schema_version: 1
decision:
  id: queue-between-api-and-worker
  title: A queue between the API and the worker
  status: accepted
  date: 2026-09-16
  elements: [api, queue, worker]
  diagrams: [0200-containers/online-shop.archify]
context: >
  Order confirmation emails and invoices were sent inside
  the checkout request. A slow mail provider made checkout
  slow; a failing one made checkout fail.
decision: >
  The API enqueues a job per side effect on SQS. One worker
  service consumes the queue and does the slow work.
  Checkout returns as soon as the order is stored.
consequences: >
  Emails arrive seconds later, not instantly. Jobs must be
  idempotent because SQS delivers at least once. The worker
  is the second place that writes to the database.