oban

Features

Oban’s primary goals are reliability, consistency and observability.

Oban is a powerful and flexible library that can handle a wide range of background job use cases, and it is well-suited for systems of any size. It provides a simple and consistent API for scheduling and performing jobs, and it is built to be fault-tolerant and easy to monitor.

Oban 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 Other 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 a SQL database 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

• Isolated Queues — Jobs are stored in a single table but are executed in distinct queues. Each queue runs in isolation, ensuring that a job in a single slow queue can’t back up other faster queues.

• Queue Control — Queues can be started, stopped, paused, resumed and scaled independently at runtime locally or across all running nodes (even in environments like Heroku, without distributed Erlang).

• Resilient Queues — Failing queries won’t crash the entire supervision tree, instead a backoff mechanism will safely retry them again in the future.

• Job Canceling — Jobs can be canceled in the middle of execution regardless of which node they are running on. This stops the job at once and flags it as cancelled.

• Triggered Execution — Insert triggers ensure that jobs are dispatched on all connected nodes as soon as they are inserted into the database.

• Unique Jobs — Duplicate work can be avoided through unique job controls. Uniqueness can be enforced at the argument, queue, worker and even sub-argument level for any period of time.

• Scheduled Jobs — Jobs can be scheduled at any time in the future, down to the second.

• Periodic (CRON) Jobs — Automatically enqueue jobs on a cron-like schedule. Duplicate jobs are never enqueued, no matter how many nodes you’re running.

• Job Priority — Prioritize jobs within a queue to run ahead of others with ten levels of granularity.

• Historic Metrics — After a job is processed the row isn’t 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 records metrics to the database during runtime. These are used to monitor queue health across nodes and may be used for analytics.

• Graceful Shutdown — Queue shutdown is delayed so that slow jobs can finish executing before shutdown. When shutdown starts queues are paused and stop executing new jobs. Any jobs left running after the shutdown grace period may be rescued later.

• 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 requires Elixir 1.13+, Erlang 23+, and PostgreSQL 12.0+ or SQLite3 3.37.0+.

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:

config :my_app, Oban,
  queues: [default: 10, mailers: 20, events: 50, media: 5],
  repo: MyApp.Repo

You may also use an expanded form to configure queues with individual overrides:

queues: [
  default: 10,
  events: [limit: 50, paused: true]
]

The events queue will now start in a paused state, which means it won’t process anything until Oban.resume_queue/2 is called to start it.

There isn’t a limit to the number of queues or how many jobs may execute concurrently in each queue. Some additional guidelines:

Caveats & 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.

• Queue limits are local (per-node), not global (per-cluster). For example, running a queue with a local limit of one on three separate nodes is effectively a global limit of three. If you require a global limit you must restrict the number of nodes running a particular queue.

• 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.

Defining 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 %Oban.Job{} struct.

Note that the args field of the job struct will always have string keys, regardless of the key type when the job was enqueued. The args are stored as JSON and the serialization process automatically stringifies all keys. Also, because args are always encoded as JSON, you must ensure that all values are serializable, otherwise you’ll have encoding errors when inserting jobs.

Define a worker to process jobs in the events queue:

defmodule MyApp.Business do
  use Oban.Worker, queue: :events

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

    case args do
      %{"in_the" => "business"} ->
        IO.inspect(model)

      %{"vote_for" => vote} ->
        IO.inspect([vote, model])

      _ ->
        IO.inspect(model)
    end

    :ok
  end
end

The use macro also accepts options to customize max_attempts, priority, tags, unique, and replace options:

defmodule MyApp.LazyBusiness do
  use Oban.Worker,
    queue: :events,
    priority: 3,
    max_attempts: 3,
    tags: ["business"],
    unique: true,
    replace: [scheduled: [:scheduled_at]]

  @impl Oban.Worker
  def perform(_job) do
    # do business slowly

    :ok
  end
end

Like all use macros, options are defined at compile time. Avoid using Application.get_env/2 to define worker options. Instead, pass dynamic options at runtime by passing them to MyWorker.new/2:

MyApp.MyWorker.new(args, queue: dynamic_queue)

Successful jobs should return :ok or an {:ok, value} tuple. The value returned from perform/1 is used to control whether the job is treated as a success, a failure, cancelled or deferred for retrying later.

See the Oban.Worker docs for more details on failure conditions and Oban.Telemetry for details on job reporting.

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:

%{id: 1, in_the: "business", of_doing: "business"}
|> MyApp.Business.new()
|> Oban.insert()

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

%{id: 1, vote_for: "none of the above"}
|> MyApp.Business.new(queue: :special, max_attempts: 5)
|> Oban.insert()

Unique jobs can be configured in the worker, or when the job is built:

%{email: "brewster@example.com"}
|> MyApp.Mailer.new(unique: false)
|> Oban.insert()

Job priority can be specified using an integer from 0 to 9, with 0 being the default and highest priority:

%{id: 1}
|> MyApp.Backfiller.new(priority: 2)
|> Oban.insert()

Any number of tags can be added to a job dynamically, at the time it is inserted:

id = 1

%{id: id}
|> MyApp.OnboardMailer.new(tags: ["mailer", "record-#{id}"])
|> 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: "brewser@example.com"}))
|> 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.

See Oban.Job.new/2 for a full list of job options.

Scheduling Jobs

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

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

Jobs may also 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()

Scheduling is always in UTC. You’ll have to shift timestamps in other zones to UTC before scheduling:

%{id: 1}
|> MyApp.Business.new(scheduled_at: DateTime.shift_zone!(datetime, "Etc/UTC"))
|> Oban.insert()

Caveats & Guidelines

Usually, scheduled job management operates in global mode and notifies queues of available jobs via PubSub to minimize database load. However, when PubSub isn’t available, staging switches to a local mode where each queue polls independently.

Local mode is less efficient and will only happen if you’re running in an environment where neither Postgres nor PG notifications work. That situation should be rare and limited to the following conditions:

1. Running with a connection pooler, i.e., pg_bouncer, in transaction mode.
2. Running without clustering, i.e., without Distributed Erlang

If both of those criteria apply and PubSub notifications won’t work, then staging will switch to polling in local mode.

Prioritizing Jobs

Normally, all available jobs within a queue are executed in the order they were scheduled. You can override the normal behavior and prioritize or de-prioritize a job by assigning a numerical priority.

• Priorities from 0-9 are allowed, where 0 is the highest priority and 9 is the lowest.

• The default priority is 0, unless specified all jobs have an equally high priority.

• All jobs with a higher priority will execute before any jobs with a lower priority. Within a particular priority jobs are executed in their scheduled order.

Caveats & Guidelines

The default priority is defined in the jobs table. The least intrusive way to change it for all jobs is to change the column default:

alter table("oban_jobs") do
  modify :priority, :integer, default: 1, from: {:integer, default: 0}
end

Unique Jobs

The unique jobs feature lets you specify constraints to prevent enqueueing duplicate jobs. Uniqueness is based on a combination of job attribute based on the following options:

• :period — The number of seconds until a job is no longer considered duplicate. You should always specify a period, otherwise Oban will default to 60 seconds. :infinity can be used to indicate the job be considered a duplicate as long as jobs are retained.

• :fields — The fields to compare when evaluating uniqueness. The available fields are :args, :queue, :worker, and :meta. By default, fields is set to [:worker, :queue, :args].

• :keys — A specific subset of the :args or :meta to consider when comparing against historic jobs. This allows a job with multiple key/value pairs in the args to be compared using only a subset of them.

• :states — The job states that are checked for duplicates. The available states are :available, :scheduled, :executing, :retryable, :completed, :cancelled and :discarded. By default all states except for :discarded and :cancelled are checked, which prevents duplicates even if the previous job has been completed.

• :timestamp — Which timestamp to check the period against. The available timestamps are :inserted_at or :scheduled_at, and it defaults to :inserted_at for legacy reasons.

The simplest form of uniqueness will configure uniqueness for as long as a matching job exists in the database, regardless of state:

use Oban.Worker, unique: true

Configure the worker to be unique only for 60 seconds:

use Oban.Worker, unique: [period: 60]

Check the :scheduled_at timestamp instead of :inserted_at for uniqueness:

use Oban.Worker, unique: [period: 120, timestamp: :scheduled_at]

Only consider the :url key rather than the entire args:

use Oban.Worker, unique: [keys: [:url]]

Use Oban.Job.states/0 to specify uniqueness across all states, including cancelled and discarded:

use Oban.Worker, unique: [period: :infinity, states: Oban.Job.states()]

Detecting Unique Conflicts

When unique settings match an existing job, the return value of Oban.insert/2 is still {:ok, job}. However, you can detect a unique conflict by checking the jobs’ :conflict? field. If there was an existing job, the field is true; otherwise it is false.

You can use the :conflict? field to customize responses after insert:

case Oban.insert(changeset) do
  {:ok, %Job{id: nil, conflict?: true}} ->
    {:error, :failed_to_acquire_lock}

  {:ok, %Job{conflict?: true}} ->
    {:error, :job_already_exists}

  result ->
    result
end

Note that conflicts are only detected for jobs enqueued through Oban.insert/2,3. Jobs enqueued through Oban.insert_all/2 do not use per-job unique configuration.

Replacing Values

In addition to detecting unique conflicts, passing options to replace can update any job field when there is a conflict. Any of the following fields can be replaced per state: args, max_attempts, meta, priority, queue, scheduled_at, tags, worker.

For example, to change the priority and increase max_attempts when there is a conflict with a job in a scheduled state:

BusinessWorker.new(
  args,
  max_attempts: 5,
  priority: 0,
  replace: [scheduled: [:max_attempts, :priority]]
)

Another example is bumping the scheduled time on conflict. Either scheduled_at or schedule_in values will work, but the replace option is always scheduled_at.

UrgentWorker.new(args, schedule_in: 1, replace: [scheduled: [:scheduled_at]])

NOTE: If you use this feature to replace a field (e.g. args) in the executing state by doing something like: UniqueWorker.new(new_args, replace: [executing: [:args]]) Oban will update the args, but the job will continue executing with the original value.

Strong Guarantees

Unique jobs are guaranteed through transactional locks and database queries: they do not rely on unique constraints in the database. This makes uniqueness entirely configurable by application code, without the need for database migrations.

Testing

Find testing setup, helpers, and strategies in the testing guide.

Pruning Historic Jobs

Job stats and queue introspection are built on keeping job rows in the database after they have completed. This allows administrators to review completed jobs and build informative aggregates, at the expense of storage and an unbounded table size. To prevent the oban_jobs table from growing indefinitely, Oban provides active pruning of completed, cancelled and discarded jobs.

By default, the Pruner plugin retains jobs for 60 seconds. You can configure a longer retention period by providing a max_age in seconds to the Pruner plugin.

# Set the max_age for 5 minutes
config :my_app, Oban,
  plugins: [{Oban.Plugins.Pruner, max_age: 300}]
  ...

Caveats & Guidelines

• Pruning is best-effort and performed out-of-band. This means that all limits are soft; jobs beyond a specified age may not be pruned immediately after jobs complete.

• Pruning is only applied to jobs that are completed, cancelled or discarded. It’ll never delete a new job, a scheduled job or a job that failed and will be retried.

Periodic Jobs

Oban’s Cron plugin registers workers a cron-like schedule and enqueues jobs automatically. Periodic jobs are declared as a list of {cron, worker} or {cron, worker, options} tuples:

config :my_app, Oban,
  repo: MyApp.Repo,
  plugins: [
    {Oban.Plugins.Cron,
     crontab: [
       {"* * * * *", MyApp.MinuteWorker},
       {"0 * * * *", MyApp.HourlyWorker, args: %{custom: "arg"}},
       {"0 0 * * *", MyApp.DailyWorker, max_attempts: 1},
       {"0 12 * * MON", MyApp.MondayWorker, queue: :scheduled, tags: ["mondays"]},
       {"@daily", MyApp.AnotherDailyWorker}
     ]}
  ]

The crontab would insert jobs as follows:

• MyApp.MinuteWorker — Inserted once every minute
• MyApp.HourlyWorker — Inserted at the first minute of every hour with custom args
• MyApp.DailyWorker — Inserted at midnight every day with no retries
• MyApp.MondayWorker — Inserted at noon every Monday in the “scheduled” queue
• MyApp.AnotherDailyWorker — Inserted at midnight every day with no retries

The crontab format respects all standard rules and has one minute resolution. Jobs are considered unique for most of each minute, which prevents duplicate jobs with multiple nodes and across node restarts.

Like other jobs, recurring jobs will use the :queue specified by the worker module (or :default if one is not specified).

Caveats & Guidelines

• All schedules are evaluated as UTC unless a different timezone is provided. See Oban.Plugins.Cron for information about configuring a timezone.

• Workers can be used for regular and scheduled jobs so long as they accept different arguments.

• Duplicate jobs are prevented through transactional locks and unique constraints. Workers that are used for regular and scheduled jobs must not specify unique options less than 60s.

• Long running jobs may execute simultaneously if the scheduling interval is shorter than it takes to execute the job. You can prevent overlap by passing custom unique opts in the crontab config:

  custom_args = %{scheduled: true}

  unique_opts = [
    period: 60 * 60 * 24,
    states: [:available, :scheduled, :executing]
  ]

  config :my_app, Oban,
    repo: MyApp.Repo,
    plugins: [
      {Oban.Plugins.Cron,
       crontab: [
         {"* * * * *", MyApp.SlowWorker, args: custom_args, unique: unique_opts}
       ]}
    ]

Error Handling

When a job returns an error value, raises an error, or exits during execution the details are recorded within the errors array on the job. When the number of execution attempts is below the configured max_attempts limit, the job will automatically be retried in the future.

The retry delay has an exponential backoff, meaning the job’s second attempt will be after 16s, third after 31s, fourth after 1m 36s, etc.

See the Oban.Worker documentation on “Customizing Backoff” for alternative backoff strategies.

Error Details

Execution errors are stored as a formatted exception along with metadata about when the failure occurred and which attempt caused it. Each error is stored with the following keys:

• at The UTC timestamp when the error occurred at
• attempt The attempt number when the error occurred
• error A formatted error message and stacktrace

See the Instrumentation docs for an example of integrating with external error reporting systems.

Limiting Retries

By default, jobs are retried up to 20 times. The number of retries is controlled by the max_attempts value, which can be set at the Worker or Job level. For example, to instruct a worker to discard jobs after three failures:

use Oban.Worker, queue: :limited, max_attempts: 3

Limiting Execution Time

By default, individual jobs may execute indefinitely. If this is undesirable you may define a timeout in milliseconds with the timeout/1 callback on your worker module.

For example, to limit a worker’s execution time to 30 seconds:

def MyApp.Worker do
  use Oban.Worker

  @impl Oban.Worker
  def perform(_job) do
    something_that_may_take_a_long_time()

    :ok
  end

  @impl Oban.Worker
  def timeout(_job), do: :timer.seconds(30)
end

The timeout/1 function accepts an Oban.Job struct, so you can customize the timeout using any job attributes.

Define the timeout value through job args:

def timeout(%_{args: %{"timeout" => timeout}}), do: timeout

Define the timeout based on the number of attempts:

def timeout(%_{attempt: attempt}), do: attempt * :timer.seconds(5)

Instrumentation, Error Reporting, and Logging

Oban provides integration with Telemetry, a dispatching library for metrics. It is easy to report Oban metrics to any backend by attaching to :oban events.

Here is an example of a sample unstructured log handler:

defmodule MyApp.ObanLogger do
  require Logger

  def handle_event([:oban, :job, :start], measure, meta, _) do
    Logger.warning("[Oban] :started #{meta.worker} at #{measure.system_time}")
  end

  def handle_event([:oban, :job, event], measure, meta, _) do
    Logger.warning("[Oban] #{event} #{meta.worker} ran in #{measure.duration}")
  end
end

Attach the handler to success and failure events in application.ex:

events = [[:oban, :job, :start], [:oban, :job, :stop], [:oban, :job, :exception]]

:telemetry.attach_many("oban-logger", events, &MyApp.ObanLogger.handle_event/4, [])

The Oban.Telemetry module provides a robust structured logger that handles all of Oban’s telemetry events. As in the example above, attach it within your application.ex module:

:ok = Oban.Telemetry.attach_default_logger()

For more details on the default structured logger and information on event metadata see docs for the Oban.Telemetry module.

Instance and Database Isolation

You can run multiple Oban instances with different prefixes on the same system and have them entirely isolated, provided you give each supervisor a distinct id.

Here we configure our application to start three Oban supervisors using the “public”, “special” and “private” prefixes, respectively:

def start(_type, _args) do
  children = [
    Repo,
    Endpoint,
    {Oban, name: ObanA, repo: Repo},
    {Oban, name: ObanB, repo: Repo, prefix: "special"},
    {Oban, name: ObanC, repo: Repo, prefix: "private"}
  ]

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

Umbrella Apps

If you need to run Oban from an umbrella application where more than one of the child apps need to interact with Oban, you may need to set the :name for each child application that configures Oban.

For example, your umbrella contains two apps: MyAppA and MyAppB. MyAppA is responsible for inserting jobs, while only MyAppB actually runs any queues.

Configure Oban with a custom name for MyAppA:

config :my_app_a, Oban,
  name: MyAppA.Oban,
  repo: MyApp.Repo

Then configure Oban for MyAppB with a different name:

config :my_app_b, Oban,
  name: MyAppB.Oban,
  repo: MyApp.Repo,
  queues: [default: 10]

Now, use the configured name when calling functions like Oban.insert/2, Oban.insert_all/2, Oban.drain_queue/2, etc., to reference the correct Oban process for the current application.

Oban.insert(MyAppA.Oban, MyWorker.new(%{}))
Oban.insert_all(MyAppB.Oban, multi, :multiname, [MyWorker.new(%{})])
Oban.drain_queue(MyAppB.Oban, queue: :default)

Ecto Multi-tenancy

If you followed the Ecto guide on setting up multi-tenancy with foreign keys, you need to add an exception for queries originating from Oban. All of Oban’s queries have the custom option oban: true to help you identify them in prepare_query/3 or other instrumentation:

# Sample code, only relevant if you followed the Ecto guide on multi tenancy with foreign keys.
defmodule MyApp.Repo do
  use Ecto.Repo, otp_app: :my_app

  require Ecto.Query

  @impl true
  def prepare_query(_operation, query, opts) do
    cond do
      opts[:skip_org_id] || opts[:schema_migration] || opts[:oban] ->
        {query, opts}

      org_id = opts[:org_id] ->
        {Ecto.Query.where(query, org_id: ^org_id), opts}

      true ->
        raise "expected org_id or skip_org_id to be set"
    end
  end
end

Community

There are a few places to connect and communicate with other Oban users:

• Ask questions and discuss #oban on the Elixir Forum
• Request an invitation and join the #oban channel on Slack
• Learn about bug reports and upcoming features in the issue tracker
• Follow @sorentwo (Twitter)