Dokker + Postgres, avoiding "PG::ConnectionBad: could not connect to server: Connection refused"

gistfile1.txt

# Create database, save Url for later use, let's call it <saved_url>
dokku postgresql:create <database>

# Link
dokku postgresql:link <app_name> <database>

# Check db url
dokku config <app_name> | grep DATABASE_URL

# if saved url is not equals to the last displayed, then:
dokku config:set <app_name> DATABASE_URL=<saved_url>

# Migrate
dokku run <app_name> bundle exec rake db:migrate