EDIT - since Jul 23, 2015

The official postgres docker image will run .sql scripts found in the /docker-entrypoint-initdb.d/ folder.

So all you need is to create the following sql script:

init.sql

CREATE USER docker;
CREATE DATABASE docker;
GRANT ALL PRIVILEGES ON DATABASE docker TO docker;

and add it in your Dockerfile:

Dockerfile

FROM library/postgres
COPY init.sql /docker-entrypoint-initdb.d/

But since July 8th, 2015, if all you need is to create a user and database, it is easier to just make use to the POSTGRES_USER, POSTGRES_PASSWORD and POSTGRES_DB environment variables:

docker run -e POSTGRES_USER=docker -e POSTGRES_PASSWORD=docker -e POSTGRES_DB=docker library/postgres

or with a Dockerfile:

FROM library/postgres
ENV POSTGRES_USER docker
ENV POSTGRES_PASSWORD docker
ENV POSTGRES_DB docker

for images older than Jul 23, 2015

From the documentation of the postgres Docker image, it is said that

[...] it will source any *.sh script found in that directory [/docker-entrypoint-initdb.d] to do further initialization before starting the service

What's important here is "before starting the service". This means your script make_db.sh will be executed before the postgres service would be started, hence the error message "could not connect to database postgres".

After that there is another useful piece of information:

If you need to execute SQL commands as part of your initialization, the use of Postgres single user mode is highly recommended.

Agreed this can be a bit mysterious at the first look. What it says is that your initialization script should start the postgres service in single mode before doing its actions. So you could change your make_db.ksh script as follows and it should get you closer to what you want:

NOTE, this has changed recently in the following commit. This will work with the latest change:

export PGUSER=postgres
psql <<- EOSQL
    CREATE USER docker;
    CREATE DATABASE docker;
    GRANT ALL PRIVILEGES ON DATABASE docker TO docker;
EOSQL

Previously, the use of --single mode was required:

gosu postgres postgres --single <<- EOSQL
    CREATE USER docker;
    CREATE DATABASE docker;
    GRANT ALL PRIVILEGES ON DATABASE docker TO docker;
EOSQL

If, when you start your Docker Compose, you're getting:

PostgreSQL Database directory appears to contain a database; Skipping initialization

you need to proactively remove the volumes which were set up to store the database.

The command docker-compose down doesn't do this automatically.

You can request removal of volumes like this:

docker-compose down --volumes

Be warned that this will delete any data you had in any database before. You can't get this data back if you remove the volume which contained it!

If 3&4 are designed to "reinit" the postgres from the bind mounted init data I think all you need to do is remove the service.

docker-compose stop
docker-compose rm postgres  # should remove the attached volumes
docker-compose up -d # should recreate the volume and run the initdb script

EDIT:

Personally I also feel like "just blowing it away" seems a little hasty, if there are any database writes you will lose them. Before you stop you could easily have made a backup.

docker-compose exec {servicename} pg_dumpall -c -U postgres > dump_`date +%d-%m-%Y"_"%H_%M_%S`.sql

And then go ahead and then stop/rm the service since you have a backup.

EDIT2:

You may need docker-compose rm -v postgres if you didn't explicitly declare the volumes. The flag tells it to also remove the anonymous volumes associated with the image.