rails application processes.

Preparation: configure an Action Cable host and port

Before configuring Passenger, you need to decide on a hostname and port for your Action Cable server. Open config/environments/development.rb or config/environments/production.rb and specify your choice in the config.action_cable.url option.

Step 1: create a Rackup file

This setup requires a Rackup configuration file specifically for Action Cable. It is recommended that you call it cable/config.ru. A basic Rackup configuration for Action Cable looks as follows:

require ::File.expand_path('../../config/environment', __FILE__)
Rails.application.eager_load!

run ActionCable.server

Step 2: create a virtual host for your Action Cable server

Create a virtual host entry as follows:

server {
    listen YOUR_ACTION_CABLE_PORT_NUMBER_HERE;
    server_name YOUR_ACTION_CABLE_HOST_NAME_HERE;
    root /path-to-your-app/public;
    passenger_enabled on;
    passenger_app_group_name YOUR_APP_NAME_HERE_action_cable;
    passenger_app_type rack;
    passenger_startup_file cable/config.ru;
    passenger_force_max_concurrent_requests_per_process 0;
}

Replace YOUR_APP_NAME_HERE with a unique identifier that doesn't appear anywhere else in the Nginx configuration file.
The passenger_force_max_concurrent_requests_per_process option tunes Passenger for optimal WebSocket performance.

Restarting the Action Cable server

Main article: Restarting applications

If you want to restart the Action Cable server, then you must use the passenger-config restart-app command. Touching restart.txt does not work well, because restart.txt is checked at the beginning of every new request. But WebSockets are persistent, so restart.txt won't be checked often.