CircleCI with Ruby 2.5, Rails 5.2, Yarn, Webpacker, Sass, PostgreSQL, Redis, ElasticSearch full example.

config.yml

version: 2
jobs:
  build:
    docker:
      - image: circleci/ruby:2.5.3-node-browsers
        environment:
          RAILS_ENV: test
          DATABASE_URL: postgres://postgres@127.0.0.1:5432/rails-test
      - image: circleci/postgres:9.6
        environment:
          POSTGRES_USER: "postgres"
          POSTGRES_PASSWORD: ""
          POSTGRES_DB: "rails-test"
      - image: circleci/redis:4-alpine3.8
      - image: docker.elastic.co/elasticsearch/elasticsearch:6.2.2
        environment:
          - xpack.security.enabled: false

    working_directory: ~/repo

    steps:
      - checkout

      - run:
          name: Dockerize v0.6.0
          command: |
            wget https://github.com/jwilder/dockerize/releases/download/v0.6.0/dockerize-linux-amd64-v0.6.0.tar.gz
            sudo rm -rf /usr/local/bin/dockerize
            sudo tar -C /usr/local/bin -xzvf dockerize-linux-amd64-v0.6.0.tar.gz
            rm dockerize-linux-amd64-v0.6.0.tar.gz
      - run:
          name: Wait for PG
          command: dockerize -wait tcp://localhost:5432 -timeout 1m

      - run:
          name: Wait for Redis
          command: |
            dockerize -wait tcp://localhost:6379 -timeout 1m
      - run:
          name: Wait for ElasticSearch
          command: |
            dockerize -wait tcp://localhost:9200 -timeout 1m
      # Download and cache dependencies
      - restore_cache:
          keys:
          - v1-dependencies-{{ checksum "Gemfile.lock" }}-{{ checksum "yarn.lock" }}
          # fallback to using the latest cache if no exact match is found
          - v1-dependencies-

      - run:
          name: install dependencies
          command: |
            curl -o- -L https://yarnpkg.com/install.sh | bash
            yarn global add sass
            bundle install --jobs=4 --retry=3 --path vendor/bundle
            yarn
      - save_cache:
          paths:
            - ./vendor/bundle
            - ~/.cache/yarn
          key: v1-dependencies-{{ checksum "Gemfile.lock" }}-{{ checksum "yarn.lock" }}

      # Database setup
      - run: bundle exec rake db:create
      - run: bundle exec rake db:schema:load

      - run:
          name: Rubocop
          command: bundle exec rubocop

      - run:
          name: Rails Test
          command: bundle exec rails test