Each machine has it's own IP address, but in addition there are a pair of IPs for the SERVICE that are managed by Heartbeat. The round-robin DNS entry points to the service addresses, not the "primary" addresses of each node.
When one node goes down, Heartbeat on the other node causes it to take over the failed node's service address. This minimizes the time where the resolved address points to a dead node. so the window for failure is narrowed significantly. We've used this for DNS server, LDAP servers, and simple web servers with good results.
This is NOT an absolute fail-proof way of doing it, but it's easy to implement and is "good enough" in many cases. We've had some situations where Heartbeat didn't detect node failure quickly, but overall we've gotten acceptable results.
Your mileage may vary! -- Jay Leafey - jay.leafey@xxxxxxxxxxxx Memphis, TN
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