Glossary
SQS (Simple Queue Service)
A managed queue. One part of your system drops messages in, another takes them out later.
Think of it as: A ticket rail in a restaurant kitchen. Waiters clip orders up, cooks take them down when ready.
What to know for Level 0
- A queue decouples sender and receiver: the sender drops a message and moves on. Bursts wait safely instead of overloading the database, and slow work happens in the background.
- Messages wait 4 days by default, up to 14, so a worker can be down for a while without anything being lost.
- A received message is hidden for the visibility timeout, not deleted. If the worker doesn't delete it in time, it reappears and is retried.
- Standard queues deliver at least once (occasionally twice) and not always in order, so workers must be idempotent. FIFO queues keep strict order and process each message exactly once.
- Sending and receiving are AWS API calls approved by IAM, for example
sqs:SendMessage on the queue's ARN.
More detail
Queues decouple systems: the sender doesn’t wait for, or even know about, the receiver. Messages wait for up to 14 days. When a consumer takes a message it becomes invisible for the visibility timeout; if it isn’t deleted in time, it reappears and gets retried. Standard queues are fast with at-least-once delivery. FIFO queues keep strict order and deliver exactly once.
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