Planning a low-downtime hosting migration
DNS, mail, cron and redirects cause more migration pain than the application itself. Inventory them first.
Moving an application between hosts is rarely the hard part — the code copies over, the database imports, the site loads. What breaks is everything attached to the old environment that nobody wrote down: the mail relay, the nightly job, the redirect map, the API allowlist keyed to an old IP address.
Inventory before you touch anything
Spend the first day writing down what exists, not moving it.
- Every DNS record, including mail, verification and subdomain records you did not create.
- Scheduled jobs, what they do, and how you would know if one stopped running.
- Outbound integrations and any that authenticate by IP address.
- Existing redirects and rewrite rules — these carry your search visibility.
- TLS certificates, their issuers and their renewal mechanism.
Lower the DNS time to live early
Drop the TTL on the records you plan to change to a few minutes, at least 48 hours before cutover. It costs nothing and turns a potentially day-long propagation tail into a short window — and it means a rollback is also fast.
Rehearse the cutover, then do it for real
Run the migration once into the new environment while the old one still serves traffic. Test the site there using a hosts-file override, verify forms and mail, replay a few critical user journeys, and time the whole sequence.
For the real cutover, put the source into read-only mode if the application supports it, sync the final delta, flip DNS, then watch error rates and mail delivery rather than declaring victory once the homepage loads.
The week after
Keep the old environment running but firewalled for at least a week — it is the cheapest rollback you will ever buy. Watch for 404 spikes that reveal a missing redirect, mail bounces that reveal a missing sender record, and any integration that quietly stopped because the source address changed.
Low-downtime migrations are won in the inventory and the rehearsal. The cutover itself should be the least eventful part of the week.
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