adamwiggins-minion

= Minion: super simple job queue over amqp

Minion makes processing jobs over AMQP simple and easy.

== Setup

Minion pulls the AMQP credentials out the environment via AMQP_URI.

$ export AMQP_URI="amqp://johndoe:abc123@localhost/my_vhost"

If no URI is supplied, Minion defaults to "amqp://guest:guest@localhost/" which is the default credentials for Rabbitmq running locally.

== Principles

Minion treats your jobs with respect. The queues are durable and not autodelete. When popping jobs off the queue, they will not receive an ack until the job is done. You can rest assured that once queued, the job will not be lost.

Sends are done synchronously and receives are done asynchronously. This allows you to Minion.enqueue() from the console, or in a mongrel and you don't need to worry about eventmachine. It also means that when enqueue returns, the AMQP server has received your message. Daemons set to receive messages however use eventmachine.

Message processing is done one at a time (prefetch 1). If you want tasks done in parallel, run two minions.

== Push a job onto the queue

Its easy to push a job onto the queue.

Minion.enqueue("make.sandwich", { "for" => "me", "with" => "bread" })

Minion expects a queue name (and will create it if needed). The second argument needs to be a hash.

== Processing a job

require 'minion'

include Minion

job "make.sandwich" do |args|
	Sandwich.make(args["for"],args["with"])
end

== Chaining multiple steps

If you have a task that requires more than one step just pass an array of queues when you enqueue.

Minion.enqueue([ "make.sandwich", "eat.sandwich" ], "for" => "me")

job "make.sandwich" do
	## this return value is merged with for => me and sent to the next queue
	{ "type" => "ham on rye" }  
end

job "eat.sandwich" do |args|
	puts "I have #{args["type"]} sandwich for #{args["me"]}"
end

== Error handling

When an error is thrown in a job handler, the job is requeued to be done later and the minion process exits. If you define an error handler, however, the error handler is run and the job is removed from the queue.

on_error do |e|
	puts "got an error! #{e}"
end

== Logging

Minion logs to stdout via "puts". You can specify a custom logger like this:

logger do |msg|
	puts msg
end