我想删除“Mysql2 :: Error :: ConnectionError (Unknown MySQL server host 'db' (0)):”

Question

环境

- MacOS Mojave 10.14.6
- Ruby 2.6.4
- Rails 5.2.2
- mysql  Ver 8.0.17 for osx10.14 on x86_64 (Homebrew)
- Docker 2.1.0.3

我想实现什么

我想清除以下错误。

Mysql2::Error::ConnectionError (Unknown MySQL server host 'db' (0)):

终端

$ rails s
=> Booting Puma
=> Rails 5.2.2 application starting in development
=> Run `rails server -h` for more startup options
Puma starting in single mode...
* Version 3.12.1 (ruby 2.6.4-p104), codename: Llamas in Pajamas
* Min threads: 5, max threads: 5
* Environment: development
* Listening on tcp://localhost:3000
Use Ctrl-C to stop
Started GET "/" for ::1 at 2019-10-07 22:11:28 +0900

Mysql2::Error::ConnectionError (Unknown MySQL server host 'db' (0)):
...
$ docker-compose ps
      Name                    Command               State           Ports
--------------------------------------------------------------------------------
rails_test_db_1    docker-entrypoint.sh mysqld      Up       3306/tcp, 33060/tcp
rails_test_web_1   bundle exec rails s -p 300 ...   Exit 1

docker-compose.yml

version: '3'
services:
  web:
    build: .
    command: bundle exec rails s -p 3000 -b '0.0.0.0'
    volumes:
      - .:/app
    ports:
      - 3000:3000
    depends_on:
      - db
    tty: true
    stdin_open: true
  db:
    image: mysql:5.7
    volumes:
      - db-volume:/var/lib/mysql
    environment:
      MYSQL_ROOT_PASSWORD: password
volumes:
  db-volume:

数据库.yml

# MySQL. Versions 5.0 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:
#   http://dev.mysql.com/doc/refman/5.7/en/old-client.html
#
default: &default
  adapter: mysql2
  encoding: utf8
  pool: 5
  username: root
  password: password
  host: db

development:
  <<: *default
  database: app_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: app_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: app_production
  username: app
  password: <%= ENV['APP_DATABASE_PASSWORD'] %>

Answer 1

该错误告诉您主机 db 未知。

您正在终端上运行rails s。那是在 docker outside 启动您的 Rails 服务器，因此无法解析主机 db。 （对于在同一个 docker 网络中运行的容器，您只有这种 DNS 解析）

您应该只运行 docker-compose up 以便在您的 docker-compose.yml 中定义的 两个 服务（web 和 db）在同一个网络中启动（docker-compose 负责那个，你不需要为它做任何额外的设置）

Answer 2

您可以创建一个网络，该网络将在您的 docker 内的图像之间共享

networks:
  my_network:
    driver: bridge
    ipam:
      driver: default
      config:
        - subnet: 172.25.0.1/16
          gateway: 172.25.0.1

然后为您的数据库容器分配特定的 IP：

networks:
  my_network:
    ipv4_address: 172.25.0.3

之后，您需要确保 db 主机名与数据库容器 IP 链接。 下面的代码会将新行 172.25.0.3 db 添加到您的 /etc/hosts 文件中。

extra_hosts:
  - 'db:172.25.0.3'

docker-compose 的最终版本如下所示：

version: '3'
services:
  web:
    build: .
    command: bundle exec rails s -p 3000 -b '0.0.0.0'
    volumes:
      - .:/app
    ports:
      - 3000:3000
    depends_on:
      - db
    tty: true
    stdin_open: true
  extra_hosts:
    - 'db:172.25.0.3'

  db:
    image: mysql:5.7
    volumes:
      - db-volume:/var/lib/mysql
    environment:
      MYSQL_ROOT_PASSWORD: password
    networks:
      my_network:
        ipv4_address: 172.25.0.3

volumes:
  db-volume:

networks:
  my_network:
    driver: bridge
    ipam:
      driver: default
      config:
        - subnet: 172.25.0.1/16
          gateway: 172.25.0.1

如果您这样做，您可以确定db 主机将始终可用。希望对你有帮助。