Migrating a Dokku application to a new server

Assuming a few things:

the original server is still running, and that the new server cannot be bootstrapped from an image or backup of the old server (for example, they are with different hosts)
Dokku has been installed on the new server and is accessible using the dokku user (See https://dokku.com)
We have an SSH config entry for both old and new servers in ~/.ssh/config:

host new_server
  RequestTTY yes
  Hostname 55.190.140.231
  User dokku
  IdentityFile ~/.ssh/id_rsa

Host old_server
  RequestTTY yes
  Hostname 55.78.183.109
  User dokku
  IdentityFile ~/.ssh/id_rsa

Create new app

ssh new_server apps:create icepop_app

Fetch env vars for original

ssh old_server config:show icepop_app

Set important keys (not DOKKU_*)

ssh new_server config:set icepop_app RAILS_MASTER_KEY=VALUE EMAIL_API_KEY=VALUE MAP_API_KEY=VALUE

Add new git remote repo based on the current one

git remote -v

git remote add new_server dokku@new_server:icepop_app

Create new DB

ssh new_server postgres:create icepop_app_production

Link DB to the new app

ssh new_server postgres:link icepop_app_production icepop_app

Dump the data from the old DB You might want to do this at a slow time to minimise lost updates, or introduce the maintenance page.

ssh old_server postgres:export icepop_app-production > ~/Downloads/sql/icepop_app_production.dump

Import the dump

ssh new_server postgres:import icepop_app_production < ~/Downloads/sql/icepop_app_production.dump

Deploy the project

git push new_server deploy:main

Add domains to the app

ssh new_server domains:add icepop_app www.icepop_app.com icepop_app.com

Configure SSL certificate(s) via letsencrypt

ssh new_server letsencrypt:set icepop_app email james@icepop_app.com

Check where the DNS is configured and move the A records to point to the new server using the registrar’s UI whois will give you a clue which registrar you used if you’re anything like me and have three in use.

whois icepop_app.com

Request SSL certificates

ssh new_server letsencrypt:enable icepop_app

Tail the logs to ensure traffic is flowing as expected

ssh new_server logs -t icepop_app

Connect to the Rails console to check changes are reflected in the browser

ssh new_server run icepop_app "bundle exec rails console -e production"

All being well, your app is migrated (remember to check for any local file uploads etc) and the old server can be decomissioned.