Load balancing : Load balancing among local servers : Defining your pool of back-end servers : Monitoring your servers’ responsiveness
Monitoring your servers’ responsiveness
Tests for server availability (called “server health checks” in the web UI) poll web servers that are members of a server farm to determine their responsiveness before forwarding traffic. Server health checks can use:
TCP connections
TCP SYN (half-open connection),
email (SMTP, POP3, IMAP)
To most accurately determine whether your servers are available, if possible, configure FortiADC to use the same protocol to monitor your servers that clients will use to connect to them.
The FortiADC appliance will poll the server at the frequency set in the Interval option. If the appliance does not receive a reply within the timeout period, and you have configured the health check to retry, it attempts a health check again; otherwise, the server is deemed unresponsive. The FortiADC appliance reacts to unresponsive servers by disabling traffic to that server until it becomes responsive.
If a web server will be unavailable for a long period, such as when a server is undergoing hardware repair, it is experiencing extended down time, or when you have removed a server from the server farm, you may improve the performance of your FortiADC appliance by disabling connectivity to the web server, rather than allowing the server health check to continue to check for responsiveness.
To configure server health checks, go to Server Load Balance > Resources > Health Check. To use them, select them when configuring a server pool.