You can send a UDP datagram to the server, then match the server’s response against the expected response data.
The default system UDP health monitor will detect failure only when ICMP unreachable is received. It will keep the server UP until it receives ICMP unreachable for the defined UDP port. Hence it does not detect the failure if the,
UDP health monitor request gets dropped or blackholed before reaching the server.
ICMP unreachable response packets are being dropped.
Backend UDP server does not send ICMP unreachable.
To configure a UDP health monitor, choose UDP option from the Type drop-down menu.
To configure the UDP health monitor,
In the Health Monitor Port field, specify a port that must be used for the health check. When this field is blank, the default port configured for the server will be used. When it is specified, clients may be directed to a different port than what is monitored.
Use the section Client Request Header and Server Response Data to input a UDP request and the keywords to look for in the UDP response.
Configuring Server Maintenance Mode
Custom server response can be used to mark a server as disabled. During this time, health checks will continue, and servers operate the same as if manually deactivated, which means existing client flows are allowed to continue, but new flows are sent to other available servers. Once a server stops responding with the maintenance string it will be brought online, being marked up or down as it normally is based on the server response data.
This feature allows an application owner to remove all connections from a server prior to taking the server offline without the requirement to log into NSX Advanced Load Balancer to first place the server in disabled state.
Under Maintenance Server Response Data enter the match for a keyword to find in the first 2kb of the server header and body response. If the defined string is seen in the server response, the server is placed in maintenance mode. The health checks will continue, and servers operate the same as if manually deactivated, which means existing client flows are allowed to continue, but new flows are sent to other available servers. Once a server stops responding with the maintenance string, it will be noticed by the subsequent health monitors and will be brought online, being marked up or down as it normally would, based on the server response data. A manually deactivated server does not receive health checks and is not automatically re-enabled.
See the Detecting Server Maintenance Mode with a Health Monitor for an example configuration.
