Background jobs with Oban, part 1: stop blocking your LiveView

This post moves slow preview fetching out of a LiveView event handler and into an Oban job. It shows how the app keeps the link creation flow responsive by inserting a job after the link is saved, then letting a worker fetch the page, store the metadata, and mark the link ready or failed.

Reading notes

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• Oban stores jobs in the database, so if PostgreSQL is already in use there is no separate queue server to deploy.
• The example app, Unfurl, pastes in a URL, fetches page data, stores title, description, and preview image, and displays the result.
• The current implementation fetches preview data inside the LiveView save handler, so a slow site blocks the user.
• The setup adds oban and oban_web, runs mix deps.get, and creates an Oban jobs table with a migration based on Oban’s manual installation guide.
• The configuration uses Oban.Engines.Basic, points Oban at Unfurl.Repo, defines a previews queue with concurrency 5, sets pruner to delete finished jobs after seven days, and sets lifeline to rescue jobs after one hour.
• Oban is added to the application’s supervision tree, and test configuration sets testing: :manual so jobs are inserted but not executed automatically.
• A PreviewWorker module uses Oban.Worker with the previews queue and up to five attempts.
• The worker receives a job with a link ID, looks up the link, fetches preview data, applies it on success, and marks the link as failed on error.
• If the link no longer exists, the worker returns {:cancel, :link_deleted} so Oban stops retrying.
• The Links module gains fetch_link, apply_preview, mark_failed, and schedule_preview.
• apply_preview sets fetched_at to the current time and stores the fetched attributes with status ready.
• schedule_preview builds a job from the link ID with PreviewWorker.new and inserts it with Oban.insert.
• The LiveView save handler now creates the link, enqueues the job, and shows a flash message instead of fetching immediately.
• After the change, the page stays responsive, and the preview appears after refresh once the background work finishes.