Topologies

High Capacity High Availability and Load Balancing

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.

• Linux Directors

  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.

  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.

• Real Servers

  The Real Servers may run a variety of services including The Apache HTTP Server. Additional real servers may be added to the network as extra capacity is required.

Copyright © 2000-2005, Horms
Last Updated: Tue May 17 17:37:24 2005 +0900

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