This topology enables the maximum throughput through the network as return traffic no longer has to travel through an Linux-Director. This topology builds on the existing routing infrastructure of a network by allowing existing internal routing policies to dictate the flow of outbound traffic. A sample configuration is available.
At any given time one Linux-Director is active, while the other is a hot stand-by. The active linux-director accepts traffic for a virtual IP address. This is the IP address that is advertised to end-users though DNS. Connections are load balanced to the Real-Servers using LVS. The two linux-directors monitor each other using Heartbeat and in the event of the active linux-director failing the hot stand-by assumes the virtual address and the service is maintained. Connections are synchronised between the active and hot-standby linux-directors, so that when a failover occurs existing connections are able to continue.
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.
As the linux-director is not the gateway router for the real-servers, traffic does not have to travel through the linux-director on the return path if direct routing or tunnelling is used. This enables greater throughput as the linux-directors do not have to handle the return packets. It may be possible to send return traffic through different routers and/or uplinks as external connectivity permits.
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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Last Updated: Sat Mar 4 16:33:56 2006 +0900
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