Instead of putting all of your eggs in (yet another) one basket, for a site with critical availability requirements I would distribute DNS over multiple providers. If any one provider goes down it is less likely to hurt overall site availability.
Yep. I had been hesitating on moving more domains over to Route53 because I thought the per-zone pricing was fixed at $0.50 per domain, but it actually scales really well. I'm going to move the rest over to Route53 as soon as I have a chance.
We're using Route 53 in production to handle hundreds of millions of queries per month. We're happy with it, and the price is reasonable. Also, service checks with failover is heavenly.
If you don't use namecheap's dns servers, dns requests for your domain do not go to namecheap for redirection. They don't go to namecheap at all. Your specified dns servers get registered with the top level domain servers.
No. The zone file lives on the nameserver (DNS server) which Route 53 provides. Namescheap registers a list of nameservers for your domain with the TLD.
An over simplified example for looking up "news.ycombinator.com":
1. First query the TLD nameserver for all ".com" domains asking for the authoritative nameserver(s) for "ycombinator.com".
2. Next query that nameserver for "news.ycombinator.com".
But, the first entry point is namecheap. The domain is at Namecheap, so it will not find the zone file at Route 53, if Namecheap does not send it there. Right?
No, registrar's are your portal to updating data in TLDs, but those TLDs are each operated separately. .com and .net are operated by Verisign, for example.