Lightboard Lessons: BIG-IP Deployments in Azure Cloud

You will need to choose the correct affinity at the Azure LB side to maintain persistence when BIG-IP is active-active. Affinity is a separate LB setting from DSR floating IP. As for round-robin, Azure LB by default uses hash which sends to any healthy node. There is no typical round-robin. To stick to a certain BIG-IP, the source affinity will be required.

"The hash is used to route traffic to healthy backend instances within the backend pool. The algorithm provides stickiness only within a transport session. When the client starts a new session from the same source IP, the source port changes and causes the traffic to go to a different backend instance."

https://learn.microsoft.com/en-us/azure/load-balancer/distribution-mode-concepts

By default, Azure Load Balancer uses a five-tuple hash.

The five tuple includes:

• Source IP address
• Source port
• Destination IP address
• Destination port
• IP protocol number to map flows to available servers