Clockwork - a clock process to replace cron
Cron is non-ideal for running scheduled application tasks, especially in an app deployed to multiple machines. More details.
Clockwork is a cron replacement. It runs as a lightweight, long-running Ruby process which sits alongside your web processes (Mongrel/Thin) and your worker processes (DJ/Resque/Minion/Stalker) to schedule recurring work at particular times or dates. For example, refreshing feeds on an hourly basis, or send reminder emails on a nightly basis, or generating invoices once a month on the 1st.
Quickstart
Create clock.rb:
require 'clockwork'
Run it with the clockwork executable:
$ clockwork clock.rb Starting clock for 4 events: [ frequent.job less.frequent.job hourly.job midnight.job ] Triggering frequent.job
If you need to load your entire environment for your jobs, simply add:
require './config/boot' require './config/environment'
under the
require 'clockwork' declaration.
Quickstart for Heroku
Clockwork fits well with heroku's cedar stack.
Consider to use clockwork-init.sh to create a new project for heroku.
Use with queueing
The clock process only makes sense as a place to schedule work to be done, not to do the work. It avoids locking by running as a single process, but this makes it impossible to parallelize. For doing the work, you should be using a job queueing system, such as Delayed Job, Beanstalk/Stalker, RabbitMQ/Minion, Resque, or Sidekiq. This design allows a simple clock process with no locks, but also offers near infinite horizontal scalability.
For example, if you're using Beanstalk/Stalker:
require 'stalker' module Clockwork handler { |job| Stalker.enqueue(job) } every(1.hour, 'feeds.refresh') every(1.day, 'reminders.send', :at => '01:30') end
Using a queueing system which doesn't require that your full application be loaded is preferable, because the clock process can keep a tiny memory footprint. If you're using DJ or Resque, however, you can go ahead and load your full application enviroment, and use per-event blocks to call DJ or Resque enqueue methods. For example, with DJ/Rails:
require 'config/boot' require 'config/environment' every(1.hour, 'feeds.refresh') { Feed.send_later(:refresh) } every(1.day, 'reminders.send', :at => '01:30') { Reminder.send_later(:send_reminders) }
Use with database events
In addition to managing static events in your
clock.rb, you can configure clockwork to synchronise with dynamic events from a database. Like static events, these database-backed events say when they should be run, and how frequently; the difference being that if you change those settings in the database, they will be reflected in clockwork.
To keep the database events in sync with clockwork, a special manager class
DatabaseEvents::Manager is used. You tell it to sync a database-backed model using the
sync_database_events method, and then, at the frequency you specify, it will fetch all the events from the database, and ensure clockwork is using the latest settings.
Example
clock.rb file
Here we're using an
ActiveRecord model called
ClockworkDatabaseEvent to store events in the database:
require 'clockwork' require 'clockwork/database_events' require_relative './config/boot' require_relative './config/environment' module Clockwork # required to enable database syncing support Clockwork.manager = DatabaseEvents::Manager.new sync_database_events model: ClockworkDatabaseEvent, every: 1.minute do |model_instance| # do some work e.g... # running a DelayedJob task, where #some_action is a method # you've defined on the model, which does the work you need model_instance.delay.some_action # performing some work with Sidekiq YourSidekiqWorkerClass.perform_async end [other events if you have] end
This tells clockwork to fetch all
ClockworkDatabaseEvent instances from the database, and create an internal clockwork event for each one. Each clockwork event will be configured based on the instance's
frequency and, optionally, its
at,
name,
if? and
tz methods. The code above also says to reload the events from the database every
1.minute; we need pick up any changes in the database frequently (choose a sensible reload frequency by changing the
every: option).
When one of the events is ready to be run (based on it's
frequency, and possible
at,
if? and
tz methods), clockwork arranges for the block passed to
sync_database_events to be run. The above example shows how you could use either DelayedJob or Sidekiq to kick off a worker job. This approach is good because the ideal is to use clockwork as a simple scheduler, and avoid making it carry out any long-running tasks.
Your Model Classes
ActiveRecord models are a perfect candidate for the model class. Having said that, the only requirements are:
the class responds to
allreturning an array of instances from the database
the instances returned respond to:
- `id` returning a unique identifier (this is needed to track changes to event settings) - `frequency` returning the how frequently (in seconds) the database event should be run - `attributes` returning a hash of [attribute name] => [attribute value] values (or really anything that we can use store on registering the event, and then compare again to see if the state has changed later) - (optionally) `at` return any acceptable clockwork `:at` string - (optionally) `name` returning the name for the event (used to identify it in the Clcockwork output) - (optionally) `if?` returning either true or false, depending on whether the database event should run at the given time (this method will be passed the time as a parameter, much like the standard clockwork `:if`) - (optionally) `tz` returning the timezone to use (default is the local timezone)
Example Setup
Here's an example of one way of setting up your ActiveRecord models:
# db/migrate/20140302220659_create_frequency_periods.rb class CreateFrequencyPeriods < ActiveRecord::Migration def change create_table :frequency_periods do |t| t.string :name t.timestamps end end end # 20140302221102_create_clockwork_database_events.rb class CreateClockworkDatabaseEvents < ActiveRecord::Migration def change create_table :clockwork_database_events do |t| t.integer :frequency_quantity t.references :frequency_period t.string :at t.timestamps end add_index :clockwork_database_events, :frequency_period_id end end # app/models/clockwork_database_event.rb class ClockworkDatabaseEvent < ActiveRecord::Base belongs_to :frequency_period attr_accessible :frequency_quantity, :frequency_period_id, :at # Used by clockwork to schedule how frequently this event should be run # Should be the intended number of seconds between executions def frequency frequency_quantity.send(frequency_period.name.pluralize) end end # app/models/frequency_period.rb class FrequencyPeriod < ActiveRecord::Base attr_accessible :name end # db/seeds.rb ... # creating the FrequencyPeriods [:second, :minute, :hour, :day, :week, :month].each do |period| FrequencyPeriod.create(name: period) end ...
Example use of
if?
Database events support the ability to run events if certain conditions are met. This can be used to only run events on a given day, week, or month, or really any criteria you could conceive. Best of all, these criteria e.g. which day to run it on can be attributes on your Model, and therefore change dynamically as you change the Model in the database.
So for example, if you had a Model that had a
day and
month integer attribute, you could specify that the Database event should only run on a particular day of a particular month as follows:
# app/models/clockwork_database_event.rb class ClockworkDatabaseEvent < ActiveRecord::Base ... def if?(time) time.day == day && time.month == month end ... end
Event Parameters
:at
:at parameter specifies when to trigger the event:
Valid formats:
HH:MM H:MM **:MM HH:** (Mon|mon|Monday|monday) HH:MM
Examples
The simplest example:
every(1.day, 'reminders.send', :at => '01:30')
You can omit the leading 0 of the hour:
every(1.day, 'reminders.send', :at => '1:30')
Wildcards for hour and minute are supported:
every(1.hour, 'reminders.send', :at => '**:30') every(10.seconds, 'frequent.job', :at => '9:**')
You can set more than one timing:
every(1.day, 'reminders.send', :at => ['12:00', '18:00']) # send reminders at noon and evening
You can specify the day of week to run:
every(1.week, 'myjob', :at => 'Monday 16:20')
If another task is already running at the specified time, clockwork will skip execution of the task with the
:at option.
If this is a problem, please use the
:thread option to prevent the long running task from blocking clockwork's scheduler.
:tz
:tz parameter lets you specify a timezone (default is the local timezone):
every(1.day, 'reminders.send', :at => '00:00', :tz => 'UTC') # Runs the job each day at midnight, UTC. # The value for :tz can be anything supported by [TZInfo]()
:if
:if parameter is invoked every time the task is ready to run, and run if the
return value is true.
Run on every first day of month.
Clockwork.every(1.day, 'myjob', :if => lambda { |t| t.day == 1 })
The argument is an instance of
ActiveSupport::TimeWithZone if the
:tz option is set. Otherwise, it's an instance of
Time.
This argument cannot be omitted. Please use _ as placeholder if not needed.
Clockwork.every(1.second, 'myjob', :if => lambda { |_| true })
:thread
By default, clockwork runs in a single-process and single-thread. If an event handler takes a long time, the main routine of clockwork is blocked until it ends. Clockwork does not misbehave, but the next event is blocked, and runs when the process is returned to the clockwork routine.
The
:thread option is to avoid blocking. An event with
thread: true runs in a different thread.
Clockwork.every(1.day, 'run.me.in.new.thread', :thread => true)
If a job is long-running or IO-intensive, this option helps keep the clock precise.
Configuration
Clockwork exposes a couple of configuration options:
:logger
By default Clockwork logs to
STDOUT. In case you prefer your
own logger implementation you have to specify the
logger configuration option. See example below.
:sleep_timeout
Clockwork wakes up once a second and performs its duties. To change the number of seconds Clockwork
sleeps, set the
sleep_timeout configuration option as shown below in the example.
From 1.1.0, Clockwork does not accept
sleep_timeout less than 1 seconds.
This restriction is introduced to solve more severe bug #135.
:tz
This is the default timezone to use for all events. When not specified this defaults to the local timezone. Specifying :tz in the parameters for an event overrides anything set here.
:max_threads
Clockwork runs handlers in threads. If it exceeds
max_threads, it will warn you (log an error) about missing
jobs.
:thread
Boolean true or false. Default is false. If set to true, every event will be run in its own thread. Can be overridden on a per event basis (see the
:thread option in the Event Parameters section above)
Configuration example
module Clockwork configure do |config| config[:sleep_timeout] = 5 config[:logger] = Logger.new(log_file_path) config[:tz] = 'EST' config[:max_threads] = 15 config[:thread] = true end end
error_handler
You can add error_handler to define your own logging or error rescue.
module Clockwork error_handler do |error| Airbrake.notify_or_ignore(error) end end
Current specifications are as follows.
- defining error_handler does not disable original logging
- errors from error_handler itself are not rescued, and stop clockwork
Any suggestion about these specifications is welcome.
Old style
include Clockwork is old style.
The old style is still supported, though not recommended, because it pollutes the global namespace.
Anatomy of a clock file
clock.rb is standard Ruby. Since we include the Clockwork module (the clockwork executable does this automatically, or you can do it explicitly), this exposes a small DSL to define the handler for events, and then the events themselves.
The handler typically looks like this:
handler { |job| enqueue_your_job(job) }
This block will be invoked every time an event is triggered, with the job name passed in. In most cases, you should be able to pass the job name directly through to your queueing system.
The second part of the file, which lists the events, roughly resembles a crontab:
every(5.minutes, 'thing.do') every(1.hour, 'otherthing.do')
In the first line of this example, an event will be triggered once every five minutes, passing the job name 'thing.do' into the handler. The handler shown above would thus call enqueue_your_job('thing.do').
You can also pass a custom block to the handler, for job queueing systems that rely on classes rather than job names (i.e. DJ and Resque). In this case, you need not define a general event handler, and instead provide one with each event:
every(5.minutes, 'thing.do') { Thing.send_later(:do) }
If you provide a custom handler for the block, the job name is used only for logging.
You can also use blocks to do more complex checks:
every(1.day, 'check.leap.year') do Stalker.enqueue('leap.year.party') if Date.leap?(Time.now.year) end
In addition, Clockwork also supports
:before_tick and
after_tick callbacks.
They are optional, and run every tick (a tick being whatever your
:sleep_timeout
is set to, default is 1 second):
on(:before_tick) do puts "tick" end on(:after_tick) do puts "tock" end
Finally, you can use tasks synchronised from a database as described in detail above:
sync_database_events model: MyEvent, every: 1.minute do |instance_job_name| # what to do with each instance end
You can use multiple
sync_database_events if you wish, so long as you use different model classes for each (ActiveRecord Single Table Inheritance could be a good idea if you're doing this).
In production
Only one clock process should ever be running across your whole application deployment. For example, if your app is running on three VPS machines (two app servers and one database), your app machines might have the following process topography:
- App server 1: 3 web (thin start), 3 workers (rake jobs:work), 1 clock (clockwork clock.rb)
- App server 2: 3 web (thin start), 3 workers (rake jobs:work)
You should use Monit, God, Upstart, or Inittab to keep your clock process running the same way you keep your web and workers running.
Daemonization
Thanks to @fddayan,
clockworkd executes clockwork script as a daemon.
You will need the daemons gem to use
clockworkd. It is not automatically installed, please install by yourself.
Then,
clockworkd -c YOUR_CLOCK.rb start
For more details, you can run
clockworkd -h.
Issues and Pull requests
If you find a bug, please create an issue - Issues · tomykaira/clockwork.
For a bug fix or a feature request, please send a pull-request. Do not forget to add tests to show how your feature works, or what bug is fixed. All existing tests and new tests must pass (TravisCI is watching).
We want to provide simple and customizable core, so superficial changes will not be merged (e.g. supporting new event registration style).
In most cases, directly operating
Manager realizes an idea, without touching the core.
If you discover a new way to use Clockwork, please create a gist page or an article on your website, then add it to the following "Use cases" section.
This tool is already used in various environment, so backward-incompatible requests will be mostly rejected.
Use cases
Feel free to add your idea or experience and send a pull-request.
Meta
Created by Adam Wiggins
Inspired by rufus-scheduler and resque-scheduler
Design assistance from Peter van Hardenberg and Matthew Soldo
Patches contributed by Mark McGranaghan and Lukáš Konarovský
Released under the MIT License: