Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2 "No such file or directorエラー

Question

お世話になっております。
現在、LuggageMGTというアプリ作成しています。

勉強で、Docker環境でcircleCIを使用しております。

解決したいこと、エラー

ローカルのターミナルにて、docker-compose upをすると、

Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2 "No such file or directory")

と出てしまいます。

#実行したこと
/tmp/mysql.sockが存在するか下記コマンドで確認しました

% mysql_config --socket
/tmp/mysql.sock

下記コマンドでMySQLを再起動させました。

% mysql.server restart
Shutting down MySQL
.. SUCCESS! 
Starting MySQL
.. SUCCESS! 

きちんとファイルは存在するのに、

(2 "No such file or directory")

と出る理由も分かりません。

下記に該当してそうなファイルを記述致します。
まだまだ知識が甘く、変なところもあるかもしれないです。よろしくお願い致します。

database.yml

# MySQL. Versions 5.1.10 and up are supported.
#
# Install the MySQL driver
#   gem install mysql2
#
# Ensure the MySQL gem is defined in your Gemfile
#   gem 'mysql2'
#
# And be sure to use new-style password hashing:
#   https://dev.mysql.com/doc/refman/5.7/en/password-hashing.html
#
default: &default
  adapter: mysql2
  encoding: utf8
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  username: root
  password: password
  host: localhost
  socket: /tmp/mysql.sock

development:
  <<: *default
  database: LuggageMGT_development

# Warning: The database defined as "test" will be erased and
# re-generated from your development database when you run "rake".
# Do not set this db to the same as development or production.
test:
  <<: *default
  database: LuggageMGT_test

# As with config/secrets.yml, you never want to store sensitive information,
# like your database password, in your source code. If your source code is
# ever seen by anyone, they now have access to your database.
#
# Instead, provide the password as a unix environment variable when you boot
# the app. Read http://guides.rubyonrails.org/configuring.html#configuring-a-database
# for a full rundown on how to provide these environment variables in a
# production deployment.
#
# On Heroku and other platform providers, you may have a full connection URL
# available as an environment variable. For example:
#
#   DATABASE_URL="mysql2://myuser:mypass@localhost/somedatabase"
#
# You can use this database configuration with:
#
#   production:
#     url: <%= ENV['DATABASE_URL'] %>
#
production:
  <<: *default
  database: LuggageMGT_production
  username: root
  password: <%= ENV['DATABASE_PASSWORD'] %>
  socket: /tmp/mysql.sock

docker-compose.yml

version: '3'

services:
  web:
    build: .
    ports:
      - "3000:3000"
    tty: true
    command: /bin/sh -c "rm -f tmp/pids/server.pid && bundle exec rails s -p 3000 -b '0.0.0.0'"
    volumes:
      - .:/app_name
    depends_on:
      - db
      
  db:
    image: mysql:5.6.47
    environment:
      MYSQL_ROOT_PASSWORD: password
      MYSQL_DATABASE: root
    ports:
      - "3306:3306"
    volumes:
      - ./tmp/db:/var/lib/mysql/data
volumes:
  bundle:
  mysql_data:

dockerfile

FROM ruby:2.5.3
RUN apt-get update -qq && \
    apt-get install -y build-essential \ 
                       libpq-dev \        
                       nodejs           

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 bundle install
ADD . $APP_ROOT

circleci/config.yml

version: 2.1
orbs:
  ruby: circleci/ruby@0.1.2 

jobs:
  build:
    docker:
      - image: circleci/ruby:2.5.3-stretch-node
      - image: circleci/mysql:5.6.47
        environment:
          MYSQL_ROOT_PASSWORD: "password"
          MYSQL_ROOT_HOST: "%"
    working_directory: ~/LuggageMTG

    executor: ruby/default
    steps:
      - checkout
      - run:
          name: Which bundler?
          command: bundle -v
      - ruby/bundle-install

追記です。
database.ymlです。

# MySQL. Versions 5.1.10 and up are supported.
#
# Install the MySQL driver
#   gem install mysql2
#
# Ensure the MySQL gem is defined in your Gemfile
#   gem 'mysql2'
#
# And be sure to use new-style password hashing:
#   https://dev.mysql.com/doc/refman/5.7/en/password-hashing.html
#
default: &default
  adapter: mysql2
  encoding: utf8
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  username: root
  password: password
  host: localhost

development:
  <<: *default
  database: LuggageMGT_development

# Warning: The database defined as "test" will be erased and
# re-generated from your development database when you run "rake".
# Do not set this db to the same as development or production.
test:
  <<: *default
  database: LuggageMGT_test

# As with config/secrets.yml, you never want to store sensitive information,
# like your database password, in your source code. If your source code is
# ever seen by anyone, they now have access to your database.
#
# Instead, provide the password as a unix environment variable when you boot
# the app. Read http://guides.rubyonrails.org/configuring.html#configuring-a-database
# for a full rundown on how to provide these environment variables in a
# production deployment.
#
# On Heroku and other platform providers, you may have a full connection URL
# available as an environment variable. For example:
#
#   DATABASE_URL="mysql2://myuser:mypass@localhost/somedatabase"
#
# You can use this database configuration with:
#
#   production:
#     url: <%= ENV['DATABASE_URL'] %>
#
production:
  <<: *default
  database: LuggageMGT_production
  username: root
  password: <%= ENV['DATABASE_PASSWORD'] %>
  socket: /var/lib/mysql/mysql.sock

host: dbをlocalhostにしたりしたのですが、現状何も変わっておりません。
お力を貸してください....。

Answer 1

default: &default
adapter: mysql2
encoding: utf8
pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
username: root
password: password
host: localhost
socket: /tmp/mysql.sock
のhostをdbに変えたところ解決できました！！！

Answer 2

database.yml　を載せたのは検討の方向性は正しいです。
が、Unknown MySQL server と言われているのですから、serverの情報が無いとわかりません。
default　のところに書かれているのでは？そこが合っていないのです。

Comments

[keisuke.F]

本文に追記いたしましたので、是非ご覧ください。
よろしくお願い致します。

[winterboum]

socket: /var/lib/mysql/mysql.sock があることは確認してますか

[keisuke.F]

mysql_config --socketコマンドを打ったところ、
/tmp/mysql.sock
という風に出たので、それに合わせて、
socket: /tmp/mysql.sock
という風に記述しました。本文も編集しましたのでご確認ください。

しかしながら、
Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2 "No such file or directory")
というエラーが出てしまいます。