oban: An Elixir repository from khedaywi

Robust job processing in Elixir, backed by modern PostgreSQL. Reliable,
observable and loaded with enterprise grade features.

Features
Requirements
Installation
Usage
Testing
Troubleshooting
Contributing

Features

Oban's primary goals are reliability, consistency and observability. It is fundamentally different from other background job processing tools because it retains job data for historic metrics and inspection. You can leave your application running indefinitely without worrying about jobs being lost or orphaned due to crashes.

Advantages over in-memory, mnesia, Redis and RabbitMQ based tools:

Fewer Dependencies — If you are running a web app there is a very good chance that you're running on top of a RDBMS. Running your job queue within PostgreSQL minimizes system dependencies and simplifies data backups.
Transactional Control — Enqueue a job along with other database changes, ensuring that everything is committed or rolled back atomically.
Database Backups — Jobs are stored inside of your primary database, which means they are backed up together with the data that they relate to.

Advanced features and advantages over other RDBMS based tools:

Isolated Queues — Jobs are stored in a single table but are executed in distinct queues. Each queue runs in isolation, ensuring that a jobs in a single slow queue can't back up other faster queues.
Queue Control — Queues can be paused, resumed and scaled independently at runtime.
Resilient Queues — Failing queries won't crash the entire supervision tree, instead they trip a circuit breaker and will be retried again in the future.
Job Killing — Jobs can be killed in the middle of execution regardless of which node they are running on. This stops the job at once and flags it as discarded.
Triggered execution — Database triggers ensure that jobs are dispatched as soon as they are inserted into the database.
Scheduled Jobs — Jobs can be scheduled at any time in the future, down to the second.
Job Safety — When a process crashes or the BEAM is terminated executing jobs aren't lost—they are quickly recovered by other running nodes or immediately when the node is restarted.
Historic Metrics — After a job is processed the row is not deleted. Instead, the job is retained in the database to provide metrics. This allows users to inspect historic jobs and to see aggregate data at the job, queue or argument level.
Node Metrics — Every queue broadcasts metrics during runtime. These are used to monitor queue health across nodes.
Queue Draining — Queue shutdown is delayed so that slow jobs can finish executing before shutdown.
Telemetry Integration — Job life-cycle events are emitted via Telemetry integration. This enables simple logging, error reporting and health checkups without plug-ins.

Requirements

Oban has been developed and actively tested with Elixir 1.8+, Erlang/OTP 21.1+ and PostgreSQL 11.0+. Running Oban currently requires Elixir 1.8+, Erlang 21+, and PostgreSQL 9.6+.

Installation

Oban is published on Hex. Add it to your list of dependencies in mix.exs:

def deps do
  [
    {:oban, "~> 0.5"}
  ]
end

Then run mix deps.get to install Oban and its dependencies, including Ecto, Jason and Postgrex.

After the packages are installed you must create a database migration to add the oban_jobs table to your database:

mix ecto.gen.migration add_oban_jobs_table

Open the generated migration in your editor and delegate the up and down functions to Oban.Migrations:

defmodule MyApp.Repo.Migrations.AddObanJobsTable do
  use Ecto.Migration

  defdelegate up, to: Oban.Migrations
  defdelegate down, to: Oban.Migrations
end

This will run all of Oban's versioned migrations for your database. Migrations between versions are idempotent and will never change after a release. As new versions are released you may need to run additional migrations.

Now, run the migration to create the table:

mix ecto.migrate

Next see Usage for how to integrate Oban into your application and start defining jobs!

Note About Releases

If you are using releases you may see Postgrex errors logged during your initial deploy (or any deploy requiring an Oban migration). The errors are only temporary. After the migration has completed each queue will start producing jobs normally.

Usage

Oban isn't an application and won't be started automatically. It is started by a supervisor that must be included in your application's supervision tree. All of your configuration is passed into the Oban supervisor, allowing you to configure Oban like the rest of your application.

# confg/config.exs
config :my_app, Oban,
  repo: MyApp.Repo,
  prune: {:maxlen, 100_000},
  queues: [default: 10, events: 50, media: 20]

# lib/my_app/application.ex
defmodule MyApp.Application do
  @moduledoc false

  use Application

  alias MyApp.{Endpoint, Repo}

  def start(_type, _args) do
    children = [
      Repo,
      Endpoint,
      {Oban, Application.get_env(:my_app, Oban)}
    ]

    Supervisor.start_link(children, strategy: :one_for_one, name: MyApp.Supervisor)
  end
end

If you are running tests (which you should be) you'll need to disable pruning and job dispatching altogether when testing:

# config/test.exs
config :my_app, Oban,
  queues: false,
  prune: :disabled

Without dispatch and pruning disabled Ecto will raise constant ownership errors and you won't be able to run tests.

Configuring Queues

Queues are specified as a keyword list where the key is the name of the queue and the value is the maximum number of concurrent jobs. The following configuration would start four queues with concurrency ranging from 5 to 50:

queues: [default: 10, mailers: 20, events: 50, media: 5]

There isn't a limit to the number of queues or how many jobs may execute concurrently. Here are a few caveats and guidelines:

Each queue will run as many jobs as possible concurrently, up to the configured limit. Make sure your system has enough resources (i.e. database connections) to handle the concurrent load.
Only jobs in the configured queues will execute. Jobs in any other queue will stay in the database untouched.
Be careful how many concurrent jobs make expensive system calls (i.e. FFMpeg, ImageMagick). The BEAM ensures that the system stays responsive under load, but those guarantees don't apply when using ports or shelling out commands.

Creating Workers

Worker modules do the work of processing a job. At a minimum they must define a perform/1 function, which is called with an args map.

Define a worker to process jobs in the events queue:

defmodule MyApp.Workers.Business do
  use Oban.Worker, queue: "events", max_attempts: 10

  @impl Oban.Worker
  def perform(%{"id" => id}) do
    model = MyApp.Repo.get(MyApp.Business.Man, id)

    IO.inspect(model)
  end
end

The value returned from perform/1 is ignored, unless it returns an {:error, reason} tuple. With an error return or when perform has an uncaught exception or throw then the error will be reported and the job will be retried (provided there are attempts remaining).

Enqueueing Jobs

Jobs are simply Ecto structs and are enqueued by inserting them into the database. For convenience and consistency all workers provide a new/2 function that converts an args map into a job changeset suitable for insertion:

%{in_the: "business", of_doing: "business"}
|> MyApp.Workers.Business.new()
|> MyApp.Repo.insert()

The worker's defaults may be overridden by passing options:

%{vote_for: "none of the above"}
|> MyApp.Workers.Business.new(queue: "special", max_attempts: 5)
|> MyApp.Repo.insert()

Jobs may also be scheduled down to the second any time in the future:

%{id: 1}
|> MyApp.Workers.Business.new(schedule_in: 5)
|> MyApp.Repo.insert()

Occasionally you may need to insert a job for a worker that exists in another application. In that case you can use Oban.Job.new/2 to build the changeset manually:

%{id: 1, user_id: 2}
|> Oban.Job.new(queue: :default, worker: OtherApp.Worker)
|> MyApp.Repo.insert()

Pruning

Although Oban keeps all jobs in the database for durability and observability, it's not a great thing if the table grows indefinitely. Job pruning helps us by deleting old records from the oban_jobs table. It has 3 modes:

Disabled - No jobs are deleted. Example: :disabled
Limit-based - Keeps the latest N records. Example: {:maxlen, 100_000}
Time-based - Keeps records for the last N seconds. Example for 7 days: {:maxage, 60 * 60 * 24 * 7}

Important: pruning is only applied to jobs that are completed or discarded (has reached the maximum number of retries or has been manually killed). It'll never delete a new job, a scheduled job or a job that failed and will be retried.

Testing

As noted in the Usage section above there are some guidelines for running tests:

Disable all job dispatching by setting queues: false or queues: nil in your test.exs config. Keyword configuration is deep merged, so setting queues: [] won't have any effect.
Disable pruning via prune: :disabled. Pruning isn't necessary in testing mode because jobs created within the sandbox are rolled back at the end of the test. Additionally, the periodic pruning queries will raise DBConnection.OwnershipError when the application boots.
Be sure to use the Ecto Sandbox for testing. Oban makes use of database pubsub events to dispatch jobs, but pubsub events never fire within a transaction. Since sandbox tests run within a transaction no events will fire and jobs won't be dispatched.
```
config :my_app, MyApp.Repo, pool: Ecto.Adapters.SQL.Sandbox
```

Oban provides some helpers to facilitate testing. The helpers handle the boilerplate of making assertions on which jobs are enqueued. To use the assert_enqueued/1 and refute_enqueued/1 helpers in your tests you must include them in your testing module and specify your app's Ecto repo:

use Oban.Testing, repo: MyApp.Repo

Now you can assert, refute or list jobs that have been enqueued within your tests:

assert_enqueued worker: MyWorker, args: %{id: 1}

# or

refute_enqueued queue: "special", args: %{id: 2}

# or

assert [%{args: %{"id" => 1}}] = all_enqueued worker: MyWorker

See the Oban.Testing module for more details.

Integration Testing

During integration testing it may be necessary to run jobs because they do work essential for the test to complete, i.e. sending an email, processing media, etc. You can execute all available jobs in a particular queue by calling Oban.drain_queue/1 directly from your tests.

For example, to process all pending jobs in the "mailer" queue while testing some business logic:

defmodule MyApp.BusinessTest do
  use MyApp.DataCase, async: true

  alias MyApp.{Business, Worker}

  test "we stay in the business of doing business" do
    :ok = Business.schedule_a_meeting(%{email: "monty@brewster.com"})

    assert %{success: 1, failure: 0} == Oban.drain_queue(:mailer)

    # Now, make an assertion about the email delivery
  end
end

See Oban.drain_queue/1 for additional details.

Troubleshooting

Heroku

If your app crashes on launch, be sure to confirm you are running the correct version of Elixir and Erlang (view requirements). If using the hashnuke/elixir buildpack, you can update the elixir_buildpack.config file in your application's root directory to something like:

# Elixir version
elixir_version=1.9.0

# Erlang version
erlang_version=22.0.3

Available Erlang versions are available here.

Contributing

To run the Oban test suite you must have PostgreSQL 10+ running locally with a database named oban_test. Follow these steps to create the database, create the database and run all migrations:

# Create the database
MIX_ENV=test mix ecto.create -r Oban.Test.Repo

# Run the base migration
MIX_ENV=test mix ecto.migrate -r Oban.Test.Repo

To ensure a commit passes CI you should run mix ci locally, which executes the following commands:

Check formatting (mix format --check-formatted)
Lint with Credo (mix credo --strict)
Run all tests (mix test --raise)
Run Dialyzer (mix dialyzer --halt-exit-status)

khedaywi/oban

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