- Learn AWS
- Architecture
- Queue-based load levelling
Architecture pattern
AWS Queue-based load levelling architecture
when the front takes more than the back can absorb
The classic answer to a spike hitting a system that cannot spike with it. Intake accepts and enqueues in milliseconds, so the customer gets an answer immediately; the worker drains at whatever rate the database can actually take. The queue is also the thing that stops an outage losing work.
What it runs through
In the order a request or a record moves through it. Each one links to the page that explains it.
Signals in a brief that point here
Phrases that, when you meet them in a scenario, mean this shape rather than another. They are the tell, and they are what an exam question is built around.
- “traffic spike”
- “must never reject an order”
- “downstream can only handle so much”
- “must survive an outage”
- “processed in order”
What it costs you
The answer to the customer becomes "accepted", not "done". Anything that must be confirmed synchronously cannot go behind the queue.
Every shape has one. A design decision with no stated downside is usually a decision nobody has finished making.
Learn the services in it
- AWS API GatewayA managed front door for APIs: REST, HTTP and WebSocket APIs that take each call, check who is calling, throttle it, and pass it to Lambda, another service or any HTTP backend.
- AWS LambdaRuns your code in response to events, with no servers to manage. You pay per request and by the millisecond, and a run lasts 15 minutes at most.
- AWS SQSA queue between the part of your system that creates work and the part that does it, so a slow or broken consumer never costs you the work.
- AWS RDS and AuroraManaged relational databases: six engines run for you, plus Aurora, AWS's own MySQL- and PostgreSQL-compatible engine, with standbys, replicas and backups built in.
Shapes it is easily confused with
These run through some of the same services, which is exactly why a brief that fits one can look like it fits another.
Now build it from a brief
Reading a shape and producing one from a scenario that never names a service are different skills, and the exam asks for the second. The scenarios give you the brief; you draw the architecture and it is scored against what the brief requires.