docker-compose: accessing postgres' shell (psql)

Let's start with a minimal docker-compose.yml file for reference:

version: "3"

services:
  postgres:
    image: postgres:9.5

You bring your services up with docker-compose up.

Let's assume you have a database you want to connect to called test.

Answer: docker-compose run --rm postgres psql -h YOUR_SERVICE -U YOUR_USER -d YOUR_DATABASE

The --rm option removes the container after exit, so you don't create unnecessary duplicate containers just for accessing the database.

In our example, this would be docker-compose run --rm postgres psql -h postgres -U postgres -d test

Alternatively, you could use psql's connection string: docker compose run --rm postgres psql -d postgres://YOUR_USER@YOUR_SERVICE/YOUR_DATABASE

Things have changed a bit since the question was originally asked.

Here's how you can access PostgreSQL's shell (psql) using docker-compose today:

1. Use a docker-compose.yml version '2' config file
2. Use 'depends_on' rather than 'links' (new to version '2')
3. Break up your containers using 'services'

docker-compoose.yml

version: '2'
services:      
   postgresdb:
     build: utils/sql/
     ports:
       - "5432"
     environment:
       - DEBUG=true
   main:
     build: .
     volumes:
       - .:/code
     depends_on:
       - postgresdb
     environment:
       - DEBUG=true

In your docker engine shell ...

1. Find the container id (or container name) from the docker ps command
2. Use that id to open a shell prompt
3. Switch user to the postgres user account
4. Run psql

See example below:

                        ##         .
                  ## ## ##        ==
               ## ## ## ## ##    ===
           /"""""""""""""""""\___/ ===
      ~~~ {~~ ~~~~ ~~~ ~~~~ ~~~ ~ /  ===- ~~~
           \______ o           __/
             \    \         __/
              \____\_______/
 _                 _   ____     _            _
| |__   ___   ___ | |_|___ \ __| | ___   ___| | _____ _ __
| '_ \ / _ \ / _ \| __| __) / _` |/ _ \ / __| |/ / _ \ '__|
| |_) | (_) | (_) | |_ / __/ (_| | (_) | (__|   <  __/ |
|_.__/ \___/ \___/ \__|_____\__,_|\___/ \___|_|\_\___|_|
Boot2Docker version 1.11.2, build HEAD : a6645c3 - Wed Jun  1 22:59:51 UTC 2016
Docker version 1.11.2, build b9f10c9
docker@default:~$ docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                    NAMES
b563764171e2        poc_web             "bundle exec rails s "   43 minutes ago      Up 43 minutes       0.0.0.0:3000->3000/tcp   poc_web_1
c6e480b0f26a        postgres            "/docker-entrypoint.s"   49 minutes ago      Up 49 minutes       0.0.0.0:5432->5432/tcp   poc_db_1
docker@default:~$ docker exec -it c6e480b0f26a sh
# su - postgres
No directory, logging in with HOME=/
$ psql
psql (9.5.3)
Type "help" for help.

postgres=#

Notes:

1. docker-compose up will start services in dependency order

2. If you want to stand up a postgres container using the official image, you docker-compose.yml might look more like the following:

   version: '2'
   services:      
     db:
       image: postgres
       ports:
         - "5432:5432"
   . . .
   

References

https://docs.docker.com/compose/compose-file/