Robust job processing in Elixir, backed by modern PostgreSQL.
Reliable,
observable and loaded with enterprise grade 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 β 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 β Enqueue a job along with other database changes, ensuring that everything is committed or rolled back atomically.
- Database Backups β 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 β 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 β Queues can be paused, resumed and scaled independently at runtime.
- Resilient Queues β 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 β 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 β Database triggers ensure that jobs are dispatched as soon as they are inserted into the database.
- Unique Jobs β Duplicate work can be avoided through unique job controls. Uniqueness can be enforced at the argument, queue and worker level for any period of time.
- Scheduled Jobs β Jobs can be scheduled at any time in the future, down to the second.
- Job Safety β When a process crashes or the BEAM is terminated executing jobs aren't lostβthey are quickly recovered by other running nodes or immediately when the node is restarted.
- Historic Metrics β 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 β Every queue broadcasts metrics during runtime. These are used to monitor queue health across nodes.
- Queue Draining β Queue shutdown is delayed so that slow jobs can finish executing before shutdown.
- Telemetry Integration β Job life-cycle events are emitted via Telemetry integration. This enables simple logging, error reporting and health checkups without plug-ins.
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+.
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!
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.
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.
# config/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 want 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.
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.
Worker modules do the work of processing a job. At a minimum they must define a
perform/2
function, which is called with an args
map and the job struct.
Define a worker to process jobs in the events
queue:
defmodule MyApp.Business do
use Oban.Worker, queue: "events", max_attempts: 10
@impl Oban.Worker
def perform(%{"id" => id}, _job) do
model = MyApp.Repo.get(MyApp.Business.Man, id)
IO.inspect(model)
end
end
The value returned from perform/2
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).
The Business
worker can also be configured to prevent duplicates for a period
of time through the :unique
option. Here we'll configure it to be unique for
60 seconds:
use Oban.Worker, queue: "events", max_attempts: 10, unique: [period: 60]
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.Business.new()
|> Oban.insert()
The worker's defaults may be overridden by passing options:
%{vote_for: "none of the above"}
|> MyApp.Business.new(queue: "special", max_attempts: 5)
|> Oban.insert()
Jobs may be scheduled at a specific datetime in the future:
%{id: 1}
|> MyApp.Business.new(scheduled_at: ~U[2020-12-25 19:00:56.0Z])
|> Oban.insert()
Jobs may also be scheduled down to the second any time in the future:
%{id: 1}
|> MyApp.Business.new(schedule_in: 5)
|> Oban.insert()
Unique jobs can be configured in the worker, or when the job is built:
%{email: "[email protected]"}
|> MyApp.Mailer.new(unique: [period: 300, fields: [:queue, :worker])
|> Oban.insert()
Multiple jobs can be inserted in a single transaction:
Ecto.Multi.new()
|> Oban.insert(:b_job, MyApp.Business.new(%{id: 1}))
|> Oban.insert(:m_job, MyApp.Mailer.new(%{email: "[email protected]"}))
|> Repo.transaction()
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)
|> Oban.insert()
Oban.insert/2,4
is the preferred way of inserting jobs as it provides some of
Oban's advanced features (i.e., unique jobs). However, you can use your
application's Repo.insert/2
function if necessary.
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.
As noted in the Usage section above there are some guidelines for running tests:
-
Disable all job dispatching by setting
queues: false
orqueues: nil
in yourtest.exs
config. Keyword configuration is deep merged, so settingqueues: []
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 raiseDBConnection.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.
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: "[email protected]"})
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.
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.
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
)