GEO utilizes Layer 3, Layer 4 and Layer 7 health checks to monitor the availability of the IP address end-points and clusters. In the case that one of the servers does not respond to a health check within the defined time interval, for a defined number of times, the weighting of this server will be reduced to zero. This zero weighting has the effect of removing the endpoint from the FQDN configuration until the endpoint is back online.

Health checks occur from the LoadMaster. Therefore, it is important to make sure that the LoadMaster has access to each cluster and IP address. If all checks fail, ensure that the default gateway is correctly operating.

The following table describes the different health check options available for GEO FQDNs:

Layer

Type

Description

None

None

No check occurs

Layer 3

ICMP

The LoadMaster sends ICMP echo requests (pings) to the endpoints. An IP address end-point fails this check when it does not respond with an ICMP echo response in the configured response time for the configured number of retries. This is only a relevant health check when the endpoint target is not a LoadMaster.

Layer 4

TCP

The LoadMaster attempts to open a TCP connection to the IP address end-point on the configured service port. The server passes the check if it responds with a TCP SYN ACK in the response time interval. In this case, the LoadMaster closes the connection by sending a TCP RESET. If the endpoint fails to respond within the configured response time for the configured number of times, it is assumed down.

Layer 7

Cluster Checks

A health check is performed on the IP address of the cluster. Different types of clusters can be defined. The health checks differ for each type:

Default Cluster Type: An ICMP Ping or TCP Connect health check (depending on what is selected in the Manage Cluster options) is performed.

Remote LM Cluster Type: An SSH connection is attempted. The native LoadMaster statistics are obtained and matched against the FQDN Real Server. If a matching Virtual Service IP is not found, the list of Real Servers cluster is marked as down. Permission to connect must be granted on the LoadMaster.

Local LM: This method is required if a LoadMaster is co-located with the GSLB Feature Pack for health checks to function correctly.

If the Checker type is set to Cluster Checks and the cluster Type (in Global Balancing > Manage Clusters > Modify > Type) is set to Remote LM, you must also select the associated Virtual Service from the Mapping Menu drop-down list.

Note: If Virtual Services are not displayed in the drop-down list, ensure that both LoadMasters are able to access each other. The remote GEO partner must be configured in Certificates & Security > Remote Access.

The Mapping Menu drop-down list displays a list of Virtual Service names (where available) and Virtual Service IP addresses from that LoadMaster. If there are multiple Virtual Services using the same port, there is an entry in the drop-down list for the Virtual Service with up to five ports shown and other individual entries with each port. Select the Virtual IP address and port (or ports) that is associated with this mapping. If a Virtual Service with multiple ports is selected, the health check checks all Virtual Services with the same IP address as the one selected. If one of them is in an “Up” status, the FQDN shows as “Up”. The port does not come in to consideration. If a Virtual Service with one port is selected, the health check only checks against the health of that specific Virtual Service when updating the health of the FQDN.