Managing DNS and subdomains during a migration
Just a few minutes of misconfigured DNS is enough to generate lost traffic and frustrated customers. Here's how to migrate without any service disruption.
- Lowering the TTL one to two weeks before the migration speeds up propagation from 48h to a few minutes
- Every subdomain (mail, API, blog) must be inventoried before touching the DNS
- Global propagation takes 24 to 48h even with a properly lowered TTL
- Never touch the MX records without coordination, or you risk losing your emails
Why DNS is the invisible but critical infrastructure
DNS is what lets your visitors find your website. When you change hosting provider or server, the DNS records must be updated to point to the new address. Without careful management, some users will keep loading the old version or land on an error page. It's the link between the technical change and the continuity of service as perceived by your visitors and by Google.
Lower the TTL before the migration
The TTL (Time To Live) tells DNS servers around the world how long to remember your record before checking it again. Often set to 24 or 48 hours by default, it should be lowered to 300-900 seconds (5 to 15 minutes) one to two weeks before the migration. Once the migration is verified, raise the TTL back to 24-48h to reduce future DNS load.
Edit the DNS records and check the subdomains
With most registrars (OVH, Gandi, Ionos), DNS management is done through the control panel: the A record points the main domain to an IPv4 address, while the CNAME often handles the subdomains. Before making any change, precisely note all of your current records (A, CNAME, MX, TXT) so you can reproduce the exact same configuration on the new host. Never touch the MX records without coordination: you would lose your emails during the transition.
Verify global propagation within 24-48 hours
Propagation is never instant. Free tools like whatsmydns.net, mxtoolbox.com or dnschecker.org query public servers all over the world and show the percentage of convergence in real time. With a properly lowered TTL beforehand, expect convergence close to 100% within 24 hours. Also manually test access to the site, the forms and the critical services during this window.
Subdomains: special cases and common pitfalls
- A subdomain www as a CNAME automatically follows the main domain; a www set as a separate A record must be changed individually.
- Check every external service connected to a subdomain (API, integrations, third-party forms) before migrating.
- The new host must cover the domain and subdomains with its SSL certificate, ideally a wildcard.
DNS management is one of the technical steps we handle in every website creation and redesign project, for a seamless switchover.
Chronological DNS migration checklist
Two weeks before: lower the TTL and document all current records. One week before: prepare the exact configuration on the new host and test it. Go-live day: switch the records, wait 15 to 30 minutes, then test from several devices. The following 24 to 48h: monitor propagation every 4 to 6 hours. After 48h: raise the TTL back to its normal value.
Frequently asked questions
How long before the migration should I lower the TTL?+
One to two weeks before, to give the old caches time to expire naturally.
What should I do if propagation is slow after 48h?+
Check with the registrar that the record has indeed been changed at the source, without forcing it, which would only make things worse.
Could my emails be cut off during the migration?+
Not if you don't touch the MX records without coordinating with your mail provider.