Persistance

What is Persistence?

In general, persistence refers to the ability or functionality that allows objects or system states to be maintained or saved across physical and temporal boundaries.

For instance, data stored in memory is easily lost when a program terminates or the computer is powered off. However, if this data is stored in a database using recording media such as hard disks, it remains intact even after the program ends or the computer shuts down, achieving persistence. In object-oriented programming languages like Java, saving the information held by objects into a database or similar storage is commonly referred to as persistence, and the APIs used for this process are known as Persistence APIs.

In the context of load balancers, persistence refers to the functionality of ensuring that multiple requests from the same client are consistently redirected to the same server to maintain web application sessions. This is one of the most critical functionalities a load balancer needs to implement, as persistence guarantees the continuity of transactions.

F5’s BIG-IP provides multiple methods to achieve persistence, including:

• Source Address Affinity Persistence: Determines the target server based on the source IP address.
• Cookie Persistence: Uses cookie information to assign requests to the appropriate server.
• SSL Persistence: Maintains persistence based on SSL session IDs.
• Layer 7 Client Identification: Tracks and assigns requests based on Layer 7 information.