To start with, I don't know jack about DNS servers. I have been stuck with resolving a problem with a DNS-Server because I discovered a problem with one of our systems and determined that it was caused by the DNS resolution.
We use an external web service for some critical operations. Our software is in constant communication with the external service. The external provider actually has two hosts (each with its own IP Address) that provide this service, and changes the DNS records so that the one name (call it criticalservice.example.com) always resolves to the currently active host.
Our software periodically checks the connection to the external system. As long as the name resolves to the correct active host, all is good. However, the provider occasionally changes the active host (and the DNS record to match.) Our system keeps the old IP address for the host name cached until the TTL expires. Until it expires and gets the correct IP address, our system reports a communication error and can't be used. Once the IP address catches up, our system automatically reconnects and goes back to work. The time it spends offline can be anything up to the full TTL period - our DNS server seems to use 3600 seconds as the default TTL.
The service is not critical as in life and death, but critical in the sense of not being able to notify people who might be needed to deal with a life and death situation as quickly as possible. Given that, we would really like to shorten the time the system spends waiting for the DNS TTL.
The DNS-Server from the ISP has a very short TTL for criticalservice.example.com, and the ISP recommends either using their DNS directly or using a very short TTL on our internal DNS Server.
Since our DNS server is also an Active Directory domain server, I don't think that changing the TTL for the entire DNS server is a good idea.
The best idea I have would be to set a TTL only for criticalservice.example.com.
How would I create a DNS entry for criticalservice.example.com in our Windows 2008 Server that would limit the cache time to less than 1 minute, but still allow our DNS server to pick up the correct IP address from the ISP DNS Server? As far as I can tell, I can only set a TTL if I add a record that maps the name to the IP address - and I can't do that because the IP address changes.
Alternatively, could I do something to the DNS client on our machine that uses criticalservice.example.com so that it bypasses our DNS Server, but only for criticalservice.example.com?
Additional info: nslookup -qa=A criticalservice.example.com local.dns.server returns TTL of 3600 seconds. nslookup -qa=A criticalservice.example.com isp.dns.com returns TTL of 15 seconds.
