For the purpose of this article, we'll be using the Ruby programming language to demonstrate how to integrate the Job Queue metric source into your application from scratch. This guide applies to any programming language, not just Ruby.

HireFire will periodically perform an HTTP GET request against an endpoint in your application. This'll happen at the following URL/PATH pattern:

http://your-domain.com/hirefire/<HIREFIRE_TOKEN>/info

The HIREFIRE_TOKEN  is an environment variable that you must set, and can be found in the HireFire UI when creating/updating a dyno manager.

Inside your application, you'll want to create a new route with the following path:

/hirefire/<HIREFIRE_TOKEN>/info

In Ruby on Rails, you would add something like this:

token = ENV["HIREFIRE_TOKEN"] || "development"
get "/hirefire/#{token}/info", to: "hirefire#info"

This will invoke the function info  inside the class HireFire . With this in place, you'll want to create a JSON response that contains your queue size(s) which HireFire will use to auto-scale your worker-type dynos.

The JSON format should be the following:

[{"name" : "worker", "quantity" : 32}]

So all that you have to do is query your particular worker library in any way you wish, and return an array of objects that contain the properties name -> stringand quantity -> int , where name  should reflect the dyno name in your Procfile  (e.g. worker ) and the quantity  should reflect the number of jobs in the queue that (in this case worker ) works on.

You can (and should) return multiple objects, one for each Procfile entry that you want HireFire to auto-scale, for example:

[{"name" : "worker", "quantity" : 32},
 {"name" : "urgent", "quantity" : 8}]

Going back to our Ruby on Rails example, here is what the (simplified) info  function would look like:

class HireFireController < ApplicationController
  # ... snip ...

  def info
    render json: JSON.generate([
      {name: "worker", quantity: count_worker},
      {name: "urgent_worker", quantity: count_urgent_worker}
    ])
  end

  private

  def count_worker
    # logic to count worker queue
  end

  def count_urgent_worker
    # logic to count urgent_worker queue
  end
end

Confirm that it works

With all this in place, start the local development server and access the following url:

http://localhost:3000/hirefire/development/info

You should now see a JSON response containing your queue sizes. If you do, congratulations, you're done! Deploy it to Heroku.

HireFire UI

Now that you've integrated HireFire into your application and deployed it to Heroku, log in to HireFire and create two managers named worker  and urgent_worker  and configure them based on your auto-scaling requirements. 

Don't forget to add the previously mentioned HIREFIRE_TOKEN  environment variable to your Heroku application.

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