Can you accidentally cause significant downtime by making a typo in a CNAME or A rec?

Question

Let's say I need to change the CNAME for my subdomain test.mysite.com.
I want it to go to a load balancer endpoint 'aws-my-endpoint.com'.
But in creating the CNAME, I type it wrong. e.g. 'aw-my-endpoint.com'
Since it's possible that a client can cache DNS for up to 48hrs (despite what the TTL setting is), could this cause test.mysite.com to be down for 48hours? Even though I immediately fix the CNAME after noticing the typo?

peter n · Answer

Yes. I've seen with ELB to ALB transitions where clients still hit the ELB, sometimes for days. Most traffic however, usually take a few minutes to port over.
But with a non-existent target (like a typo in your case), there's a chance it would be faster since clients typically wouldn't cache a failed response. The resolvers may cache but they'd respect the TTL specified on the record. There's more on this behavior on this thread

Can you accidentally cause significant downtime by making a typo in a CNAME or A rec?

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