AWS Classic three-tier architecture

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.

• “existing application”
• “lift and shift”
• “high availability”
• “cannot be rewritten”
• “long-lived connections”

Learn the services in it

• AWS Route 53AWS's DNS service. It registers domains, answers queries for them with a choice of routing policies, and sends traffic away from endpoints that fail their health checks.
• AWS ELBSpreads incoming traffic across healthy targets in several Availability Zones, with four kinds of load balancer: Application, Network, Gateway and Classic.
• AWS Auto ScalingKeeps the right number of EC2 instances running. It replaces the ones that fail, and adds or removes instances as the load changes.
• 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.

• Cache-aside readsWhen reads vastly outnumber writes and the database feels it.
• Containerised servicesWhen a long-running service that is not a single function.
• Global multi-regionWhen users on several continents need the app to feel local.