How to run redmine with a postgresql database using docker compose - docker

Question

Using the official redmine docker guide it is possible to start a redmine server connected to a postgresql database. I used the following commands:
docker run -d --name redmine_db -p 6543:5432 -e POSTGRES_PASSWORD=secret -e POSTGRES_USER=redmine postgres:9.5.1
docker run -d --name redmine_web -p 3001:3000 --link redmine_db:postgres redmine:3.2.3
But I have difficulties to run the same configuration with docker compose. Here is the first docker-compose.yml file I used:
version: '2'
services:
webserver:
image: redmine:3.2.3
ports:
- "3001:3000"
links:
- database:postgres
database:
image: postgres:9.5.1
ports:
- "6543:5432"
environment:
- POSTGRES_PASSWORD="secret"
- POSTGRES_USER="redmine"
With docker compose the redmine server starts correctly but it ignores the postgres database container and uses the internal SQLite database instead.
I've also tried with the following environments in the webserver configuration:
environment:
- POSTGRES_PORT_5432_TCP="5432"
- POSTGRES_ENV_POSTGRES_USER="redmine"
- POSTGRES_ENV_POSTGRES_PASSWORD="secret"
But without success. This time the redmine container does not start at all and displays the following error message:
[!] There was an error parsing `Gemfile`: (<unknown>): did not find expected key while parsing a block mapping at line 2 column 3. Bundler cannot continue.
# from /usr/src/redmine/Gemfile:64
# -------------------------------------------
# if File.exist?(database_file)
> database_config = YAML::load(ERB.new(IO.read(database_file)).result)
# adapters = database_config.values.map {|c| c['adapter']}.compact.uniq
# -------------------------------------------

Answer 1

From docker-compose version 2 docs:
links with environment variables: As documented in the environment
variables reference, environment variables created by links have been
deprecated for some time. In the new Docker network system, they have
been removed. You should either connect directly to the appropriate
hostname or set the relevant environment variable yourself, using the
link hostname:
web:
links:
- db
environment:
- DB_PORT=tcp://db:5432
In docker-compose v. 2 you should use networks instead. All services in docker-compose in one common network by default. In your config your webserver container can resolve database by database host without any links.