Deploy Ruby on Rails app to Heroku while using Action Cable (listening on Puma port)

Problem

There are some restrictions for Heroku router : it will only listen on ports 80 and 443. In other words, you can Do not open a fixed port in any Heroku application. In the case of an ActionCable server, there is no way to open a fixed port and receive websocket traffic directed to it. So either Geroku allows things like this (which I doubt) or we use a workaround.

Bypass

As of version 0.0.3 actioncable this is the workaround I used.

The idea is to not have any Heroku app, but two: one for the main rails server and one for the ActionCable server. Both will work on port 80 (or 443).

To run two different servers from the same codebase, you just need to have two Procfiles: one for the rails and one for the action cable. There is a buildpack to handle this. To use it, you also need multi buildpack .

Let's say you have your two Heroku applications called rails

and actioncable

.

Create a file .buildpacks

at the root of your project with this:

https://github.com/cantino/heroku-selectable-procfile
https://github.com/heroku/heroku-buildpack-ruby

      

        
        
        
      

    

In rails

and actioncable

create env var BUILDPACK_URL

withhttps://github.com/heroku/heroku-buildpack-multi.git

Now for Procfiles, I want to leave Procfile

to run everything locally with a wizard and create two custom ones: Procfile.rails

and Procfile.actioncable

.

In Procfile.rails

you describe all the required dynos other than the action cable server, for example:

web: bundle exec puma -C config/puma/config.rb
clockwork: bundle exec clockwork lib/clockwork.rb
worker: bundle exec rake jobs:work

      

        
        
        
      

    

In Procfile.actioncable

you are describing the server only :

web: bundle exec puma -p $PORT cable/config.ru

      

        
        
        
      

    

Note that we are using a speaker web

that will mount the action cable server on port 80 (or 443).

CAUTION You need to move the puma config file config/puma.rb

to your custom location. I choose config/puma/config.rb

. config/puma.rb

is the default location when you start puma without any specific configuration file that we have in Procfile.actioncable

. This can lead to unexpected behavior (see comments below).

Now, on rails

, create env var PROCFILE_PATH

with Procfile.rails

and on actioncable

, create env var PROCFILE_PATH

with Procfile.actioncable

.

Speaking of env vars, it actioncable

needs all the env vars from rails

that needed to run the server actioncable like DATABASE_URL or any credentials.

Now the crucial step: how do we connect rails

and actioncable

together? This is simply done using a Redis instance of the same . rails

will send messages to Redis and actioncable

listen to them and act accordingly. This is why both should target the same Redis instance. If you are using Heroku Redis you just need to install REDIS_URL

with the same value on rails

and actioncable

. Here is the config file for the cable server cable.yml

:

production: &production
  :url: <%= ENV["REDIS_URL"] %>
  :timeout: 1
development: &development
  :url: <%= ENV["REDIS_URL"] %>
  :timeout: 1
  :inline: true
test: *development

      

        
        
        
      

    

The last step is to modify the javascript file so that we can control where the Action Action server is located. We can do this using env var.

Change the suffix .js

to, if necessary .js.erb

.

//= require cable
//= require_self
//= require_tree .


this.App = {};

App.cable = Cable.createConsumer('<%= ENV["CABLE_SERVER"] %>');

      

        
        
        
      

    

This variable CABLE_SERVER

can now point to ws://127.0.0.1:28080

locally and to rails

, the value will be the url actioncable

.

You are now ready to deploy the code to rails

and actioncable

.

Caveat / Disadvantages

• on actioncable
  
  , if you have client authentication you cannot use cookies
  
  as in examples . You now have two Heroku apps and they cannot share a cookie. I think you can still workaround using cookies for multiple subdomains.
• you have two deployment targets to support.
• You have several Procfiles to support.
• hopefully over time it will be easier to work around :)

Alternatives

• We can have the same server that handles regular web and websocket traffic using simple middleware. Here 's how.
• As of rails 5 beta2, the action cable server can now be side-mounted along with your main rail. Having two different servers can make sense: you can scale them individually.

HTH