Oban.Pro.Plugins.DynamicLifeline (Oban Pro v1.5.0-rc.7)

The DynamicLifeline plugin uses producer records to periodically rescues orphaned jobs, i.e. jobs that are stuck in the executing state because the node was shut down before the job could finish. In addition, it performs the following maintenance tasks:

  • Discard jobs left available with an attempt equal to max attempts
  • Rescue stuck workflows with deleted dependencies or missed scheduling events
  • Rescue stuck chains with deleted dependencies or missed scheduling events

Without DynamicLifeline you'll need to manually rescue stuck jobs or perform maintenance.

Using the Plugin

To use the DynamicLifeline plugin, add the module to your list of Oban plugins in config.exs:

config :my_app, Oban,
  plugins: [Oban.Pro.Plugins.DynamicLifeline]
  ...

There isn't any configuration necessary. By default, the plugin rescues orphaned jobs every 1 minute. If necessary, you can override the rescue interval:

plugins: [{Oban.Pro.Plugins.DynamicLifeline, rescue_interval: :timer.minutes(5)}]

If your system is under high load or produces a multitude of orphans you may wish to increase the query timeout beyond the 30s default:

plugins: [{Oban.Pro.Plugins.DynamicLifeline, timeout: :timer.minutes(1)}]

Note that rescuing orphans relies on producer records as used by the Smart engine.

Identifying Rescued Jobs

Rescued jobs can be identified by a rescued value in meta. Each rescue increments the rescued count by one.

Rescuing Exhausted Jobs

When a job's attempt matches its max_attempts its retries are considered "exhausted". Normally, the DynamicLifeline plugin transitions exhausted jobs to the discarded state and they won't be retried again. It does this for a couple of reasons:

  1. To ensure at-most-once semantics. Suppose a long-running job interacted with a non-idempotent service and was shut down while waiting for a reply; you may not want that job to retry.

  2. To prevent infinitely crashing BEAM nodes. Poorly behaving jobs may crash the node (through NIFs, memory exhaustion, etc.) We don't want to repeatedly rescue and rerun a job that repeatedly crashes the entire node.

Discarding exhausted jobs may not always be desired. Use the retry_exhausted option if you'd prefer to retry exhausted jobs when they are rescued, rather than discarding them:

plugins: [{Oban.Pro.Plugins.DynamicLifeline, retry_exhausted: true}]

During rescues, with retry_exhausted: true, a job's max_attempts is incremented and it is moved back to the available state.

Instrumenting with Telemetry

The DynamicLifeline plugin adds the following metadata to the [:oban, :plugin, :stop] event:

  • :rescued_jobs — a list of jobs transitioned back to available

  • :discarded_jobs — a list of jobs transitioned to discarded

Note: jobs only include id, queue, and state fields.

Summary

Types

option()

Types

Link to this type

option()

@type option() ::
  {:conf, Oban.Config.t()}
  | {:name, Oban.name()}
  | {:retry_exhausted, boolean()}
  | {:rescue_interval, timeout()}
  | {:timeout, timeout()}