i have questions about docker-compose

Question

postgres:

image: healthcheck/postgres:alpine
environment:
  POSTGRES_USER: postgres

• What is the default user of postgresql?
• How does hardcoding the postgres user improve security?
• What special rights does the postgres user have?
• What is the upside and downside of using an unprivileged user in this scenario?
• Is it necessary in our scenario to have an unprivileged user?

Answer 1

I searched for the healthcheck/postgres:alpine and I found the following repository with the Dockerfile:

https://github.com/docker-library/healthcheck/blob/master/postgres/Dockerfile.alpine

Assuming this is the correct repo for your docker image, the dockerfile specifies:

FROM postgres

COPY docker-healthcheck /usr/local/bin/

HEALTHCHECK CMD ["docker-healthcheck"]

So it extends the postgres docker image which is documented here:

https://hub.docker.com/_/postgres

Specifically for the password they mention the following:

POSTGRES_PASSWORD This environment variable is recommended for you to use the PostgreSQL image. This environment variable sets the superuser password for PostgreSQL. The default superuser is defined by the POSTGRES_USER environment variable.

Note 1: The PostgreSQL image sets up trust authentication locally so you may notice a password is not required when connecting from localhost (inside the same container). However, a password will be required if connecting from a different host/container...

Read the whole documentation at the image homepage.