- Learn AWS
- Architecture
- Cache-aside reads
Architecture pattern
AWS Cache-aside reads architecture
when reads vastly outnumber writes and the database feels it
The application asks the cache first and falls back to the database on a miss, writing the answer back as it goes. Most reads never reach the database, which is what lets a modest instance serve a large audience.
What it runs through
In the order a request or a record moves through it. Each one links to the page that explains it.
- ALBApplication Load Balancer
- ECS on FargateAmazon ECS on AWS Fargate
- ElastiCache RedisAmazon ElastiCache for Redis
- RDSAmazon RDS
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.
- “read heavy”
- “a hundred times more reads than writes”
- “the same data over and over”
- “database under load”
What it costs you
Two copies of the truth. Every write needs a story for how the cache stops being wrong.
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 ELBSpreads incoming traffic across healthy targets in several Availability Zones, with four kinds of load balancer: Application, Network, Gateway and Classic.
- AWS ElastiCacheA managed in-memory cache, Valkey, Redis OSS or Memcached, that answers repeated reads from memory so the database behind it does less.
- 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.