Performing the migration

The gist of it:

1. Set up the new Pleroma server
2. Copy the pleroma folder into your Pleroma repo (merge them)
3. Copy the mastodon folder into your Mastodon repo (merge them)
4. Shut down Mastodon
5. Perform the export on the Mastodon server (rake migrator:export)
6. While this runs, point your domain name DNS to the new server
7. Copy the exports from the Mastodon server to the Pleroma server
8. Perform the import (mix migrator.import)
9. ???
10. Profit

You can skip steps 4 & 6 to test this without downtime. I highly recommend you do so. Don't expect this to work the first time. Verify the exports manually.

See the do_migration.sh script for ideas about making it reproducible.