What is One-arm Configuration?
One-arm configuration is one method of deploying a load balancer. In this setup, the client, server, and load balancer are connected to the same communication path. This means the client and server can communicate directly, while the load balancer is connected as an off-branch to the network. Another setup method is the in-line configuration, where the load balancer is placed directly on the communication path between the client and server, making it impossible for the client and server to communicate directly.
When deploying a load balancer in a one-arm configuration, the server’s default gateway typically needs to be set to point to the load balancer. If this configuration is not properly set, communication issues may arise. For example, while client requests pass through the load balancer, the server’s responses may bypass it. This mismatch between the client’s destination IP address (in the request) and the response's source IP address causes the client to reject the response.
F5 BIG-IP includes the SNAT (Secure Network Address Translation) feature to resolve this issue. By configuring SNAT properly, server responses are guaranteed to pass through the BIG-IP load balancer, regardless of the server's default gateway settings, ensuring seamless communication.