Last Updated: September 17, 2023
· naohiro

Heroku postgres create follower db and promote follower to master from slave

I needed to migrate heroku postgres between 2 different heroku applications. One of them has heroku postgres add-on, but the other was connecting to first application's postgres.
However, I wanted to delete first application, so here is how I migrated heroku postgress add-on to another application.

NOTE: you cannot use follower db with hobby plan

  1. Create new postgres on second app which follows original db

    heroku addons:create heroku-postgresql:standard-0 --follow postgresql-test-xxxx -a second_app

    you can check add-on name with

    heroku pg:info -a first_app
  2. Check how much new db catch up original

    heroku pg:info -a second_app

    This returns

    Behind By:   125 commits

    Once behind by is 0 commits, you are ready to promote!!

  3. Turn on maintenance mode to avoid database update(this cause downtime, but should be less than 1 min...)

    heroku maintenance:on -a first_app
    heroku maintenance:on -a second_app
  4. Unfollow the original postgres

    heroku pg:unfollow HEROKU_POSTGRESQL_COLOR_URL -a second_app

    (this url is new postgres url. you can get with heroku config -a second_app)

  5. Promote new postgres

    heroku pg:promote HEROKU_POSTGRESQL_COLOR -a second_app

    This update config DATABESE_URL with new postgres URL

  6. Turn off maintenance mode

    heroku maintenance:off -a first_app
    heroku maintenance:off -a second_app