Exq

Exq is a job processing library compatible with Resque / Sidekiq for the Elixir language.

• Exq uses Redis as a store for background processing jobs.
• Exq handles concurrency, job persistence, job retries, reliable queueing and tracking so you don’t have to.
• Jobs are persistent so they would survive across node restarts.
• You can use multiple Erlang nodes to process from the same pool of jobs.
• Exq uses a format that is Resque/Sidekiq compatible.
  • This means you can use it to integrate with existing Rails / Django projects that also use a background job that’s Resque compatible - typically with little or no changes needed to your existing apps. However, you can also use Exq standalone.
  • You can also use the Sidekiq UI to view job statuses, as Exq is compatible with the Sidekiq stats format.
  • If you don’t need Resque/Sidekiq compatibility, another option to check out would be toniq which uses erlang serialization instead of JSON.
  • You can run both Exq and Toniq in the same app for different workers.
• Exq supports uncapped amount of jobs running, or also allows a max limit per queue.
• Exq supports job retries with exponential backoff.
• Exq tracks several stats including failed busy, and processed jobs.
• Exq stores in progress jobs in a backup queue (using the Redis RPOPLPUSH command). This means that if the system or worker is restarted while a job is in progress, the job will be re_enqueued when the node is restarted and not lost.
• Exq provides an optional web UI that you can use to view several stats as well as rate of job processing.

Getting Started:

This assumes you have an instance of Redis to use.

Installation:

Add exq to your mix.exs deps (replace version with the latest hex.pm package version):

  defp deps do
    [
      # ... other deps
      {:exq, "~> 0.6.3"}
    ]
  end

Then run mix deps.get.

Configuration:

By default, Exq will use configuration from your config.exs file. You can use this to configure your Redis host, port, password, as well as namespace (which helps isolate the data in Redis). The name you can custom Exq’s name by anything, same as Exq.start_link([name: Name]) default is Exq The queues list specifices which queues Exq will listen to for new jobs. The concurrency setting will let you configure the amount of concurrent workers that will be allowed, or :infinite to disable any throttling.

config :exq,
  name: Exq,
  host: "127.0.0.1",
  port: 6379,
  password: "optional_redis_auth",
  namespace: "exq",
  concurrency: :infinite,
  queues: ["default"],
  poll_timeout: 50,
  scheduler_poll_timeout: 200,
  scheduler_enable: true,
  max_retries: 25

Concurrency:

Exq supports concurrency setting per queue. You can specify the same concurrency option to apply to each queue or specify it based on a per queue basis.

Concurrency for each queue will be set at 1000:

config :exq,
  host: "127.0.0.1",
  port: 6379,
  namespace: "exq",
  concurrency: 1000,
  queues: ["default"]

Concurrency for q1 is set at 10_000 while q2 is set at 10:

config :exq,
  host: "127.0.0.1",
  port: 6379,
  namespace: "exq",
  queues: [{"q1", 10_000}, {"q2", 10}]

Job Retries:

Exq will automatically retry failed job. It will use an exponential backoff timing similar to Sidekiq or delayed_job to retry failed jobs. It can be configured via these settings:

config :exq,
  host: "127.0.0.1",
  port: 6379,
  ...
  scheduler_enable: true,
  max_retries: 25

Note that scheduler_enable has to be set to true and max_retries should be greater than 0.

OTP Application:

You can add Exq into your OTP application list, and it will start an instance of Exq along with your application startup. It will use the configuration from your config.exs file.

  def application do
    [
      applications: [:logger, :exq],
      #other stuff...
    ]
  end

When using Exq through OTP, it will register a process under the name Elixir.Exq - you can use this atom where expecting a process name in the Exq module.

Using iex:

If you’d like to try Exq out on the iex console, you can do this by typing iex -S mix after mix deps.get.

Standalone Exq:

You can run Exq standalone from the command line, to run it:

> mix exq.run

Workers

Enqueuing jobs:

To enqueue jobs:

{:ok, ack} = Exq.enqueue(Exq, "default", MyWorker, ["arg1", "arg2"])

{:ok, ack} = Exq.enqueue(Exq, "default", "MyWorker", ["arg1", "arg2"])

In this example, "arg1" will get passed as the first argument to the perform method in your worker, "arg2" will be second argument, etc.

You can also enqueue jobs without starting workers:

{:ok, sup} = Exq.Enqueuer.start_link([port: 6379])

{:ok, ack} = Exq.Enqueuer.enqueue(Exq.Enqueuer, "default", MyWorker, [])

You can also schedule jobs to start at a future time: You need to make sure scheduler_enable is set to true

Schedule a job to start in 5 mins

{:ok, ack} = Exq.enqueue_in(Exq, "default", 300, MyWorker, ["arg1", "arg2"])

Schedule a job to start at 8am 2015-12-25 UTC

time = Timex.Date.from({{2015, 12, 25}, {8, 0, 0}}) |> Timex.Date.to_timestamp
{:ok, ack} = Exq.enqueue_at(Exq, "default", time, MyWorker, ["arg1", "arg2"])

Dynamic queue subscriptions:

The list of queues that are being monitored by Exq is determined by the config.exs file or the parameters passed to Exq.start_link. However, we can also dynamically add and remove queue subscriptions after exq has started.

To subscribe to a new queue:

# last arg is optional and is the max concurrency for the queue
:ok = Exq.subscribe(Exq, "new_queue_name", 10)

To unsubscribe from a queue:

:ok = Exq.unsubscribe(Exq, "queue_to_unsubscribe")

Creating Workers:

To create a worker, create an elixir module matching the worker name that will be enqueued. To process a job with “MyWorker”, create a MyWorker module. Note that the perform also needs to match the number of arguments as well.

Here is an example of a worker:

defmodule MyWorker do
  def perform do
  end
end

We could enqueue a job to this worker:

{:ok, jid} = Exq.enqueue(Exq, "default", MyWorker, [])

The ‘perform’ method will be called with matching args. For example:

{:ok, jid} = Exq.enqueue(Exq, "default", "MyWorker", [arg1, arg2])

Would match:

defmodule MyWorker do
  def perform(arg1, arg2) do
  end
end

Using with Phoenix and Ecto

If you would like to use Exq alongside Phoenix and Ecto, you will need to add Exq to your supervision hierarchy so that the Ecto Repo is available by the time jobs start processing. To do this, edit your application file and add a supervisor module. For example, if we have an application called HelloPhoenix, you would edit lib/hello_phoenix.ex and add the Exq supervisor:

    children = [
      # Start the endpoint when the application starts
      supervisor(HelloPhoenix.Endpoint, []),
      # Start the Ecto repository
      worker(HelloPhoenix.Repo, []),

      #Add the Exq supervisor
      supervisor(Exq, [])

      # Here you could define other workers and supervisors as children
      # worker(HelloPhoenix.Worker, [arg1, arg2, arg3]),
    ]

Also, add :tzdata to your mix.exs application list:

  def application do
    [mod: {Chat, []},
     applications: [:phoenix, :phoenix_html, :cowboy, :logger, :tzdata]]
  end

Assuming you will be accessing the database from Exq workers, you will want to lower the concurrency level for those workers, as they are using a finite pool of connections and can potentially back up and time out. You can lower this through the concurrency setting, or perhaps use a different queue for database workers that have a lower concurrency just for that queue. Inside your worker, you would then be able to use the Repo to work with the database:

defmodule Worker do
  def perform do
    HelloPhoenix.Repo.insert!(%HelloPhoenix.User{name: "Hello", email: "world@yours.com"})
  end
end

Using alongside Sidekiq / Resque

To use alongside Sidekiq / Resque, make sure your namespaces as configured in exq match the namespaces you are using in Sidekiq. By default, exq will use the exq namespace, so you will have to change that.

Another option is to modify Sidekiq to use the Exq namespace in the sidekiq initializer in your ruby project:

Sidekiq.configure_server do |config|
  config.redis = { url: 'redis://127.0.0.1:6379', namespace: 'exq' }
end

Sidekiq.configure_client do |config|
  config.redis = { url: 'redis://127.0.0.1:6379', namespace: 'exq' }
end

For an implementation example, see sineed’s demo app illustrating Sidekiq to Exq communication.

If you would like to exclusively send some jobs from Sidekiq to Exq as your migration strategy, you should create queue(s) that are exclusively listened to only in Exq (and configure those in the queue section in the Exq config). Make sure they are not configured to be listened to in Sidekiq, otherwise Sidekiq will also take jobs off that queue. You can still Enqueue jobs to that queue in Sidekiq even though they are not being monitored:

Side::Client.push('queue' => 'elixir_queue', 'class' => 'ElixirWorker', 'args' => ['foo', 'bar'])

Security

By default, you Redis server could be open to the world. As by default, Redis comes with no password authentication, and some hosting companies leave that port accessible to the world.. This means that anyone can read data on the queue as well as pass data in to be run. Obviously this is not desired, please secure your Redis installation by following guides such as the Digital Ocean Redis Security Guide.

Web UI:

Exq has a separate repo, exq_ui which provides with a Web UI to monitor your workers:

See https://github.com/akira/exq_ui for more details.

Starting Exq manually:

Typically, Exq will start as part of the application along with the configuration you have set. However, you can also start Exq manually and set your own configuration per instance.

Here is an example of how to start Exq manually:

{:ok, sup} = Exq.start_link

To connect with custom configuration options (if you need multiple instances of Exq for example), you can pass in options under start_link:

{:ok, sup} = Exq.start_link([host: "127.0.0.1", port: 6379, namespace: "x"])

By default, Exq will register itself under the Elixir.Exq atom. You can change this by passing in a name parameter:

{:ok, exq} = Exq.start_link(name: Exq.Custom)

Questions? Issues?

For issues, please submit a Github issue with steps on how to reproduce the problem.

For questions, stop in at the #elixir-lang Slack group

Contributions

Contributions are welcome. Tests are encouraged.

To run tests / ensure your changes have not caused any regressions:

mix test --no-start

To run the full suite, including failure conditions (can have some false negatives):

mix test --trace --include failure_scenarios:true --no-start

Contributors:

Justin McNally (j-mcnally) (structtv)

Nick Sanders (nicksanders)

Nick Gal (nickgal)

zhongwencool (zhongwencool)

Ben Wilson (benwilson512)

Mike Lawlor (disbelief)

Udo Kramer (optikfluffel)

Andreas Franzén (triptec)

Daniel Perez (tuvistavie)

Victor Rodrigues (rodrigues)

Denis Tataurov (sineed)

David Le (dl103)

Roman Smirnov (romul)

akki91 (Akshay)

Rob Gilson (D1plo1d)

Benjamin Tan Wei Hao (benjamintanweihao)