A zero downtime migration is moving a website to a new host without visitors seeing any interruption.
A zero downtime migration moves a website from one host to another so smoothly that visitors never see an error, a maintenance page or missing content. The old site keeps serving visitors while the new copy is built and tested, and traffic only moves across once the new server is ready.
The trick is that a website isn't really moved. It's copied. For a while, two working copies exist: the live one on the old host and a new one on the new host. Changing DNS then decides which one visitors reach.
How a zero downtime migration works
- Copy the site: files, databases and email are copied from the old host to the new one.
- Test on the new server: the site is checked using a temporary URL or a hosts file entry, without changing DNS.
- Lower the DNS TTL: a day or two before the switch, the time to live on the domain's records is lowered so the change spreads faster.
- Final sync: anything that changed on the old site, such as new orders or posts, is copied again just before the switch.
- Switch DNS: the A record or the nameservers are pointed at the new server.
- Keep the old host running: while DNS updates, some visitors still reach the old server, so it stays live until traffic has moved.
Why zero downtime migration matters for your website
Even a short outage during a move can cost sales, interrupt search engine crawls or lose form submissions and emails. A careful migration means visitors and search engines notice nothing, and you can switch back quickly if something unexpected turns up.
The tricky parts of a zero downtime migration
- Busy, dynamic sites: shops, forums and membership sites change constantly. Anything written to the old database after the final sync can be missed, so pick a quiet hour and sync immediately before the switch.
- Email: messages can arrive at either server while DNS updates. Leave the old mailboxes in place for a few days and check them.
- SSL certificates: the new server needs a valid certificate before traffic arrives, or visitors see warnings.
- Hardcoded settings: old IP addresses or file paths in configuration files can break things after the move.
Take a fresh backup on the old host before you start, so you always have a clean copy to fall back on.
Zero downtime migration vs a standard migration
In a basic migration, the site may be taken offline, copied and brought back up on the new host, leaving a gap. Zero downtime is the same work done in a different order, with testing before the switch instead of after it. AblePage offers free website migration by engineers on every plan, and once you've moved, automatic daily JetBackup backups start protecting the new copy.