Message Queues

Some operations do not need to finish before the user gets a response.

Examples include sending email, generating reports, processing videos and updating analytics.

Producer

User signs up
→ account created
→ welcome-email job queued
→ HTTP response returned

Consumer

Workers consume jobs and perform the actual work.

Retries

Attempt 1 → now
Attempt 2 → +10 seconds
Attempt 3 → +30 seconds
Attempt 4 → +2 minutes

Permanent failures should eventually move to a failed or dead-letter state.

At-Least-Once Delivery

if (await wasAlreadyProcessed(job.id)) {
  return;
}

await processJob(job);
await markProcessed(job.id);