Cluster Architecture

The best clustering configuration will depend on your traffic needs, existing infrastructure, and budget. One possible clustering configuration is pictured below:

There are three layers to this setup:

• Load-balancer Between users and the application servers is a load-balancing device. The device may be hardware-based or software-based. Every user has a session (represented by a unique cookie value) that allows stateful data to be maintained while they are using the application. Each session is created on a particular application server. The load-balancer must be "session-aware," meaning that it inspects the cookie value and always sends a given user's requests to the same application server during a given session. Without session-aware load balancing, the load-balancer could send requests to any application server in the cluster, scrambling results for a given user.
• Application Servers In the middle-tier, multiple application servers are set up and the clustering feature is enabled. Caches between the application instances are automatically synchronized. If a particular application server fails, the load-balancer detects this and removes the server from the cluster.
• Database All instances in a cluster must share the same database.