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It seems that my database instance had a failover in the middle of the night and changed IP address. My webserver connects to it remotely. The IP address, which is found from Amazons DNS service that contains its internal IP, doesn't seem to have updated with that new address. However if I connect from my local machine the correct IP is returned and I can connect and also if I use that IP from my webserver rather than the host name it also connects okay.

How can I get Amazon's DNS to return the correct external IP to my webserver?

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Additionally nslookup returns the correct IP but ping does not. – user144453 Nov 7 '12 at 15:58
Did someone manually set an IP in /etc/hosts? – ceejayoz Nov 7 '12 at 17:53
You could spin up a new instance ("restore to point in time" creates a new instance) and point at it instead if you're having DNS propagation issues. – Jason Floyd Nov 9 '12 at 6:35

If you run an RDS instance in AWS, you're given an "endpoint" address in the properties for that instance. So in the case of running a Multi-AZ RDS, whenever you have failover the pointer will be shifted to address the failover node in another AZ. However, you won't have to update your applications when they point to that endpoint.

But if you query the IP of the endpoint and address your applications to that, you're destined to have issues at some point down the road; not only might that IP change in the case of failover, but it might even change during regular maintenance windows, or if your instance is rebooted, or migrated to a different Xen host within AWS's architecture.

The endpoint is, I am told, essentially an ELB address itself. When critical errors occur in your RDS, the AWS system will see your unhealthy instance, drop it from the ELB, and add your failover node, as well as kick in some scripts to promote the node, I'm sure.

You may also want to see this answer: Does AWS RDS endpoint change in the event of instance failure>

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