Docker-compose rails postgres - ruby-on-rails

Question

I've been following this tutorial to 'dockerize' my rails application and have hit a snag with connecting to the db after some searching around, no solutions seem to work. I've also tried the default user 'postgres' and no password, but still no luck. My error indicates that my password is incorrect, but everything I try doesn't change the error:
web_1 | I, [2017-06-02T00:58:29.217947 #7] INFO -- : listening on addr=0.0.0.0:3000 fd=13
postgres_1 | FATAL: password authentication failed for user "web"
postgres_1 | DETAIL: Connection matched pg_hba.conf line 95: "host all all 0.0.0.0/0 md5"
web_1 | E, [2017-06-02T00:58:29.230868 #7] ERROR -- : FATAL: password authentication failed for user "web"
Here's what I have:
.env
LISTEN_ON=0.0.0.0:3000
DATABASE_URL=postgresql://web:mypassword#postgres:5432/web?encoding=utf8&pool=5&timeout=5000
Dockerfile
FROM ruby:2.3.4
RUN apt-get update && apt-get install -qq -y build-essential nodejs libpq-dev postgresql-client-9.4 --fix-missing --no-install-recommends
ENV INSTALL_PATH /web
RUN mkdir -p $INSTALL_PATH
WORKDIR $INSTALL_PATH
COPY Gemfile Gemfile
COPY Gemfile.lock Gemfile.lock
RUN bundle install
COPY . .
# precompile assets using dummy data
RUN bundle exec rake RAILS_ENV=production DATABASE_URL=postgresql://user:pass#127.0.0.1/dbname SECRET_TOKEN=pickasecuretoken assets:precompile
VOLUME ["$INSTALL_PATH/public"]
VOLUME /postgres
CMD RAILS_ENV=development bundle exec unicorn -c config/unicorn.rb
docker-compose.yml
postgres:
image: postgres:9.4.5
environment:
POSTGRES_USER: web
POSTGRES_PASSWORD: mypassword
ports:
- "5432:5432"
volumes:
- postgres:/var/lib/postgresql/data
web:
build: .
links:
- postgres
volumes:
- .:/web
ports:
- "3000:3000"
env_file:
- .env
config/database.yml
default: &default
adapter: postgresql
encoding: unicode
pool: 5
development:
<<: *default
url: <%= ENV['DATABASE_URL'] %>
The line in database.yml grabs the DATABASE_URL environment variable that is stored in the container from the .env file.

Answer 1

I spent the better part of a day fiddling with this. What finally worked for me was to fall back to the Postgres defaults.
docker-compose.yml
postgres:
image: postgres:9.4.5
ports:
- "5432:5432"
volumes:
- postgres:/var/lib/postgresql/data
.env
DATABASE_URL=postgresql://web:#postgres:5432/web?encoding=utf8&pool=5&timeout=5000
In the DATABASE_URL, keeping the password separator in the url but leaving the password blank finally made it work.