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95 lines
3.5 KiB
ReStructuredText
95 lines
3.5 KiB
ReStructuredText
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Migrating to a new host
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-----------------------
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If you want to migrate chatmail relay from an old machine to a new
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machine, you can use these steps. They were tested with a Linux laptop;
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you might need to adjust some of the steps to your environment.
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Let’s assume that your ``mail_domain`` is ``mail.example.org``, all
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involved machines run Debian 12, your old site’s IP version 4 address is
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``$OLD_IP4``, and your new site’s IP4 address is ``$NEW_IP4``.
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First of all, you should lower the Time To Live (TTL) of your DNS records
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to a value such as 300 (5 minutes).
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Short TTL values allow to change DNS records during the migration more timely.
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During the guide you might get a warning about changed SSH Host keys; in
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this case, just run ``ssh-keygen -R "mail.example.org"`` as recommended.
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1. First, to make the downtime during the migration shorter,
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let's transfer the current state of the mailboxes.
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Login to your old machine (while forwarding your ssh-agent with ``ssh -A``)
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so you can copy directly from the old to the new site with your SSH
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key:
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::
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ssh -A root@$OLD_IP4
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tar c - /home/vmail/mail | ssh root@$NEW_IP4 "tar x -C /"
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This saves us time during the downtime,
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at least the mailboxes are there already.
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They contain user passwords, encrypted push notification tokens,
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messages which might not have been fetched by all devices of the user yet,
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and dovecot indexes which track the state of the mailbox.
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2. Then, from your local machine, install chatmail on the new machine, but don't activate it yet:
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::
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CMDEPLOY_STAGES=install,configure cmdeploy run --ssh-host $NEW_IP4
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The services are disabled for now; we will enable them later.
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We first need to make the new site fully operational.
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3. Now it's getting serious: disable the mail services on the old site.
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::
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cmdeploy run --disable-mail --ssh-host $OLD_IP4
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Your users will start to notice the migration and will not be able to send
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or receive messages until the migration is completed.
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Other relays and mail servers will wait with delivering messages
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until your relay is reachable again.
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4. Now we want to copy ``/home/vmail``, ``/var/lib/acme``,
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``/etc/dkimkeys``, and ``/var/spool/postfix`` to
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the new site. Let's forward the SSH agent again to copy the files directly.
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This time, we copy ``/home/vmail/mail`` with rsync to only copy the recent changes:
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::
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ssh -A root@$OLD_IP4
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tar c - /var/lib/acme /etc/dkimkeys /var/spool/postfix | ssh root@$NEW_IP4 "tar x -C /"
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rsync -azH /home/vmail/mail root@$NEW_IP4:/home/vmail/
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This transfers all addresses, messages which have not been fetched yet, the TLS certificate,
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and DKIM keys (so DKIM DNS record remains valid).
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It also preserves the Postfix mail spool so any messages
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pending delivery will still be delivered.
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5. Now login to the new site and run the following to ensure the ownership is correct
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in case UIDs/GIDs changed:
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::
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ssh root@$NEW_IP4
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chown root: -R /var/lib/acme
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chown opendkim: -R /etc/dkimkeys
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chown vmail: -R /home/vmail/mail
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6. Now, update the DNS entries.
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You only need to change the ``A`` and ``AAAA`` records, for example:
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::
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mail.example.org. IN A $NEW_IP4
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mail.example.org. IN AAAA $NEW_IP6
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7. Finally, you can execute ``CMDEPLOY_STAGES=activate cmdeploy run --ssh-host $NEW_IP4`` to
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turn on chatmail on the new relay. Your users will be able to use the
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chatmail relay as soon as the DNS changes have propagated. Voilà!
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