Quantum

Cron-like job scheduler for Elixir.

---

• Setup
• Usage
  • Named jobs
  • Nodes
  • Timezone
  • Crontab format
  • Special expressions
  • Override default settings
  • GenServer timeout
  • Run Quantum as a global process
• Contribution
• License

---

Setup

To use Quantum in your project, edit the mix.exs file and add Quantum to both

1. the list of dependencies:

defp deps do
  [{:quantum, ">= 1.9.0"}]
end

2. and the list of applications:

def application do
  [applications: [:quantum]]
end

Usage

Configure your cronjobs in your config/config.exs like this:

config :quantum, :your_app,
  cron: [
    # Every minute
    "* * * * *":      {"Heartbeat", :send},
    # Every 15 minutes
    "*/15 * * * *":   fn -> System.cmd("rm", ["/tmp/tmp_"]) end,
    # Runs on 18, 20, 22, 0, 2, 4, 6:
    "0 18-6/2 * * *": fn -> :mnesia.backup('/var/backup/mnesia') end,
    # Runs every midnight:
    "@daily":         &Backup.backup/0
  ]

or like this:

config :quantum, :your_app,
  cron: [
    # Every minute
    "* * * * *": {MyApp.MyModule, :my_method}
  ]

or you can provide module as a string:

config :quantum, :your_app,
  cron: [
    # Every minute
    "* * * * *": {"MyApp.MyModule", :my_method}
  ]

Or even use cron-like format (useful with conform / exrm / edeliver):

config :quantum, :your_app,
  cron: [
    # Every minute
    "* * * * * MyApp.MyModule.my_method"
  ]

If you want to add jobs on runtime, this is possible too:

Quantum.add_job("1 * * * *", fn -> :ok end)

Named jobs

Job struct:

%Quantum.Job{
  name: :job_name, # is set automatically on adding a job
  schedule: "1 * * * *", # required
  task: {MyApp.MyModule, :my_method}, # required
  args: [:a, :b] # optional, default: []
  state: :active, # is used for internal purposes
  nodes: [:node@host], # default: [node()]
  overlap: false, # run even if previous job is still running?, default: true
  pid: nil, # PID of last executed task
  timezone: :utc # Timezone to run task in, defaults to Quantum default which is UTC
}

You can define named jobs in your config like this:

config :quantum, :your_app,
  cron: [
    news_letter: [
      schedule: "@weekly",
      task: "MyApp.NewsLetter.send", # {MyApp.NewsLetter, :send} is supported too
      args: [:whatever]
    ]
  ]

Possible options:

• schedule cron schedule, ex: "@weekly" / "1 * * * *" / ~e[1 * * * *] or %Crontab.CronExpression{minute: [1]}
• task function to be performed, ex: "MyApp.MyModule.my_method" or {MyApp.MyModule, :my_method}
• args arguments list to be passed to task
• nodes nodes list the task should be run on, default: [node()]
• overlap set to false to prevent next job from being executed if previous job is still running, default: true

It is possible to control the behavior of jobs at runtime. For runtime configuration, job names are not restricted to be atoms. Strings, atoms and charlists are allowed as job names.

Add a named job at runtime:

job = %Quantum.Job{schedule: "* * * * *", task: fn -> IO.puts "tick" end}
Quantum.add_job(:ticker, job)

Deactivate a job, i.e. it will not be performed until job is activated again:

Quantum.deactivate_job(:ticker)

Activate an inactive job:

Quantum.activate_job(:ticker)

Find a job:

Quantum.find_job(:ticker)
# %Quantum.Job{...}

Delete a job:

Quantum.delete_job(:ticker)
# %Quantum.Job{...}

Jobs with Second granularity

It is possible to specify jobs with second granularity. To do this the schedule parameter has to be provided with either a %Crontab.CronExpression{extended: true, ...} or with a set e flag on the e sigil. (The sigil must be imported from Crontab.CronExpression)

With Sigil:

import Crontab.CronExpression

config :quantum, :your_app,
  cron: [
    news_letter: [
      schedule: ~e[*/2]e, # Runs every two seconds
      task: "MyApp.NewsLetter.send", # {MyApp.NewsLetter, :send} is supported too
      args: [:whatever]
    ]
  ]

With Struct:

config :quantum, :your_app,
  cron: [
    news_letter: [
      schedule: %Crontab.CronExpression{extended: true, second: [5]}, # Runs every minute at second 5
      task: "MyApp.NewsLetter.send", # {MyApp.NewsLetter, :send} is supported too
      args: [:whatever]
    ]
  ]

The struct & sigil are documented here: https://hexdocs.pm/crontab/Crontab.CronExpression.html

Nodes

If you need to run a job on a certain node you can define:

config :quantum, :your_app,
  cron: [
    news_letter: [
      # your job config
      nodes: [:app1@myhost, "app2@myhost"]
    ]
  ]

NOTE If nodes is not defined current node is used and a job is performed on all nodes.

Timezone

Please note that Quantum uses UTC timezone and not local timezone by default.

To specify another timezone, add the following timezone option to your configuration:

config :quantum, :your_app,
  cron: [
    # Your cronjobs
  ]

config :quantum,
  timezone: "America/Chicago"

Valid options are :utc or a timezone name such as "America/Chicago". A full list of timezone names can be downloaded from https://www.iana.org/time-zones, or at https://en.wikipedia.org/wiki/List_of_tz_database_time_zones.

Timezones can also be configured on a per-job basis. This overrides the default Quantum timezone for a particular job. To set the timezone on a job, use the timezone key when creating the Quantum.Job structure.

%Quantum.Job{
  # ...
  timezone: "America/New_York"
}

Crontab format

Field	Allowed values
minute	0-59
hour	0-23
day of month	1-31
month	1-12 (or names)
day of week	0-6 (0 is Sunday, or use abbreviated names)

Names can also be used for the month and day of week fields. Use the first three letters of the particular day or month (case does not matter).

Special expressions

Instead of the first five fields, one of these special strings may be used:

String	Description
@annually	Run once a year, same as "0 0 1 1 *" or @yearly
@daily	Run once a day, same as "0 0 * * *" or @midnight
@hourly	Run once an hour, same as "0 * * * *"
@midnight	Run once a day, same as "0 0 * * *" or @daily
@monthly	Run once a month, same as "0 0 1 * *"
@reboot	Run once, at startup
@weekly	Run once a week, same as "0 0 * * 0"
@yearly	Run once a year, same as "0 0 1 1 *" or @annually

Override default settings

The default job settings can be configured as shown in the example below. So if you have a lot of jobs and do not want to override the default setting in every job, you can set them globally.

config :quantum,
  default_schedule: "* * * * *",
  default_args: ["my api key"],
  default_nodes: [:app1@myhost],
  default_overlap: false

config :quantum, :your_app,
  cron: [
    # Your cronjobs
  ]

GenServer timeout

Sometimes, you may come across GenServer timeout errors esp. when you have too many jobs or high load. The default GenServer.call timeout is 5000. You can override this default by specifying timeout setting in configuration.

config :quantum,
  timeout: 30_000

Or if you wish to wait indefinitely:

config :quantum,
  timeout: :infinity

Run Quantum as a global process

When you have a cluster of nodes, you may not want same jobs to be generated on every single node, e.g. jobs involving db changes.

In this case, you may choose to run Quantum as a global process, thus preventing same job being run multiple times because of it being generated on multiple nodes. With the following configuration, Quantum will be run as a globally unique process across the cluster.

config :quantum,
  global?: true

config :quantum, :your_app,
  cron: [
    # Your cronjobs
  ]

Contribution

This project uses the Collective Code Construction Contract (C4) for all code changes.

"Everyone, without distinction or discrimination, SHALL have an equal right to become a Contributor under the terms of this contract."

tl;dr

1. Check for open issues or open a new issue to start a discussion around a problem.
2. Issues SHALL be named as "Problem: description of the problem".
3. Fork the quantum-elixir repository on GitHub to start making your changes
4. If possible, write a test which shows that the problem was solved.
5. Send a pull request.
6. Pull requests SHALL be named as "Solution: description of your solution"
7. Your pull request is merged and you are added to the list of contributors

License

Apache License, Version 2.0