There is an official postgresql plugin for dokku hosted in the dokku org: https://github.com/dokku/dokku-postgres . I would recommend new users look there first. I will still maintain issues and pull requests here, but encourage users to consider migrating to the official plugin as it will get better support.
Project: https://github.com/progrium/dokku
cd /var/lib/dokku/plugins
git clone https://github.com/jeffutter/dokku-postgresql-plugin postgresql
dokku plugins-install
$ dokku help
postgresql:console <app> Launch a postgresql console for a given app
postgresql:create <app> Create a PostgreSQL database
postgresql:delete <app> Delete specified PostgreSQL database
postgresql:list List all databases
postgresql:start Start the PostgreSQL docker container if it isn't running
postgresql:status Shows status of PostgreSQL
postgresql:stop Stop the PostgreSQL docker container
Start PostgreSQL:
$ dokku postgresql:start # Server side
..or..
$ ssh dokku@server postgresql:start # Client side
Example Output:
9f3d9d19248c110fce9f8489482adafd2172834a0f1d2db9f0140141927501b9
Create a new DB (app with same name has to exist):
$ dokku postgresql:create foo # Server side
..or..
$ ssh dokku@server postgresql:create foo # Client side
Example Output:
CREATE ROLE
CREATE DATABASE
GRANT
-----> Creating /home/dokku/foo/ENV
-----> Setting config vars and restarting foo
DATABASE_URL: postgres://foo:ultrastrongpassword@172.17.0.28:5432/foo
-----> Releasing foo ...
-----> Release complete!
-----> Deploying foo ...
-----> Deploy complete!