I already posted this on the AWS forums without success (https://forums.aws.amazon.com/message.jspa?messageID=502441). I'm wondering if I'll be more lucky here.
We have an internal DNS setup that uses the official AWS EC2 DNS 172.16.0.23 as a forwarder.
Intermittently the forwarder stops resolving AWS hostnames with their internal IPs and returns the public IPs instead. A script in the crontab checks the DNS every minute and restarts the service to clear the cache when needed. The host against which we check for correct name resolution is an RDS instance. DNS software is Bind version 9.7.0.
The problem is not unique to this instance or account since we had the same problem on another instance from another account. Also, this particular instance has been shut down and restarted so it doesn't seem to bee any hardware issue since shutdown/restart should migrate instances to different hardware.
Same (unsolved) problem here:
https://forums.aws.amazon.com/thread.jspa?threadID=76515
Does anyone else have this problem? Can someone point me in the right direction for a solution?
Thanks,
Jeremy
Best Answer
DNS in a VPC works as follows:
When an instance starts, it registers with the DNS forwarder in the subnet.
Thereafter, when any other instance in the VPC queries any hostname for that instance, it will return the private ip.
When the instance is stopped, the record with the forwarder will expire.
Thereafter, when any other instance in the VPC queries any hostname for that instance, it will return the private ip. This is because the local DNS forwarder doesn't have a record and forwards the request to the primary DNS servers for Amazon.