resque_instrumentation

Plugin to that adds instrumentation notifications to Resque's existing hooks.

Depends on Resque ~> 1.24

Purpose

Gain visibility into Resque's operation by instrumenting major Resque lifecycle events.

Installation

Install the gem directly:

$ gem install resque_instrumentation

Or add it to your Gemfile

gem 'resque_instrumentation', git: "[email protected]:rwdaigle/resque_instrumentation.git"

Worker level instrumentation is automatically enabled. To add instrumentation to your jobs (which is where the bulk of the hooks are), simply extend the Instrumentation::Job module in your job class:

class MyJob
  extend Resque::Plugins::Instrumentation::Job  
  # ...
end

Instrumentors

By default, resque_instrumentation discards emitted events. To do anything interesting you will need to specify an instrumentor which receives events directly from Resque and operates on them. An instrumentor is anything that adheres to the ActiveSupport::Notifications API by responding to instrument(name, params = {}, &block).

ActiveSupport::Notifications

Resque::Plugins::Instrumentation.instrumentor = ActiveSupport::Notifications
ActiveSupport::Notifications.subscribe(/^resque\.*/) do |name, start, finish, id, payload|
  # do what you want
end

Custom

A custom instrumentor would look something like this:

class LoggingInstrumentor

  def initialize(stream)
    @stream = stream
  end

  def instrument(name, params = {}, &block_given)
    stream.puts("event=#{name}.start #{params.inspect}")
    if(block_given?)
      result = yield
      stream.puts("event=#{name}.end")
      return result
    end
  end
end

Resque::Plugins::Instrumentation.instrumentor = LoggingInstrumentor.new(STDOUT)

Events

resque_instrumentation simply instruments each of Resque's existing hooks. The list of events instrumented is:

Target	Hook	Event name	Event params
Worker	before_first_fork	resque.before_first_fork	-
Worker	before_fork	resque.before_fork	-
Worker	after_fork	resque.after_fork	-
Job	before_enqueue	resque.before_enqueue	queue, job, args
Job	after_enqueue	resque.after_enqueue	queue, job, args
Job	before_dequeue	resque.before_dequeue	queue, job, args
Job	after_dequeue	resque.after_dequeue	queue, job, args
Job	before_perform	resque.before_perform	queue, job, args
Job	perform	resque.perform	queue, job, args
Job	after_perform	resque.after_perform	queue, job, args
Job	on_failure	resque.on_failure	exception, queue, job, args

Please see the Resque hook docs for additional details.

FAQs

Why not hooks?

Resque already has hooks in place that let you plug in to the before and after points of most major operations, couldn't I just add my desired instrumentation directly like this?

class MyJob
  def around_perform_with_instrumentation(*args)
    ActiveSupport::Notifications.instrument("resque.perform") { yield }
  end
end

Absolutely you can! However, this plugin provides the following benefits:

• Distribution: Once you have any architectural sophistication in your system, you will need a way to share common instrumentation logic, whether it be in a common Job superclass or something else. Being a Resque plugin, it solves the distribution issue, is easily shared amongst the various apps in your system, and encourages an idiomatic approach to instrumentation.
• Flexibility: The plugin is architected in a way that is instrumentation framework agnostic. Rest easy knowing you can switch out your current ActiveSupport::Notifications instrumentor with a custom implementation by changing a single line.