Ratio (Session) and Least Sessions

The Ratio (Session) load balancing method in an F5 LTM device refers to distributing the load based on the ratio of active sessions, where a session refers to a series of related message exchanges. The method works by associating a ratio value with each pool member, and the system then distributes user sessions based on those ratio values.

For example, if you have two servers, Server A with a ratio of 2 and Server B with a ratio of 1, for every three sessions, two will go to Server A, and one will go to Server B. Regarding the concept of a session in Ratio (Session), it is not necessarily tied to persistence like in Least Sessions. The term 'session' in this context generally refers to a series of related message exchanges that can occur over time, possibly over multiple TCP connections or IP datagrams. In other words, a session could be a single TCP connection or a series of requests and responses between a client and server within a certain time period.

When it comes to HTTP traffic, a session could indeed involve multiple messages over the same connection. A single HTTP session, for example, might consist of a client making multiple GET requests and receiving responses over the same TCP connection. As for why all requests were going to only one member when you applied this method, it could be due to a variety of reasons such as the configuration of ratio values, the nature of your traffic, or the health and availability of your pool members.