A cluster is a group of LoadMasters working in conjunction. Clusters can also be non-LoadMaster entities using TCP or ICMP health checks. GEO clustering is a feature mainly used inside data centers. Health checks are performed on a machine (IP address) associated to a specific FQDN, using the containing cluster server, rather than the machine itself.

You can add a maximum of 18 GEO clusters.

In terms of GEO, a cluster is a GEO LoadMaster polling another device for health checks. For example, a GEO LoadMaster can poll a firewall on a site in front of Real Servers. If the firewall is up, it is assumed that everything behind the firewall is up too. If the health check to the firewall fails, the Real Servers behind the firewall are marked as down.

GEO LoadMasters can be used with a normal LoadMaster as a cluster. There are two methods for clusters:

  • First, the LoadMaster can be polled for health checks (same as a firewall or any other device). If this LoadMaster health check fails, everything behind the LoadMaster is marked as down.
  • Second, you can use cluster checks. In this case, the GEO LoadMaster polls the LoadMaster and the LoadMaster informs the GEO LoadMaster which Virtual Services are up.

Clusters can be added, modified and deleted from the Global Balancing > Manage Clusters menu option.

The following diagram helps identify common cluster devices, which include edge routers, firewalls or load balancers. Health checking these devices can summarize the availability of the devices behind their services.

  • ISP Router: Checking the ISP’s edge router will quickly allow the detection of loss of ISP network connectivity
  • Firewall: Checking the firewall will confirm that the ISP network is available and provides visibility to the first arm of equipment located at the data center
  • LoadMaster: Checking a load balancer will confirm if the ISP is available, the network infrastructure is available and the Real Servers are responding as expected