I was suffering from panic: dial tcp 127.0.0.1: 3306: connect: connection refused in Go (Gin) + MySQL Docker environment

Symptoms

As the title says.

solution

Here has the same symptoms. I corrected the MySQL connection information as I was told, and it was fixed. Below is Before / After.

Before

docker-compose.yml

version: "3"
services:
  app:
    build: .
    depends_on:
      - db
    volumes:
      - ./:/go/src/app
    ports:
      - 3000:3000
    environment:
      MYSQL_DATABASE: go_app_dev
      MYSQL_USER: docker
      MYSQL_PASSWORD: password

  db:
    image: mysql:5.7
    container_name: dockerMySQL
    volumes:
      - ./storage/mysql_data:/var/lib/mysql
    ports:
      - 3306:3306
    environment:
      MYSQL_DATABASE: go_app_dev
      MYSQL_USER: docker
      MYSQL_PASSWORD: password
      MYSQL_ROOT_PASSWORD: password

db/db.go

package db

import (
    "fmt"
    "os"
    "github.com/jinzhu/gorm"
    _ "github.com/jinzhu/gorm/dialects/mysql"
)

var (
    db  *gorm.DB
    err error
)

func Init() {
    user = os.Getenv("MySQL_USER")
    pass = os.Getenv("MYSQL_PASSWORD")
    dbname := os.Getenv("MYSQL_DATABASE")
    connection := fmt.Sprintf("%s:%s@/%s?charset=utf8&parseTime=True&loc=Local", user, pass, dbname)

    db, err := gorm.Open("mysql", connection)

    if err != nil {
        panic(err)
    }
}

After

docker-compose.yml

version: "3"
services:
  app:
    build: .
    depends_on:
      - db
    volumes:
      - ./:/go/src/app
    ports:
      - 3000:3000
    environment:
      MYSQL_DATABASE: go_app_dev
      MYSQL_HOST: dockerMySQL  #add to!!
      MYSQL_USER: docker
      MYSQL_PASSWORD: password

  db:
    image: mysql:5.7
    container_name: dockerMySQL  #add to!!
    volumes:
      - ./storage/mysql_data:/var/lib/mysql
    ports:
      - 3306:3306
    environment:
      MYSQL_DATABASE: go_app_dev
      MYSQL_USER: docker
      MYSQL_PASSWORD: password
      MYSQL_ROOT_PASSWORD: password

db/db.go

// ...Abbreviation

func Init() {
    user = os.Getenv("MySQL_USER")
    pass = os.Getenv("MYSQL_PASSWORD")
    host = os.Getenv("MYSQL_HOST")  //Here!!
    dbname := os.Getenv("MYSQL_DATABASE")
    connection := fmt.Sprintf("%s:%s@tcp(%s)/%s?charset=utf8&parseTime=True&loc=Local", user, pass, host, dbname)  //Fix!!

    db, err := gorm.Open("mysql", connection)

    if err != nil {
        panic(err)
    }
}

The deciding factor was that when specifying the connection information with the second argument of gorm.Open, ** connect with the container name of the Docker container running MySQL **. The reason I couldn't connect to MySQL with the Before code in the first place was because MySQL wasn't listening on localhost or TCP port 3306. And since the containers running with docker-compose communicate via the docker network, it is possible to connect with the container name instead of the network name, and the app container with the connection information as posted in After It seems that you can connect to the db container from. I'm not sure if this kind of understanding is correct, but w

reference

• https://stackoverflow.com/questions/57566060/panic-dial-tcp-127-0-0-13306-connect-connection-refused?newreg=105ca01eddd149d4b863abf5bf287c5b
• https://docs.docker.com/compose/networking/