Oban Activity Executor

Continuum can route activity execution through a host-operated Oban queue while keeping Continuum's durable workflow semantics unchanged.

Oban runs activities only. Workflow engines, replay, leases, timers, signals, idempotency, retry policy, and completion writes remain owned by Continuum.

When to Use It

Use the Oban executor when your application already operates Oban and wants activity attempts visible in Oban's queueing and operational tools.

Keep the built-in executor when you do not already need Oban. It has fewer moving parts and remains the default.

Setup

Add Oban to the host application's dependencies and run Oban's own migration:

{:oban, "~> 2.20"}

Start Oban in the host supervision tree with a queue for Continuum activities:

children = [
  MyApp.Repo,
  {Oban, repo: MyApp.Repo, queues: [continuum_activities: 10]},
  Continuum.children(
    name: :flows,
    repo: MyApp.Repo,
    activity_executor: {:oban, queue: :continuum_activities}
  )
]

For the default Continuum instance:

config :continuum,
  repo: MyApp.Repo,
  activity_executor: {:oban, queue: :continuum_activities}

Semantics

Continuum still inserts one row in continuum_activity_tasks when a workflow schedules an activity. The activity dispatcher enqueues an Oban job containing only the Continuum instance, task id, and task attempt.

The Oban worker claims the Continuum task row when the job performs. That claim captures the run's current fencing token immediately before the activity MFA runs. Completion then uses the same Journal.Postgres.complete_activity_task!/5, failure, retry, compensation, and idempotency paths as the built-in worker.

This means a job can sit in oban_jobs without holding a Continuum task lease. Duplicate or stale Oban jobs are harmless: only one job can claim a matching {task_id, attempt} and the rest no-op.

Oban retries are disabled for Continuum jobs. Continuum owns all activity retry and backoff through use Continuum.Activity.

Configuration

Supported executor options:

activity_executor:
  {:oban,
   queue: :continuum_activities,
   name: Oban,
   unique_period: 60,
   ttl_seconds: 30}

:queue selects the Oban queue. :name selects a non-default Oban supervision tree. :unique_period controls Oban duplicate-insert suppression for {instance, task_id, attempt}. :ttl_seconds controls the Continuum task lease once the Oban worker has claimed the task.

Oban uniqueness is operational hygiene, not correctness. Correctness comes from the perform-time Continuum task claim and completion CAS.