This topology focuses on providing a load balanced service with minimal hardware requirements. Real-Servers may be added as additional serving resources are required. A sample configuration is available.
The Linux-Director acts as the gateway router for the network and load balances traffic using LVS. The linux-director would typically be fitted with two Network Interface Cards (NICs). Optionally, the linux-director may have packet filtering enabled to control the traffic which is able to enter and leave the server network. When configuring LVS to forward packets using NAT, RFC 1918 [offsite] private addresses may be used to reduce the number of externally routable IP addresses required as the return path for the Real-Servers is through the linux-director.
When a linux-director receives a connection from an end-user it makes a decision on which Real-Server to forward the connection to. All packets for the life of this connection will be forwarded to the same real-server so the integrity of the connection between the end-user and the real-server is maintained.
Ldirectord monitors the health of the real-servers by periodically requesting a known page and checking that the response contains an expected string. If a real-server fails then the server is taken out of the pool of real-servers and will be reinserted once it comes back on line.
The Real-Servers may run a variety of services including The Apache HTTP Server [offsite]. Additional real-servers may be added to the network as extra capacity is required.
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