Docker Compose环境下Golang与PostgreSQL连接被拒绝问题求助

我正尝试通过Docker Compose实现Golang CLI应用flow与PostgreSQL的连接，该应用用于预算信息的创建、查看、调整、查询与删除。执行docker-compose up -d后，成功生成flow-budget_planner与postgres两个镜像，但仅启动了PostgresContainer一个容器。

执行以下命令时的情况：

• 运行docker exec -it <Container-ID> psql -U postgresql可正常进入PostgreSQL终端操作数据库；
• 单独运行docker run -it -e POSTGRES_PASSWORD=password postgres时，收到database system is ready to accept connections提示；
• 在Postgres镜像运行时，另开终端执行docker run -it flow-budget_planner ./flow budget create -c category -a 300，出现连接被拒绝的错误。

项目相关文件如下：

目录结构 #

├── CODE_OF_CONDUCT.md
├── CONTRIBUTING.md
├── Dockerfile
├── LICENSE
├── README.md
├── cmd
│   ├── budget
│   │   ├── budget.go
│   │   └── handler
│   │       ├── adjust.go
│   │       ├── create.go
│   │       ├── get.go
│   │       ├── remove.go
│   │       └── view.go
│   └── other services
│       └── service.go
├── db
│   └── budget_db
│       ├── connection.go
│       └── migrations
│           └── 001_create_budget_table.sql
├── docker-compose.yml
├── go.mod
├── go.sum
└── internal
    ├── app
    │   └── budget
    │       └── budget.go
    └── middleware
        └── env.go

PostgreSQL连接代码 #

type Variables struct {
    Host     string
    Port     string
    User     string
    Password string
    DBName   string
    SSLMode  string
}

func Connection() (*sql.DB, error) {
    v := Variables{
        Host:     middleware.LoadEnvVariable("host"),
        Port:     middleware.LoadEnvVariable("port"),
        User:     middleware.LoadEnvVariable("user"),
        Password: middleware.LoadEnvVariable("password"),
        DBName:   middleware.LoadEnvVariable("dbname"),
        SSLMode:  middleware.LoadEnvVariable("sslmode"),
    }

    connectionString := fmt.Sprintf("host=%s port=%s user=%s password=%s dbname=%s sslmode=%s", v.Host, v.Port, v.User, v.Password, v.DBName, v.SSLMode)
    db, err := sql.Open("postgres", connectionString)
    if err != nil {
        return nil, err
    }

    err = db.Ping()
    if err != nil {
        return nil, err
    }
    return db, nil
}

Dockerfile #

FROM golang:1.22.0-alpine3.19

RUN mkdir -p /app

WORKDIR /app

COPY go.mod /app
COPY go.sum /app

COPY . /app

RUN go mod download

RUN go build -o flow .

CMD ["./flow", "budget"]

Docker Compose文件 #

version: "3.8"
services:
  postgres:
    image: postgres:latest
    hostname: localhost
    container_name: PostgresContainer
    restart: always
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: password
      POSTGRES_DB: flow
    ports:
      - '5432:5432'
    volumes:
      - postgres_data:/var/lib/postgresql/data
    

  budget_planner:
    build:
      context: .
      dockerfile: Dockerfile
    depends_on:
      - postgres
    environment:
      DATABASE_URL: postgresql://postgres:password@localhost:5432/flow


volumes:
  postgres_data:
    driver: local

1. 修复budget_planner容器未启动的问题 #

budget_planner容器未启动的核心原因是默认CMD ["./flow", "budget"]执行后直接退出（CLI应用无持续运行逻辑）。

• 先查看容器日志确认原因：

  docker logs flow-budget_planner
  

• 修改Dockerfile的CMD为持续运行命令，让容器保持存活：

  # 替换原CMD
  CMD ["tail", "-f", "/dev/null"]
  

  之后重新构建镜像并启动：

  docker-compose up -d --build
  

2. 修复数据库连接被拒绝的问题 #

核心问题：容器间网络寻址错误 #

Docker Compose中，容器间需通过服务名而非localhost通信，你的Go代码读取的是单独的环境变量而非DATABASE_URL，需同步修正：

步骤1：修正Docker Compose环境变量

修改budget_planner的环境变量，将数据库主机改为PostgreSQL服务名postgres，同时补充Go代码所需的所有变量：

budget_planner:
  build:
    context: .
    dockerfile: Dockerfile
  depends_on:
    - postgres
  environment:
    host: postgres
    port: 5432
    user: postgres
    password: password
    dbname: flow
    sslmode: disable

步骤2：添加数据库连接重试机制

depends_on仅保证容器启动顺序，不保证PostgreSQL服务就绪，需在Go代码中添加重试逻辑：

import "time"

func Connection() (*sql.DB, error) {
    v := Variables{
        Host:     middleware.LoadEnvVariable("host"),
        Port:     middleware.LoadEnvVariable("port"),
        User:     middleware.LoadEnvVariable("user"),
        Password: middleware.LoadEnvVariable("password"),
        DBName:   middleware.LoadEnvVariable("dbname"),
        SSLMode:  middleware.LoadEnvVariable("sslmode"),
    }

    connectionString := fmt.Sprintf("host=%s port=%s user=%s password=%s dbname=%s sslmode=%s", v.Host, v.Port, v.User, v.Password, v.DBName, v.SSLMode)
    
    var db *sql.DB
    var err error
    // 重试5次，每次间隔2秒
    for i := 0; i < 5; i++ {
        db, err = sql.Open("postgres", connectionString)
        if err == nil {
            err = db.Ping()
            if err == nil {
                break
            }
        }
        time.Sleep(2 * time.Second)
    }
    if err != nil {
        return nil, err
    }
    return db, nil
}

步骤3：正确执行CLI命令

通过Docker Compose进入存活的budget_planner容器执行命令：

docker-compose exec budget_planner ./flow budget create -c category -a 300

3. 其他细节修正 #

• 修正PostgreSQL登录命令的用户名错误：psql -U posgresql改为psql -U postgres；
• 确保数据库迁移脚本执行：可在CLI命令执行前，手动进入容器运行迁移，或在Go代码中添加自动迁移逻辑。

内容的提问来源于stack exchange，提问作者Kaifah Habibi