For optimal performance among virtual machines, what should be ensured regarding the load balancer setup?

Session affinity settings, also known as "sticky sessions," allow client requests to consistently route to the same backend virtual machine for the duration of a user's session. This is particularly important for applications that maintain session state in memory on the server, which can enhance user experience by reducing latency and ensuring that users maintain continuity during their interactions with the application.

When session affinity is configured effectively, it optimizes the performance of virtual machines by reducing the overhead caused by establishing new sessions and re-establishing connections with different virtual machines. This is especially important for applications that require users to be continuously connected to the same VM, as it helps minimize disruptions in service and provides a seamless experience.

In contrast, while high availability configurations, advanced routing features, and multiple frontend IP addresses are all useful in creating robust and efficient load balancer setups, they primarily focus on redundancy, advanced networking configurations, and distribution of traffic rather than the specific nuances of user sessions that session affinity addresses.