How to smoothly change domain servers?

Question

I'm changing server accounts. My company has a domain name hosted with GoDaddy, let's call it www.example.com. This hosting account is a shared hosting account. They also have another domain name within it (sub-domain?) that ONLY handles registration. It doesn't even have a front-end, just PHP and mySQL. Let's call that domain - registration.example.com.

My company purchased a VPS account from GoDaddy and wants me to move ONLY the registration.example.com domain over to the VPS for better performance, security, etc.

I copied the content over, but now my main questions are - How do I transfer the domain to use this new VPS without any downtime? Do I just change the nameservers? Is there a safe way to test this? Can I fallback instantly in case it doesn't work as intended?

Answer 1

To do what you are asking all you need to do is open the domain record record for registration.abc.com and change it from point to the shared server to pointing to the VPS by changing the A record from the shared servers IP address to the VPS's IP address.

As for no downtime by keeping the sub domain in place on the shared hosting server as well for the short term this will mean that while the old IP address is still cached users will still have access to it using the old shared server and as cached copies of the DNS entry expire the users will be directed to the new server using the new IP address. This should be completed at most 48-72 hours after the DNS change depending on your time to live settings and any upstream caching that is being done.