Procfile

web: bundle exec rails server puma -p $PORT -e $RACK_ENV
critical: env HEROKU_PROCESS=critical bundle exec sidekiq -c 2 -q critical,4
default: env HEROKU_PROCESS=default bundle exec sidekiq -c 4 -q default,2
low: env HEROKU_PROCESS=low bundle exec sidekiq -c 1 -q low,1

sidekiq.rb

require 'sidekiq'
require 'autoscaler/sidekiq'
require 'autoscaler/heroku_scaler'

heroku = nil
if ENV['HEROKU_APP']
  heroku = {}
  scaleable = %w[critical default low] - (ENV['ALWAYS'] || '').split(' ')
  scaleable.each do |queue|
    heroku[queue] = Autoscaler::HerokuScaler.new(
      queue,
      ENV['HEROKU_API_KEY'],
      ENV['HEROKU_APP'])
  end
end

# When in Unicorn, this block needs to go in unicorn's `after_fork` callback:
# Configure the CLIENT
Sidekiq.configure_client do |config|
  config.redis = {url: ENV["REDISCLOUD_URL"], namespace: 'sidekiq'}

  if heroku
    config.client_middleware do |chain|
      p("Setting up auto-scaleer client middleware")
      chain.add Autoscaler::Sidekiq::Client, heroku
    end
  else
    p("Not scaleable client middleware")
  end
end


# Configure the SERVER
# define HEROKU_PROCESS in the Procfile:
#
#    default: env HEROKU_PROCESS=default bundle exec sidekiq -r ./background/boot.rb
#    import:  env HEROKU_PROCESS=import bundle exec sidekiq -q import -c 1 -r ./background/boot.rb
Sidekiq.configure_server do |config|
  config.redis = {url: ENV["REDISCLOUD_URL"], namespace: 'sidekiq'}

  # Heroku sets DATABASE_URL
  # For concurrency and High IO:
  # See: https://github.com/mperham/sidekiq/wiki/Advanced-Options
  database_url = ENV['DATABASE_URL']
  if (database_url)
    concurrency = Sidekiq.options[:concurrency].to_i
    # This will be the case on Heroku deployed environments
    uri = URI.parse(database_url)
    puts "Original DATABASE_URL => #{uri}"
    pool_size = (concurrency * 1.6).round(0)
    params = {}
    params['pool'] = pool_size
    uri.query = "#{params.to_query}"
    ENV['DATABASE_URL'] = uri.to_s
    puts "Sidekiq Server is reconnecting with new pool size: #{params['pool']} - DATABASE_URL => #{uri}"
    ActiveRecord::Base.establish_connection
  else
    # This will be the case in local environments (development & test)
    # Even trying to limit the concurrency results in too many connections.
    # So we just go with one per queue unless specified as ENV['SIDEKIQ_CONCURRENCY'].
    if ENV['SIDEKIQ_CONCURRENCY']
      Sidekiq.options[:concurrency] = ENV['SIDEKIQ_CONCURRENCY'].to_i
    else
      Sidekiq.options[:concurrency] = 1
    end
  end

  config.server_middleware do |chain|
    if heroku && ENV['HEROKU_PROCESS'] && heroku[ENV['HEROKU_PROCESS']]
      p("Setting up auto-scaleer server middleware")
      chain.add(Autoscaler::Sidekiq::Server, heroku[ENV['HEROKU_PROCESS']], 230, [ENV['HEROKU_PROCESS']])
    else
      p("Not scaleable server middleware")
    end
  end

  # Because our jobs running in the server can schedule other jubs, thus acting as clients,
  # we have to setup the client middleware in the server as well.
  # https://github.com/mperham/sidekiq/wiki/Middleware
  # https://github.com/mperham/sidekiq/issues/545
  # https://github.com/mperham/sidekiq/issues/175
  # https://github.com/JustinLove/autoscaler/issues/9#issuecomment-14069013
  config.client_middleware do |chain|
    if heroku && ENV['HEROKU_PROCESS'] && heroku[ENV['HEROKU_PROCESS']]
      p("Setting up auto-scaleer server-as-client middleware")
      chain.add Autoscaler::Sidekiq::Client, heroku
    else
      p("Not scaleable server-as-client middleware")
    end
  end
end