How to set up a fault-tolerant system at the DNS level?

Question

Domain Name System

Hello,
I purchased a domain on cheapname and set up the use of my own ns servers in my account:
ns1.example.com
ns2.example.com
by roundrobin? How to configure fault-tolerant ns servers (when the first one fails, the second one picks up its functions)?
After DNS there are load balancers.
2) What would you recommend to use the DNS server (applicuhu)? Is it possible to set up health checks on it - so that when one of the balancers crashes, ns sends requests only to other balancers?
Thanks

Answer 1

1. There will be, but there will be some delay for the user when trying to access the failed one (like 2 attempts for 5 seconds - check). After the first successful resolution, it will continue without delay.
2. The simplest option is a helscheck script for two dozen lines, which will rewrite records using the API (it's easy). However, in case of connection problems, you can incorrectly rewrite it so that it does not happen - you need to complicate the logic.

Answer 2

There are quite a few caches on the user side. Starting from the browser, ending with the Internet provider.
You can forget about 100% availability. You can shorten the TTL on DNS servers. If you're lucky, the user will pay attention to them.