dockerでのrspec実行時のエラー Unknown MySQL server host 'db' (-2)

Question

前提・実現したいこと

rspecの実行時に下記のエラーが出てしまっており、テストの実行ができません。
開発環境、本番環境ともに新規投稿やユーザー作成は行えており、テストの実行のみ行えない状況です。

発生している問題・エラーメッセージ

Failure/Error: ActiveRecord::Migration.maintain_test_schema!

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

該当のソースコード

rails_helper.rb
# This file is copied to spec/ when you run 'rails generate rspec:install'
require 'spec_helper'
ENV['RAILS_ENV'] ||= 'test'

require File.expand_path('../config/environment', __dir__)

# Prevent database truncation if the environment is production
abort("The Rails environment is running in production mode!") if Rails.env.production?
require 'rspec/rails'
# Add additional requires below this line. Rails is not loaded until this point!

# Requires supporting ruby files with custom matchers and macros, etc, in
# spec/support/ and its subdirectories. Files matching `spec/**/*_spec.rb` are
# run as spec files by default. This means that files in spec/support that end
# in _spec.rb will both be required and run as specs, causing the specs to be
# run twice. It is recommended that you do not name files matching this glob to
# end with _spec.rb. You can configure this pattern with the --pattern
# option on the command line or in ~/.rspec, .rspec or `.rspec-local`.
#
# The following line is provided for convenience purposes. It has the downside
# of increasing the boot-up time by auto-requiring all files in the support
# directory. Alternatively, in the individual `*_spec.rb` files, manually
# require only the support files necessary.
#
# Dir[Rails.root.join('spec', 'support', '**', '*.rb')].each { |f| require f }

# Checks for pending migrations and applies them before tests are run.
# If you are not using ActiveRecord, you can remove these lines.
begin
  # ActiveRecord::Migration.maintain_test_schema!
rescue ActiveRecord::PendingMigrationError => e
  puts e.to_s.strip
  exit 1
end
RSpec.configure do |config|
  # Remove this line if you're not using ActiveRecord or ActiveRecord fixtures
  config.fixture_path = "#{::Rails.root}/spec/fixtures"

  # If you're not using ActiveRecord, or you'd prefer not to run each of your
  # examples within a transaction, remove the following line or assign false
  # instead of true.
  config.use_transactional_fixtures = true

  # RSpec Rails can automatically mix in different behaviours to your tests
  # based on their file location, for example enabling you to call `get` and
  # `post` in specs under `spec/controllers`.
  #
  # You can disable this behaviour by removing the line below, and instead
  # explicitly tag your specs with their type, e.g.:
  #
  #     RSpec.describe UsersController, :type => :controller do
  #       # ...
  #     end
  #
  # The different available types are documented in the features, such as in
  # https://relishapp.com/rspec/rspec-rails/docs
  config.infer_spec_type_from_file_location!

  # Filter lines from Rails gems in backtraces.
  config.filter_rails_from_backtrace!
  # arbitrary gems may also be filtered via:
  # config.filter_gems_from_backtrace("gem name")
end

docker-compose.yml
version: '3'
services:
  db:
    image: mysql:5.7
    ports:
      - "4306:3306"
    env_file: db.env

  web:
    build: .
    command: bash -c "rm -f tmp/pids/server.pid && bundle exec rails s -p 3000 -b '0.0.0.0'"
    volumes:
      - .:/app_name
    ports:
      - "3000:3000"
    depends_on:
      - db
    image: mysql:5.7
    env_file: db.env
    tty: true
    stdin_open: true

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: <%= ENV.fetch('DB_USERNAME', 'root') %>
  password: <%= ENV.fetch('DB_PASSWORD', 'password') %>
  socket: /tmp/mysql.sock
  host: <%= ENV.fetch('DB_HOST', 'db') %>

development:
  <<: *default
  database: study-log_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: study-log_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
  adapter: postgresql
  encoding: unicode
  pool: 5

試したこと

docker-composeに下記追加
web: image: mysql:5.7

database.ymlのhost部分を下記のように修正したがうまくいかず
host: db

rails_helper.rbの下記部分の記述コメントアウト
ActiveRecord::Migration.maintain_test_schema!

補足情報（FW/ツールのバージョンなど）

ruby '2.6.3'
rails '5.2.3'

Answer 1

MySQLにsocketで接続するような設定になっていますが、webコンテナの方にはsocketが存在しないので繋がらないと思います

以下のようにnamed volumeを使うと良いかと思います

services:
  db:
    volumes:
    - "socket-data:/tmp/mysql.sock"
  web:
    volumes:
    - "socket-data:/tmp/mysql.sock"
volumes:
  socket-data

Comments

[yoohe0722]

回答ありがとうございます！
docker-compose.ymlを下記のように編集したところ、

``` docker-compose.yml
version: '3'
services:
db:
image: mysql:5.7
ports:
- "4306:3306"
env_file: db.env
volumes:
- "socket-data:/tmp/mysql.sock"

web:
build: .
command: bash -c "rm -f tmp/pids/server.pid && bundle exec rails s -p 3000 -b '0.0.0.0'"
volumes:
- "socket-data:/tmp/mysql.sock"
ports:
- "3000:3000"
depends_on:
- db
env_file: db.env
tty: true
stdin_open: true
volumes:
socket-data
```

docker-compose build を実行すると下記のエラーが出ました。
`ERROR: In file './docker-compose.yml', volume must be a mapping, not a string.`

調べたところ、文末に：が必要なようだったので、
`socket-data:`
とすると無事build自体はできました。

しかし、rspecを実行すると下記のエラーが出て実行できませんでした。
`Unknown MySQL server host 'db' (0)`

他になにか考えられる原因はありますでしょうか？

[退会済みユーザー]

MySQLのsocketの場所が違うとかでしょうか