Golang连接被拒绝问题排查与解决

连接被拒绝通常是由于网络配置或连接字符串错误导致的。从你的配置来看，主要问题在于Go应用程序连接MySQL时使用了错误的连接地址。

在你的main.go文件中，连接字符串构建有问题：

// 当前错误的连接字符串
connStr:=config.mysqlUser+":"+config.mysqlPassword+"@tcp(db:"+config.mysqlPort+")/"+config.mysqlDB

应该使用在docker-compose中定义的MySQL服务名称fullstack-mysql，而不是db：

// 正确的连接字符串
connStr := config.mysqlUser + ":" + config.mysqlPassword + "@tcp(fullstack-mysql:" + config.mysqlPort + ")/" + config.mysqlDB

另外，你的Go Dockerfile中环境变量设置有问题，应该从.env文件读取配置。修改./Go/Dockerfile：

FROM golang:alpine AS builder
ENV GO111MODULE=on
RUN mkdir /app
ADD . /app/
WORKDIR /app
COPY . .
RUN go mod init stuff.com
RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -o main .
EXPOSE 9000
CMD ["./main"]

在Go代码中，确保正确读取环境变量：

package main

import (
    "database/sql"
    "fmt"
    "log"
    "os"
    
    _ "github.com/go-sql-driver/mysql"
)

type Config struct {
    mysqlUser     string
    mysqlPassword string
    mysqlHost     string
    mysqlPort     string
    mysqlDB       string
    mysqlDriver   string
}

var config Config

func init() {
    config = Config{
        mysqlUser:     getEnv("MYSQL_USER", "docker"),
        mysqlPassword: getEnv("MYSQL_PASSWORD", "docker"),
        mysqlHost:     getEnv("MYSQL_HOST", "fullstack-mysql"),
        mysqlPort:     getEnv("MYSQL_PORT", "3306"),
        mysqlDB:       getEnv("MYSQL_DATABASE", "test_db"),
        mysqlDriver:   getEnv("MYSQL_DRIVER", "mysql"),
    }
}

func getEnv(key, defaultValue string) string {
    if value, exists := os.LookupEnv(key); exists {
        return value
    }
    return defaultValue
}

func db() error {
    // 正确的连接字符串
    connStr := fmt.Sprintf("%s:%s@tcp(%s:%s)/%s",
        config.mysqlUser,
        config.mysqlPassword,
        config.mysqlHost,  // 应该是 "fullstack-mysql"
        config.mysqlPort,
        config.mysqlDB)
    
    log.Println("Connection string:", connStr)
    
    db, err := sql.Open(config.mysqlDriver, connStr)
    if err != nil {
        log.Println("Open error:", err.Error())
        return err
    }
    defer db.Close()
    
    // 设置连接池参数
    db.SetMaxOpenConns(25)
    db.SetMaxIdleConns(25)
    db.SetConnMaxLifetime(5 * time.Minute)
    
    err = db.Ping()
    if err != nil {
        log.Println("Ping Error:", err.Error())
        return err
    }
    
    log.Println("Successfully connected to MySQL")
    return nil
}

func main() {
    // 等待MySQL服务启动
    time.Sleep(5 * time.Second)
    
    if err := db(); err != nil {
        log.Fatal("Database connection failed:", err)
    }
    
    // 你的应用逻辑
}

还需要在docker-compose.yml中确保网络配置正确，app服务应该等待MySQL完全启动：

version: '3'
services:
  fullstack-mysql:
    container_name: db_mysql
    build:
      context: ./MySQL
    ports:
      - "3306:3306"
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_DATABASE: test_db
      MYSQL_USER: docker
      MYSQL_PASSWORD: docker
    volumes:
      - database_mysql:/var/lib/mysql
    networks:
      - fullstack
    healthcheck:
      test: ["CMD", "mysqladmin", "ping", "-h", "localhost"]
      timeout: 20s
      retries: 10

  app:
    container_name: golang_app
    build:
      context: ./Go
    ports:
      - "9000:9000"
    restart: on-failure
    volumes:
      - api:/usr/src/app/
    depends_on:
      fullstack-mysql:
        condition: service_healthy
    networks:
      - fullstack
    environment:
      MYSQL_HOST: fullstack-mysql
      MYSQL_PORT: 3306
      MYSQL_USER: docker
      MYSQL_PASSWORD: docker
      MYSQL_DATABASE: test_db

  phpmyadmin:
    image: phpmyadmin/phpmyadmin
    container_name: phpmyadmin_container
    depends_on:
      - fullstack-mysql
    environment:
      PMA_HOST: fullstack-mysql
      PMA_USER: root
      PMA_PORT: 3306
      PMA_PASSWORD: root
    ports:
      - "9090:80"
    restart: always
    networks:
      - fullstack

volumes:
  api:
  database_mysql:

networks:
  fullstack:
    driver: bridge

关键点是：

1. 使用正确的服务名称fullstack-mysql而不是db
2. 添加健康检查确保MySQL完全启动后再连接
3. 在app服务中明确设置环境变量
4. 使用正确的连接字符串格式：user:password@tcp(host:port)/database