Pipeline: Something is overwriting my database adapter configs

[Mike Han]

I have a rails 5 repository that's trying to run CI with pipeline. It's running a custom image using the following Dockerfile

# Use an official Ruby runtime as a parent image
FROM ruby:2.3.1-slim

MAINTAINER mmhan

# Install curl
RUN apt-get update && apt-get install -y curl

# Update packagelist
RUN curl -sL https://deb.nodesource.com/setup_10.x | bash -
RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add -
RUN echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list

# Install further requirements to run ruby on rails
RUN apt-get update && apt-get install -y \
 build-essential \
 mysql-client \
 libmysqlclient-dev \
 nodejs \
 yarn \
 vim

# Configure the main working directory
RUN mkdir -p /app
WORKDIR /app

The steps in pipelines.yml are as followed:

 - step:
    caches:
      - bundler
      - yarn
    services:
      - mysql
    script:
      # set up database
      - export DATABASE_URL=mysql://test_user:test_user_password@localhost/mmcdb_ci_production
      - cp ./config/database.ci.yml ./config/database.yml

      # set up bundle
      - bundle install --deployment --path vendor/bundle

      # run tests
      - pwd
      - cat config/database.yml
      - bundle exec rails runner 'pp Rails.configuration.database_configuration'

The `cat` command always outputs the correct configuration with `mysql2` adapter. However, when `config/environment.rb` is ran it complains that it cannot find `mysql` adapter. 

By catching the exception in environment.rb, I can see the output of the configuration being over-written:

puts 'Rails environment: ' + Rails.env.to_s
begin
 # Load the Rails application.
 require_relative 'application'

 # Initialize the Rails application.
 Rails.application.initialize!
rescue LoadError
 pp Rails.configuration.database_configuration #output 1
 pp ActiveRecord::Base.configurations #output 2
end

The output 1 is always correct as followed:

{"default"=>{"adapter"=>"mysql2", "encoding"=>"utf8", "host"=>"localhost"},
 "development"=>
 {"adapter"=>"mysql2",
 "encoding"=>"utf8",
 "host"=>"localhost",
 "database"=>"mmcdb_ci_development"},
 "test"=>
 {"adapter"=>"mysql2",
 "encoding"=>"utf8",
 "host"=>"localhost",
 "database"=>"mmcdb_ci_test",
 "username"=>"test_user",
 "password"=>"test_user_password"},
 "production"=>
 {"adapter"=>"mysql2",
 "encoding"=>"utf8",
 "host"=>"localhost",
 "database"=>"mmcdb_ci_production"}}

And the output 2 is the one that's being overwritten:

{"default"=>{"adapter"=>"mysql2", "encoding"=>"utf8", "host"=>"localhost"},
 "development"=>
 {"adapter"=>"mysql2",
 "encoding"=>"utf8",
 "host"=>"localhost",
 "database"=>"mmcdb_ci_development"},
 "test"=>
 {"adapter"=>"mysql",
 "encoding"=>"utf8",
 "host"=>"localhost",
 "database"=>"mmcdb_ci_production",
 "username"=>"test_user",
 "password"=>"test_user_password"},
 "production"=>
 {"adapter"=>"mysql2",
 "encoding"=>"utf8",
 "host"=>"localhost",
 "database"=>"mmcdb_ci_production"}}

What's going on here? Was there something in the pipeline that's doing some kind of automagic configurations for me that I should take note of? Or is it all rails?

[Mike Han]

Atlassian team has helped us answer the question via a support ticket.

The environment variable `DATABASE_URL` is the one that's making rails look for `sql` adapter. If I removed it, it works as expected.