Persistence

In certain situations, it may be desirable (for a time) for a client to reconnect repeatedly to the same real server, rather than have an LVS load balancing algorithm send that request to the best available server at that momement. Examples of such situations include multi-screen web forms, cookies, SSL, etc. In these cases, a client may not work properly unless the transactions are being handled by the same server in order to retain context. LVS provides a feature to handle this called persistence.

When enabled, persistence acts like a timer. When a client connects to a service, LVS remembers that last connection for a specified period of time. If that same client IP address connects again within that period, it will be sent to the same server that it used previously — bypassing the load balancing mechanisms. When a connecton occurs outside the time window, it is handled according to the scheduling rules in place.

Persistence also allows you to specify a subnet mask to apply to the client IP address test as a tool for controlling what addresses qualify.