We have our server infrastructure in an externally hosted IaaS environment and normally this works really well.
However, occasionally we have a problem with the dedicated data link to our IaaS which then completely cripples us.
The problem is that we have a number of external services (such as Office 365) which will continue to be accessible in this scenario (via a separate Internet Breakout), however, currently this doesn't work, as whenever we lose access to the DNS servers, we lose DNS any so therefore any ability to contact Office 365.
This wasn't a problem previously as we had a backup DNS server (also a DC) outside of the IaaS environment, however we want to decommission this server now and the ideal would be not to replace it.
I recently started to decommission this local server and thought I would mitigate this problem by adding a couple of Google DNS servers after the primary and secondary (the primary and secondary are IaaS DC's running DNS).
My understanding was that the Google DNS would only be queried if the primary and secondary addresses didn't respond, however, in practice it doesn't seem to have worked like this and there have been a number of problems that seem to be internal DNS name resolution issues.
I have now temporarily reverted back to the old configuration, but am still keen to get rid of this on-site hardware.
What am I doing wrong? Am I misunderstanding how DNS works in this situation?
How can I mitigate for the situation where the link to IaaS goes down without needing local hardware and without losing access to our external systems that should still be accessible from the Internet breakout regardless of whether access to IaaS is available?
I hope this question is clear? Please ask for separate clarification if not!