This section lists the troubleshooting techniques of a health monitor.
For general monitor definitions see the following links:
Reasons a Server Can Be Marked Down
Manually Validate Server Health
General Health Monitor Details
The following are the details of the general health monitor:
Multi-Pool — A server that exists in multiple pools will receive health checks for each pool it has membership within. If the pools are on the same Service Engine and configured with the same health monitor, then the system will not perform redundant monitoring.
Disabled — Health checks are not performed for disabled servers, servers within a pool that are not assigned to a VS, or attached to a disabled virtual service.
Scaled SEs — When scaling out a virtual service across multiple Service Engines, the servers will receive active health checks from each SE for the virtual service. If one SE marks a server as up, it will be included in the load balancing. If a second SE is unable to access the server, it will mark it down and not send traffic to that server. From the Controller UI, the server health icon can flip intermittently between red and green (or other colors). The status flipping is due to the frequency when SEs report their status to the Controller.
SNAT IP — If a SNAT IP is configured for a virtual service (see virtual service), the active SE will send monitors from the SNAT IP address. If a SNAT IP is not configured, the active SE initiates monitors from its interface IP. The standby SE will always send monitors from its interface IP.
Standby SE — By default, the standby SE will send health checks. This behavior can be changed from the CLI for the Service Engine Group of the SE.
Send Interval — By default, Avi Load Balancer sends checks based on the frequency defined by a monitor's Send Interval timer. However, if you add a new health monitor or a new server to a pool, or if there is a positive monitor response received after a server that has been marked down for a long time, Avi Load Balancer will quickly send additional checks. For instance, if a new server is added to a pool with a monitor set to query every 20 seconds, and requires 3 consecutive positive responses, the server will not be marked up for nearly one minute. In this example, when the new server is added to the pool, Avi Load Balancer will send the first 3 checks immediately to the server. The server will respond, potentially marking the server up within one or two seconds. The system performs the subsequent checks at the interval specified by the Send Interval setting of the health monitor.
Port Translation Enabled — If port translation is enabled:
The server ports targeted by the virtual service has to be defined.
If active monitoring is needed, but the ports to be monitored are not explicitly defined, the Avi Load Balancer infers them from the defined server ports (on a per-server basis).
Port Translation Disabled — If port translation is disabled:
If active monitoring is needed, but the ports to be monitored are not explicitly defined, the Avi Load Balancer does not infer them automatically from the defined server ports.
You must add a health monitor for each port on the servers needing to be monitored.
