N-tier architecture
N-tier architecture distributes an application across N physical tiers — typically presentation (browser or client), application server (business logic), and database. Each tier runs on separate hardware and communicates over the network. The pattern is the foundation of traditional enterprise web applications and remains common in regulated environments.
The most familiar version is 3-tier (browser + app server + database); larger systems may have 4-tier (add a caching tier or message broker) or 5+ tier (microservices, gateways, queues). The benefit is independent scaling of each tier (more app servers without more databases); the cost is network latency at every tier boundary. Modern serverless and edge architectures blur the tier boundaries — an edge function may serve both presentation and parts of the application tier. The pattern's vocabulary persists even where the deployment model has changed.
Related terms
- Layered architecture
Layered architecture organises an application into horizontal layers — typically presentation, business logic, data access — with each layer depending only on the layer below.
- Service-oriented architecture (SOA)
Service-oriented architecture is the design approach that structures applications as a collection of services communicating over a network — distinct from monoliths (single application) and microservices (small, independently deployable services).
- Microservices
Microservices is an architectural style where a single application is composed of many small, independently-deployable services, each owning its own data and communicating over the network.