GitLab CI for Rails App Using Postgres and Elasticsearch (searchkick gem) - ruby-on-rails

Question

How does one go about configuring a .gitlab-ci.yml file for a Rails app that depends on PosgreSQL and Elasticsearch via the searchkick gem to run my tests when I push it to GitLab?

Answer 1

I wanted to post this question, as it took me far too long to find the answer and don't want others to feel my pain. The below example not only builds my application, but also runs all my specs.
Setup
Rails 5+
PostreSQL 9.6
Rspec gem
Searchkick gem (handles Elasticsearch queries and configuration)
Configuration
Add the following files to your Rails app with the configurations listed.
config/gitlab-database.yml
test:
adapter: postgresql
encoding: unicode
pool: 5
timeout: 5000
host: postgres
database: test_db
user: runner
password: ""
.gitlab-ci.yml
image: ruby:2.4.1
services:
- postgres:latest
- elasticsearch:latest
variables:
POSTGRES_DB: test_db
POSTGRES_USER: runner
POSTGRES_PASSWORD: ""
ELASTICSEARCH_URL: "http://elasticsearch:9200"
stages:
- test
before_script:
- bundle install --without postgres production --jobs $(nproc) "${FLAGS[#]}"
- cp config/gitlab-ci/gitlab-database.yml config/database.yml
- RAILS_ENV=test bundle exec rails db:create db:schema:load
test:
stage: test
script:
- bundle exec rspec
And that's it! You're now configured to auto-run your specs on gitlab for each push.
Further Explaination
Let's start with PostgreSQL. When we start our new runner, the application we're copying in won't know how to properly connect to Postgres. Thus we create a new database.yml file, which we prefixed with gitlab- so it doesn't conflict with our actual configuration, and copy that file into runner's config directory. The cp command not only copy's the file, but will replace the file if it currently exists.
The items we're connecting to via GitLab are database:, user:, and password:. We do this by specifying those same names within our environment variables, ensuring everything connects properly.
Okay, connecting to PostgreSQL is well explained and documented on GitLab's website. So how did I get Elasticsearch working, which isn't explained very well anywhere?
The magic happens again in variables. We needed to set the ELASTICSEARCH_URL environmental variable, made available to us through the Searchkick gem, as Elasticsearch looks for http://localhost:9200 by default. But since we're using Elasticsearch through a service, we need to explicitly tell it to not use the default and use our service's hostname. So we then replaced http://localhost:9200 with http://elasticsearch:9200, which does map properly to our service.