bundle exec cap production deployで自動デプロイしようとするとMysql2::Error::ConnectionError...

前提・実現したいこと

$ bundle exec cap production deployでデプロイしたい

ここに質問の内容を詳しく書いてください。
railsでアプリケーションを作っています。アプリにEC2を導入しその後DockerとCircleCIを導入しました。
導入した後に自動デプロイするとmysqlエラーになりました。

発生している問題・エラーメッセージ

Mysql2::Error::ConnectionError: Unknown MySQL server host 'db' (2)

該当のソースコード

database.yml

yml
1default: &default
2  adapter: mysql2
3  encoding: utf8
4  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
5  username: root
6  password: password
7  socket: /tmp/mysql.sock
8  host: db
9
10development:
11  <<: *default
12  database: errors_original_app_development
13
14test:
15  <<: *default
16  database: errors_original_app_test
17
18production:
19  <<: *default
20  adapter: mysql2
21  encoding: utf8
22  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
23  username: root
24  password:
25  socket: /tmp/mysql.sock
26  username: root
27  database: errors_original_app_production
28  password: <%= ENV['DATABASE_PASSWORD'] %>
29  socket: /var/lib/mysql/mysql.sock

docker-compose.yml

yml
1version: '3'
2services:
3  db:
4    image: mysql:5.7
5    environment:
6      MYSQL_ROOT_PASSWORD: password
7      MYSQL_DATABASE: root
8    ports:
9      - "4306:3306"
10    volumes:
11      - ./mysql-confd:/etc/mysql/conf.d
12
13
14  web:
15    build: .
16    command: rails s -p 3000 -b '0.0.0.0'
17    volumes:
18      - .:/app_name
19    ports:
20      - "3000:3000"
21    links:
22      - db
23      - chrome
24    stdin_open: true
25    tty: true
26
27  chrome:
28    image: selenium/standalone-chrome:3.141.59-dubnium
29    ports:
30      - 4444:4444

Dockerfile

FROM ruby:2.6.5

FROM ruby:2.6.5

WORKDIR /tmp
RUN apt update && apt install -y lsb-release \ 
    && apt remove -y libmariadb-dev-compat libmariadb-dev

RUN wget https://dev.mysql.com/get/Downloads/MySQL-8.0/mysql-common_8.0.18-1debian10_amd64.deb \
    https://dev.mysql.com/get/Downloads/MySQL-8.0/libmysqlclient21_8.0.18-1debian10_amd64.deb \
    https://dev.mysql.com/get/Downloads/MySQL-8.0/mysql-community-client-core_8.0.18-1debian10_amd64.deb \
    https://dev.mysql.com/get/Downloads/MySQL-8.0/mysql-community-client_8.0.18-1debian10_amd64.deb \
    https://dev.mysql.com/get/Downloads/MySQL-8.0/libmysqlclient-dev_8.0.18-1debian10_amd64.deb

RUN dpkg -i mysql-common_8.0.18-1debian10_amd64.deb \
    libmysqlclient21_8.0.18-1debian10_amd64.deb \
    mysql-community-client-core_8.0.18-1debian10_amd64.deb \
    mysql-community-client_8.0.18-1debian10_amd64.deb \
    libmysqlclient-dev_8.0.18-1debian10_amd64.deb

RUN mkdir /app_name
ENV APP_ROOT /app_name 
WORKDIR $APP_ROOT

ADD ./Gemfile $APP_ROOT/Gemfile
ADD ./Gemfile.lock $APP_ROOT/Gemfile.lock

RUN gem install bundler
RUN bundle install
ADD . $APP_ROOT

.circleci/config.yml

yml
1version: 2
2jobs:
3  build:
4    docker:
5      - image: circleci/ruby:2.6.5-node-browsers
6        environment:
7          RAILS_ENV: test
8          MYSQL_HOST: 127.0.0.1
9          MYSQL_USERNAME: 'root'
10          MYSQL_PASSWORD: ''
11          MYSQL_PORT: 3306
12      - image: circleci/mysql:5.6
13        environment:
14          MYSQL_ALLOW_EMPTY_PASSWORD: true
15          MYSQL_ROOT_PASSWORD: ''
16          MYSQL_DATABASE: circle_ci_test-test
17
18    working_directory: ~/circle-ci-test
19
20    steps:
21      - checkout
22