RailsアプリをCircleCIでデプロイしたいが、master.keyが設定できない

環境
RubyonRails 5.2.2
carrierwave

CircleCIでECSへデプロイするdockerイメージのビルドの中でアセットのプリコンパイルを行った際、CircleCIのEnvironment Variablesに入っているRAILS_MASTER_KEYが参照されずプリコンパイルがエラーになる。

アセットはAWSのS3に配置するためS3のアクセスキーをcredential.yml.encに記述しておりそれを参照したい。

エラー文

Step 17/19 : RUN RAILS_ENV=production bundle exec rake assets:precompile
 ---> Running in af27c5633055
rake aborted!
NoMethodError: undefined method `[]' for nil:NilClass
/usr/src/eStreak/config/initializers/carrierwave.rb:12:in `block in <main>'
/usr/local/bundle/gems/carrierwave-1.3.1/lib/carrierwave/uploader/configuration.rb:161:in `configure'
/usr/local/bundle/gems/carrierwave-1.3.1/lib/carrierwave.rb:14:in `configure'
/usr/src/eStreak/config/initializers/carrierwave.rb:5:in `<main>'

NoMethodError: undefined method `[]' for nil:NilClass

とされているがcredentials.yml.encにはしっかりと記述しており、ローカルで試したところmaster.keyが配置されていない場合にこのエラーが出るのでmaster.keyが参照されてないのではと疑っている。

以下は本番環境のdockerfileと.circleci/config.ymlです。

Dockerfile

FROM ruby:2.4.0

ENV APP_ROOT /usr/src/eStreak

WORKDIR $APP_ROOT

RUN printf "deb http://archive.debian.org/debian/ jessie main\ndeb-src http://archive.debian.org/debian/ jessie main\ndeb http://security.debian.org jessie/updates main\ndeb-src http://security.debian.org jessie/updates main" > /etc/apt/sources.list
RUN apt-get update
RUN apt-get install -y \
    nodejs \
    npm \
    --no-install-recommends && \
    rm -rf /var/lib/apt/lists/*

COPY Gemfile $APP_ROOT
COPY Gemfile.lock $APP_ROOT

RUN \
  echo 'gem: --no-document' >> ~/.gemrc && \
  cp ~/.gemrc /etc/gemrc && \
  chmod uog+r /etc/gemrc && \
  bundle config --global build.nokogiri --use-system-libraries && \
  bundle config --global jobs 4 && \
  bundle install && \
  rm -rf ~/.gem

COPY . $APP_ROOT

EXPOSE  3000

RUN npm install
RUN npm install yarn -g
RUN npm install n -g

RUN n 10.15.3

RUN ln -s /usr/bin/nodejs /usr/bin/node

RUN RAILS_ENV=production bundle exec rake assets:precompile
RUN rm -f tmp/pids/server.pid
CMD ["bundle", "exec", "rails", "s", "puma", "-b", "0.0.0.0", "-p", "3000", "-e", "production"]

.circleci/config.yml

version: 2.1
jobs:
  checkout_code:
    docker:
      - image: stks56/estreak_pro:latest
    working_directory: ~/eStreak
    steps:
      - checkout
      - save_cache:
          key: v1-repo-{{ .Environment.CIRCLE_SHA1 }}
          paths:
            - ~/eStreak
  test:
    docker:
      - image: stks56/estreak_pro:latest
        environment:
          RAILS_ENV: test
          MYSQL_HOST: 127.0.0.1
          MYSQL_USERNAME: 'root'
          MYSQL_PASSWORD: ''
          MYSQL_PORT: 3306
      - image: mysql:5.7
        environment:
          MYSQL_DATABASE: eStreak_test
          MYSQL_ALLOW_EMPTY_PASSWORD: true
          MYSQL_ROOT_HOST: '%'
    working_directory: ~/eStreak
    steps:
      - checkout
      - restore_cache:
          key: v1-repo-{{ .Environment.CIRCLE_SHA1 }}
      - restore_cache:
          keys:
          - v1-dependencies-{{ checksum "Gemfile.lock" }}
          - v1-dependencies-
      - run:
          name: install dependencies
          command: |
            bundle install --jobs=4 --retry=3 --path vendor/bundle
      - save_cache:
          paths:
          - ./vendor/bundle
          key: v1-dependencies-{{ checksum "Gemfile.lock" }}
      # Database setup
      - run: rm ./config/database.yml
      - run: mv ./config/database.yml.ci ./config/database.yml
      - run:
          name: Prepare db
          command: |
            bundle exec rake db:create db:schema:load --trace
      # run tests!
      - run:
          name: Run rspec
          command: |
            mkdir /tmp/test-results
            TEST_FILES="$(circleci tests glob "spec/**/*_spec.rb" | circleci tests split --split-by=timings)"
            bundle exec rspec --format progress --color --format documentation
      # collect reports
      - store_test_results:
          path: /tmp/test-results
      - store_artifacts:
          path: /tmp/test-results
          destination: test-results

  deploy:
    docker:
      - image: circleci/python
    steps:
      - checkout
      - setup_remote_docker
      - run:
          name: install aws
          command: |
            sudo pip install awscli
            aws --version
      - run:
          name: Install ecs-deploy
          command: |
            curl https://raw.githubusercontent.com/silinternational/ecs-deploy/master/ecs-deploy | sudo tee -a /usr/bin/ecs-deploy
            sudo chmod +x /usr/bin/ecs-deploy
      - run:
          name: Install jq
          command: sudo apt-get install -y jq
      - run:
          name: "Log in to AWS ECR"
          command: eval $(aws ecr get-login --no-include-email --region ap-northeast-1)
      - run:
          name: "Build & Push Docker Image"
          command: |
            docker build -t $AWS_ACCOUNT_ID.dkr.ecr.ap-northeast-1.amazonaws.com/estreak_app_repo:latest -t $AWS_ACCOUNT_ID.dkr.ecr.ap-northeast-1.amazonaws.com/estreak_app_repo:$CIRCLE_SHA1 -f Dockerfile_PRO .
            docker push $AWS_ACCOUNT_ID.dkr.ecr.ap-northeast-1.amazonaws.com/estreak_app_repo:$CIRCLE_SHA1

      - run:
          name: "DB Migrate"
          command: |
            aws ecs run-task \
              --region ap-northeast-1 \
              --cluster eStreak-cluster \
              --task-definition estreak_app_task \
              --overrides file://ecs/run_task_db_migrate.json
      - run:
          name: "Sevice deploy"
          environment:
          command: |
            ecs-deploy -c eStreak-cluster -n eStreak_app_service \
              -r ap-northeast-1 -t 240 \
              -i $AWS_ACCOUNT_ID.dkr.ecr.ap-northeast-1.amazonaws.com/estreak_app_repo:$CIRCLE_SHA1

workflows:
  version: 2.1
  test_and_deploy:
    jobs:
      - checkout_code
      - test:
          requires:
            - checkout_code
      - deploy:
          requires:
            - test
          filters:
            branches:
              only: master