In computer architecture, a middle-tier cluster is a type of server cluster designed for use in multi-tier applications. In a three-tier application, for example, the middle tier typically consists of application servers and web servers. A middle-tier cluster is used to provide high availability and scalability for the application servers and web servers in the middle tier. In a typical deployment, the application servers in the middle tier are clustered together, and each server in the cluster is connected to a separate web server. The web servers are also clustered together, and each server in the web server cluster is connected to a separate database server. The database servers are not clustered together, but are instead configured for failover or replication. This type of deployment provides high availability and scalability for both the application servers and the web servers, while still providing reliable access to data in the event of a failure of one of the database servers.