Gurus: Can I setup multiple name servers at different hosts for 1 domain name?
I have been trying to think of an inexpensive way to produce some level of network redundancy for a few clients.
What I was wondering is this:
If I was to have two seperate hosting accounts at HostA and HostB which would be using different Data Centers. And for the domain I setup 4 nameservers: NS1.HostA.com, NS1.HostB.com, NS2.HostA.com and NS2.HostB.com
If HostA went down would the domain automatically resolve to HostB?
Of course, if this does work I'm not sure how I would keep the Databases sync'd.
DNS queries would automatically fail over to the two DNS servers at hostb. Since DNS records are cached, HTTP traffic won't automatically fail over to the server at hostb unless you set an extremely low TTL on the records returned from both datacenters. Even then, there are enough idiots with DNS servers that don't properly follow TTLs that it won't work right for everyone.
What other methods are available to provide the desired functionality.
I know a number of resellers have accounts setup on multiple hosts. But if one host goes down, the only way to switch (that I know of) to the working host would be to do a DNS change on the domain - which by the time it took effect the first host would probably be back online.
No, no problem with that. I'm using two servers in different locations to host DNS for several thousand domains, support several thousand clients doing recursive queries, and perform RADIUS authentication. The five-minute load average on the primary server right now is 0.03. Gotta love djbdns. :)
The TTL value tells resolvers how long that can continue serving a cached copy of a record before they need to go out and get the answer from an authoritative server again. If a resolver ignores your 30-second TTL, for example, it might continue serving old, inaccurate data for several hours, even after you've updated the record to point to the backup server.
Hmm, I suppose nothing can be done then from the server's point of view to force poorly coded resolvers to refresh. Any idea how common this is? I could live with 90% of the world resolving according to actual TTL.
It's definitely a small percentage... Just something that I've noticed when doing cutovers in the past. Even after all of the old records should've expired, hits still trickle in to the old IP addresses. If you're looking for actual names of software, I've seen Lotus Notes mail servers cache MX records far beyond their TTLs.
nuance9: All of the other ways that I've heard of to do failover between different data centers require specialized hardware and/or fancy routing techniques. I'm not very knowledgeable about the options here; sorry.