Cluster hierarchies

About clusters

A cluster is a group of two or more proxy-cache servers (parents) or firewalls over which the NetCache appliance distributes requests. You can specify multiple proxy-cache servers or multiple firewalls to be members of a logical cluster. The cluster acts as a parent to the NetCache appliance you are configuring. Cluster hierarchies load balance by distributing requests across multiple parents and provide failover if any member of the cluster goes down.

Cluster load balancing

Load balanced requests are distributed from a child cache across multiple parents. Load balancing is advantageous for networks in which the volume of requests for service is difficult to predict.

For load balancing to occur, at least two cluster members must handle the same protocol. The NetCache appliance on which you are configuring the hierarchy uses a proxy-selection algorithm to determine which hierarchy member in the cluster can best handle the request. The appliance then sends the request only to that hierarchy member.

Note
Load balancing requests among NetCache appliances that vary in capacity can overwhelm a smaller cluster member. Load balancing is most effective among members of like capacity.

Cluster failover

Failover provides a mechanism for two NetCache appliances, third-party proxy-cache servers, or firewalls to serve the same functionality. If one member of the cluster goes down, the NetCache appliance you are configuring sends the request to another cluster member.

The NetCache hierarchy feature can be set up to monitor direct connectivity and provide failover to another cache if an Internet connection goes down.

For more information, see Custom rules for distributing requests.

Cluster hierarchy configuration

The following illustration shows a cluster hierarchy configuration. Load balancing and failover occur automatically between cluster members.

Note
Proxy-cache servers or firewalls that handle multiple protocols can be configured as members of more than one cluster in a hierarchy.