Topologies

Streamline High Availability and Load Balancing

This topology combines the function of Linux Directors and Real Servers into the same hosts, so that high availability and load balancing can be achived with just two nodes. A sample configuration is available.

• Linux Director / Real Servers

  At any given time one of the hosts is the active 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 both the localhost and the other node using LVS. The two nodes 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 (itself or the other node) 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 the services on both nodes by periodically requesting a known page and checking that the response contains an expected string. If a service fails on a server, then the server is taken out of the pool of real servers and will be reinserted once it comes back on line.

  The return path for connections is directly onto the local area network, or gateway router. As direct routing is used in this configuration, the return packets do not need to pass back through the load balancer.

  The servers may run a variety of services including The Apache HTTP Server. Additional real servers (that do not also act as linux directors) may be added to the network as increased capacity is required. However, there are other topologies that scale better to higher bandwidth requirements.

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

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