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I'm building an application that requires high-availability. We currently run: 4 webservers, 2 varnish servers (both with Pound for SSL proxy), 3 Cassandra nodes.

The varnish servers are used as entry points for the system. We want to configure everything that Varnish A always works, until failure, then Varnish B should receive the requests and distribute them to the webservers.

As Varnish A and Varnish B are not in the same DC and some other demands of our company it wasn't possible to use some Heartbeat like system to use a virual IP.

We decided to solve it with the CNAME record of our website.

We now have something like this:

hac.domain.com CNAME hac1.domain.com (TTL = 60s)

hac1.domain.com A 12.34.56.78 (TTL = 86400s)

hac2.domain.com A 22.33.44.55 (TTL = 86400s)

Our idea was to swap the hac.domain.com CNAME record as we detect a failure. This gives us a maximum downtime of roughly 2 minutes (if no DNS caches are still redirecting to the wrong server). Acceptable for our use case.

The main question: How to detect the failure in a redundant way and prevent false-positives?

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2 Answers 2

up vote 1 down vote accepted

I started to use Route 53 in combination with CouldWatch of Amazon to provide the service level I need. Exactly what I needed!

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You may use heartbeat to detect failure and run a script to change dns. You need to use a dedicated connection for heartbeat.

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