Cheap IP takeover
Directing traffic to one of several machines is fairly straightforward when using round-robin DNS. But what happens when one of those servers becomes unavailable? Here's one scheme for monitoring the health of another server, and standing in for it if it fails.
First, we need to make a distinction between the server's "real" IP address, and the IP (or IPs) from which it actually serves public content. For this example, we'll be referring to two servers, Pinky and Brain. Pinky uses the IP address 188.8.131.52 for its "real" IP on eth0, and also has an IP alias of 184.108.40.206 on eth0:0. Brain uses 220.127.116.11 on eth0, and 18.104.22.168 on eth0:0.
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