Introduction to Sun Cluster

Sun Cluster extends the Solaris^TM operating environment into a cluster operating system. A cluster is a collection of loosely coupled computing nodes that provides a single client view of network services or applications, including databases, web services, and file services.

Each cluster node is a standalone server that runs its own processes. These processes can communicate with one another to form what looks like (to a network client) a single system that cooperatively provides applications, system resources, and data to users.

A cluster offers several advantages over traditional single server systems. These advantages include support for highly available and scalable applications, capacity for modular growth, and low entry price compared to traditional hardware fault-tolerant systems.

The goals of Sun Cluster are:

• Reduce or eliminate system downtime because of software or hardware failure

• Ensure availability of data and applications to end users, regardless of the kind of failure that would normally take down a single server system

• Increase application throughput by enabling services to scale to additional processors by adding nodes to the cluster

• Provide enhanced availability of the system by enabling you to perform maintenance without shutting down the entire cluster

High Availability in Sun Cluster

Sun Cluster is designed as a highly available (HA) system, that is, a system that provides near continuous access to data and applications.

By contrast, fault-tolerant hardware systems provide constant access to data and applications, but at a higher cost because of specialized hardware. Additionally, fault-tolerant systems usually do not account for software failures.

Sun Cluster achieves high availability through a combination of hardware and software. Redundant cluster interconnects, storage, and public networks protect against single points of failure. The cluster software continuously monitors the health of member nodes and prevents failing nodes from participating in the cluster to protect against data corruption. Also, the cluster monitors applications and their dependent system resources, and fails over or restarts applications in case of failures.

Refer to "High Availability FAQ" for questions and answers on high availability.

Failover and Scalability in Sun Cluster

Sun Cluster enables you to implement applications on either a failover or scalable basis. Failover and scalable applications can also run on the same cluster concurrently. In general, a failover application provides high availability (redundancy), whereas a scalable application provides high availability along with increased performance. A single cluster can support both failover and scalable applications.

Failover

Failover is the process by which the cluster automatically relocates an application from a failed primary node to a designated secondary node. With failover, Sun Cluster provides high availability.

When a failover occurs, clients might see a brief interruption in service and might need to reconnect after the failover has finished. However, clients are not aware of the physical server from which they are provided the application and data.

Scalability

While failover is concerned with redundancy, scalability provides constant response time or throughput without regard to load. A scalable application leverages the multiple nodes in a cluster to concurrently run an application, thus providing increased performance. In a scalable configuration, each node in the cluster can provide data and process client requests.

Refer to "Data Services" for more specific information on failover and scalable services.