Multi-tier architecture

A simple three-tier architecture consists of a UI tier, an application or business tier, and a data tier.

These tiers are ordinarily implemented using web servers, application servers, and databases, respectively.

Cloud applications can be deployed at multiple locations. Typically, these locations are regions (that is, separate geographical areas) or zones (that is, distinct locations within a region connected by low latency networks).

This tiered architecture on the cloud supports auto scaling and load balancing of web servers and application servers. Further, it also implements a master-slave database model across two different zones or data centers (connected with high speed links). The master database is synchronously replicated to the slave. Overall, the architecture represents a simple way to achieve a highly scalable and highly available application in a cloud environment.

Let's take a look at the following diagram:

It is also possible to separate the tiers across two different regions, to provide for higher level of redundancy including data center wide or zone level failures. While designing high availability architectures across multiple regions, we need to address network traffic flow and data synchronization issues between the regions. Such issues are discussed in more detail in Chapter 5, Designing for and Implementing High Availability. The following diagram illustrates this architecture: