Resque-scheduler is an extension to Resque that adds support for queueing items in the future.
Requires redis >=1.3.
Job scheduling is supported in two different way:
Recurring (or scheduled) jobs are logically no different than a standard cron job. They are jobs that run based on a fixed schedule which is set at startup.
The schedule is a list of Resque worker classes with arguments and a schedule frequency (in crontab syntax). The schedule is just a hash, but is most likely stored in a YAML like so:
queue_documents_for_indexing:
cron: "0 0 * * *"
class: QueueDocuments
args:
description: "This job queues all content for indexing in solr"
clear_leaderboards_contributors:
cron: "30 6 * * 1"
class: ClearLeaderboards
args: contributors
description: "This job resets the weekly leaderboard for contributions"
A queue option can also be specified. Then the job will go onto the specified queue if it is available (Even if @queue is specified in the job class). When the queue is given it is not necessary for the scheduler to load the class.
clear_leaderboards_moderator:
cron: "30 6 * * 1"
class: ClearLeaderboards
queue: scoring
args: moderators
description: "This job resets the weekly leaderboard for moderators"
And then set the schedule wherever you configure Resque, like so:
require 'resque_scheduler'
Resque.schedule = YAML.load_file(File.join(File.dirname(__FILE__), '../resque_schedule.yml'))
Keep in mind, scheduled jobs behave like crons: if your scheduler process (more on that later) is not running when a particular job is supposed to be queued, it will NOT be ran later when the scheduler process is started back up. In that sense, you can sort of think of the scheduler process as crond. Delayed jobs, however, are different.
A big shout out to rufus-scheduler for handling the heavy lifting of the actual scheduling engine.
Delayed jobs are one-off jobs that you want to be put into a queue at some point in the future. The classic example is sending email:
Resque.enqueue_at(5.days.from_now, SendFollowUpEmail, :user_id => current_user.id)
This will store the job for 5 days in the resque delayed queue at which time the scheduler process will pull it from the delayed queue and put it in the appropriate work queue for the given job and it will be processed as soon as a worker is available.
NOTE: The job does not fire exactly at the time supplied. Rather, once that time is in the past, the job moves from the delayed queue to the actual resque work queue and will be completed as workers as free to process it.
Also supported is Resque.enqueue_in which takes an amount of time in seconds
in which to queue the job.
The delayed queue is stored in redis and is persisted in the same way the standard resque jobs are persisted (redis writing to disk). Delayed jobs differ from scheduled jobs in that if your scheduler process is down or workers are down when a particular job is supposed to be queue, they will simply "catch up" once they are started again. Jobs are guaranteed to run (provided they make it into the delayed queue) after their given queue_at time has passed.
One other thing to note is that insertion into the delayed queue is O(log(n)) since the jobs are stored in a redis sorted set (zset). I can't imagine this being an issue for someone since redis is stupidly fast even at log(n), but full disclosure is always best.
Removing Delayed jobs
If you have the need to cancel a delayed job, you can do so thusly:
# after you've enqueued a job like:
Resque.enqueue_at(5.days.from_now, SendFollowUpEmail, :user_id => current_user.id)
# remove the job with exactly the same parameters:
Resque.remove_delayed(SendFollowUpEmail, :user_id => current_user.id)
If needed you can also have recurring jobs (scheduled) that are dynamically
defined and updated inside of your application. A good example is if you want
to allow users to configured when a report is automatically generated. This
can be completed by loading the schedule initially wherever you configure
Resque and setting Resque::Scheduler.dynamic to true. Then subsequently
updating the "schedules" key in redis, namespaced to the Resque namespace.
The "schedules" key is expected to be a redis hash data type, where the key
is the name of the schedule and the value is a JSON encoded hash of the
schedule configuration. There are methods on Resque to make this easy (see
below).
When the scheduler loops it will look for differences between the existing
schedule and the current schedule in redis. If there are differences it will
make the necessary changes to the running schedule. The schedule names that
need to be changed are stored in the schedules_changed set in redis.
To force the scheduler to reload the schedule you just send it the USR2
signal. This will force a complete schedule reload (unscheduling and
rescheduling everything).
To add/update, delete, and retrieve individual schedule items you should use the provided API methods:
Resque.set_schedule(name, config)Resque.get_schedule(name)Resque.remove_schedule(name)
For example:
Resque.set_schedule("create_fake_leaderboards", {
:cron => "30 6 * * 1",
:class => "CreateFakeLeaderboards",
:queue => scoring
})
In this way, it's possible to completely configure your scheduled jobs from inside your app if you so desire.
Some Resque extensions like resque-status use custom job classes with a slightly different API signature. Resque-scheduler isn't trying to support all existing and future custom job classes, instead it supports a schedule flag so you can extend your custom class and make it support scheduled job.
Let's pretend we have a JobWithStatus class called FakeLeaderboard
class FakeLeaderboard < Resque::JobWithStatus
def perform
# do something and keep track of the status
end
end
create_fake_leaderboards:
cron: "30 6 * * 1"
queue: scoring
custom_job_class: FakeLeaderboard
args:
rails_env: demo
description: "This job will auto-create leaderboards for our online demo and the status will update as the worker makes progress"
If your extension doesn't support scheduled job, you would need to extend the custom job class to support the #scheduled method:
module Resque
class JobWithStatus
# Wrapper API to forward a Resque::Job creation API call into
# a JobWithStatus call.
def self.scheduled(queue, klass, *args)
create(args)
end
end
end
Resque-Scheduler allows to create schedule jobs for specific envs. The arg
rails_env (optional) can be used to determine which envs are concerned by the
job:
create_fake_leaderboards:
cron: "30 6 * * 1"
class: CreateFakeLeaderboards
queue: scoring
args:
rails_env: demo
description: "This job will auto-create leaderboards for our online demo"
The scheduled job create_fake_leaderboards will be created only if the
environment variable RAILS_ENV is set to demo:
$ RAILS_ENV=demo rake resque:scheduler
NOTE: If you have added the 2 lines bellow to your Rails Rakefile (ie: lib/tasks/resque-scheduler.rake), the rails env is loaded automatically and you don't have to specify RAILS_ENV if the var is correctly set in environment.rb
Alternatively, you can use your resque initializer to avoid loading the entire rails stack.
$ rake resque:scheduler INITIALIZER_PATH=config/initializers/resque.rb
Multiple envs are allowed, separated by commas:
create_fake_leaderboards:
cron: "30 6 * * 1"
class: CreateFakeLeaderboards
queue: scoring
args:
rails_env: demo, staging, production
description: "This job will auto-create leaderboards"
NOTE: If you specify the rails_env arg without setting RAILS_ENV as an
environment variable, the job won't be loaded.
Resque-scheduler also adds to tabs to the resque-web UI. One is for viewing (and manually queueing) the schedule and one is for viewing pending jobs in the delayed queue.
The Schedule tab:
The Delayed tab:
Get get these to show up you need to pass a file to resque-web to tell it to
include the resque-scheduler plugin. You probably already have a file
somewhere where you configure resque. It probably looks something like this:
require 'resque' # include resque so we can configure it
Resque.redis = "redis_server:6379" # tell Resque where redis lives
Now, you want to add the following:
require 'resque_scheduler' # include the resque_scheduler (this makes the tabs show up)
As of resque-scheduler 2.0, it's no longer necessary to have the resque-web process aware of the schedule because it reads it from redis. But prior to 2.0, you'll want to make sure you load the schedule in this file as well. Something like this:
Resque.schedule = YAML.load_file(File.join(RAILS_ROOT, 'config/resque_schedule.yml')) # load the schedule
Now make sure you're passing that file to resque-web like so:
resque-web ~/yourapp/config/resque_config.rb
That should make the scheduler tabs show up in resque-web.
To install:
gem install resque-scheduler
The unless you specify the queue for each scheduled job, the scheduler
needs to know about your job classes (so it can put them into the appropriate
queue). To do so, extend the "resque:scheduler_setup" to load your app's code.
In rails, it would look something like this:
require 'resque_scheduler/tasks'
task "resque:scheduler_setup" => :environment # load the env so we know about the job classes
By default, "resque:scheduler_setup" invokes "resque:setup".
The scheduler process is just a rake task which is responsible for both queueing items from the schedule and polling the delayed queue for items ready to be pushed on to the work queues. For obvious reasons, this process never exits.
$ rake resque:scheduler
Supported environment variables are VERBOSE and MUTE. If either is set to
any nonempty value, they will take effect. VERBOSE simply dumps more output
to stdout. MUTE does the opposite and silences all output. MUTE supersedes
VERBOSE.
NOTE: You DO NOT want to run >1 instance of the scheduler. Doing so will result in the same job being queued more than once. You only need one instnace of the scheduler running per resque instance (regardless of number of machines).
This was intended to be an extension to resque and so resulted in a lot of the code looking very similar to resque, particularly in resque-web and the views. I wanted it to be similar enough that someone familiar with resque could easily work on resque-scheduler.
For bugs or suggestions, please just open an issue in github.