This is on top of HN and I don't understand why does no one notice the recommendation of setting the root level CNAME records. While this might work in practice, it is against the DNS standard and causes really weird bugs, like not being able to set up email on the same domain, as for example you cannot set up TXT records.
Unfortunately, solving this problem isn't easy or obvious. You'd need to use ALIAS / ANAME records, which are only supported by a very few DNS providers (DNSMadeEasy, Rage4, Amazon Route53 if you are hosting on S3). Also, you need to set a low TTL to make sure that you are not caching an old cloud instance's IP address.
Unfortunately, solving this problem isn't easy or obvious. You'd need to use ALIAS / ANAME records, which are only supported by a very few DNS providers (DNSMadeEasy, Rage4, Amazon Route53 if you are hosting on S3). Also, you need to set a low TTL to make sure that you are not caching an old cloud instance's IP address.
The best writeup I found about it is here: http://www.dnsmadeeasy.com/aname-records/