Async and serverless

The work that happens after the response: outbox, topics, queues, Lambda, tickets and email.

Part of the path: read these pages in order.

1. The transactional outbox

   How do a booking and its 'send the email' message never get out of step?

2. SNS fan-out

   Why publish one event to a topic instead of sending it to each worker?

3. SQS queues and the dead-letter queue

   What happens to a message that keeps failing?

4. The Lambda worker

   How does a message in a queue become a Lambda call, and what is a partial batch failure?

5. DynamoDB

   Why does the worker remember which jobs it already did, and why in DynamoDB?

6. S3 and presigned URLs

   How can a browser fetch or upload a file without having AWS credentials?

7. Email with SES

   How does the confirmation email get sent, and what happens when sending fails?