Should I monitor DNS separately, or is an HTTP check enough?
Q: If my site responds, doesn't that prove DNS works? Why add a separate DNS monitor?
A: Usually yes — until it isn't. A reader running only HTTP checks got a clean bill of health while a chunk of users couldn't reach the site at all. The cause: their registrar pushed a config change that dropped one of two authoritative nameservers. Resolvers that cached the good one were fine; resolvers hitting the dead one failed.
Their HTTP monitor resolved through a healthy nameserver, so it stayed green for the entire 3-hour event. Support tickets revealed roughly 18% of traffic was affected.
They added a DNS monitor that queries each authoritative nameserver directly and checks the returned records match expected values. The next registrar hiccup was caught in 4 minutes.
The follow-up: also alert on unexpected record changes, not just resolution failure. A wrong-but-resolving record (a hijack or fat-fingered edit) is worse than a timeout, and a plain up/down check won't see it.
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Should I monitor DNS separately, or is an HTTP check enough?
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