Zimbra Preauth Router: 0 downtime migrations

At ZBox Mail we are faced with migrations from production Zimbra servers to Our Cloud Platform. Some times the source servers are small enough that you can bring down the service for a couple of hours, migrate all the mailboxes and start again in the new home.

But luckily for us we are migrating a lot of big platforms. For big we mean over 1,000 mailboxes and Terabytes of mail data. And One Does Not Simply migrate this in a couple of hours.

So we came up with this procedure to do a 0 downtime migration:

  1. Setup a split domain between the 2 platforms, customer and ours,
  2. The company must announce that a migration is in place, and for as long as the migration take place, only the Webmail is allowed
  3. Every day we migrate a group of N mailboxes.
  4. Repeat 3 until finish
  5. Celebrate

The exclusive use of the Webmail is paramount. This way we can use Zimbra Preauth Router an let it redirect the user to the old or new platform.

The way the Zimbra Preauth Router (ZPR) works is by replacing the standard Zimbra Login Page, and decide where the user should be redirected. The steps followed are:

  1. The user authenticate against ZPR,
  2. ZPR looks into a DB file for an entry for this user. Any user listed was migrated.
  3. If it’s a migrated user, ZPR redirects him to the new platform, if not, to the current platform.
  4. Thanks to Zimbra Preauth the user enter directly to the Webmail, without the need of another validation.

This way the users doesn’t need to learn a new URL and the migration process is mostly transparent for them.

For ZPR to works you need to configure Preauth Keys for the Domains, as explained at the Zimbra Wiki

All the information on how to install and use ZPR can be found here: https://github.com/pbruna/zimbra_preauth_router

As always, all ideas are welcome.

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