A Virtual Server Cluster (VSC) is a High Availability (HA) and Highly Scalable (HS) group of servers that all handle the same tasks appearing to be only one server.  Common applications of a VSC is web serving and Client/Server server-side applications.

With two Firon 8.1 Security Servers, HA edition, simple, cost-effective VSCs can be built and scaled to meet the demands of today's network applications.

The typical VSC looks something like this three-tier diagram:

The design and layout of Tiers 2 and 3 do not affect Tier 1 at all.

On Tier 1 we have two Firon 8.1 Security Servers HA edition with one running as the primary and the secondary as a automatic failover.  The Load Balancers automatically detect when application servers in Tier 2 fail or are taken off-line and balance the load across the remaining servers.

On Tier 2 we have any number of application servers.  The response of the application servers will scale up to the full performance potential of the cluster as the load increases.  More application servers can be added as needed to increase the cluster's performance potential.

On Tier 3 we have the backend services needed to support the application servers.  Any number of backed servers can be ran in Tier 3.

There are three different architectures for a VSC:  1. VS/NAT (Network Address Translation, the above example); 2. VS/TUN; and 3. VS/DR.

A typical VS/TUN (Tunnel) looks like this (Tier 3 removed for clarity):

The principle difference between a VS/NAT and VS/TUN is the Load Balancers transmit incoming request to the application servers via an IP Tunnel.  In turn each application server responds to incoming requests by routing the response back possibly via a separate link to the Internet than the one the request came in on.  This is one of the two important features of the VS/TUN that separate it from the VS/NAT:

1. The response can be sent back via a separate link.
2. The application servers can be geographically separated.

These features combined make the VS/TUN more desireable in environments where more data is sent back to the Internet than is received in the corresponding request.  Each application server can have it's own link to the Internet, reducing the bottleneck of the data returning to the client(s).

The third VSC architecture, the VS/DR (Direct Routing), looks like this (Tier 3 removed for clarity):

The VS/DR is exactly like the VS/TUN except each application server and the Load Balancers must be connected via the same physical link.  Typically the Internal Network doesn't impede the scaling performance of the VS/DR (usually the internal network will be faster or at least as fast as the incoming link), but it does limit the routing of requests to one physical network segment.  Because of this restriction the VS/TUN is generally preferred to the VS/DR.