IBM® i high availability solutions can be used for load balancing. The most common technologies for workload balancing involve moving work to available resources. Contrast this with common performance management techniques that involve moving resources to work that does not achieve performance goals.
Example workload balancing technologies (each with its own HA implications) are:
- Front end routers
- These routers handle all incoming requests and then use an algorithm to distribute work more evenly across available servers. Algorithms may be as simple as sequential spreading (round robin) distribution or complex based on actual measured performance.
- Multiple application servers
- A user distributes work via some predefined configuration or policy across multiple application servers. Typically the association from requester to server is relatively static, but the requesters are distributed as evenly as possible across multiple servers.
- Distributed, multi-part application
- These applications work in response to end-user requests that actually flow across multiple servers. The way in which the work is distributed is transparent to the user. Each part of the application performs a predefined task and then passes the work on to the next server in sequence. The most common example of this type of workload balancing is a three-tiered application with a back-end database server.
- Controlled application switchover
- Work is initially distributed in some predetermined fashion across multiple servers. A server may host multiple applications, multiple instances of the same application, or both. If a given server becomes overloaded while other servers are running with excess capacity, the operations staff moves applications or instances of applications with associated data from the overloaded server to the under used server. Workload movement can be manual or automated based on a predetermined policy.