NestJS+MQTT通过NodeJS/PM2运行时触发TypeError问题

问题详情 #

• 环境：NX monorepo + NestJS MQTT微服务
• 异常表现：
  • 开发环境执行yarn nx serve api时功能正常
  • 生产编译yarn nx run-many --t=build --configuration=production无报错
  • 直接运行编译后的文件node ./dist/apps/api/main.js时触发TypeError：

/home/user/Desktop/project/node_modules/mqtt/lib/client.js:701
  const resubscribe = obj.resubscribe
                          ^

TypeError: Cannot read properties of undefined (reading 'resubscribe')
    at MqttClient.subscribe (/home/user/Desktop/project/node_modules/mqtt/lib/client.js:701:27)
    at /home/user/Desktop/project/node_modules/@nestjs/microservices/server/server-mqtt.js:40:24
    at Array.forEach (<anonymous>)
    at ServerMqtt.bindEvents (/home/user/Desktop/project/node_modules/@nestjs/microservices/server/server-mqtt.js:38:28)
    at ServerMqtt.start (/home/user/Desktop/project/node_modules/@nestjs/microservices/server/server-mqtt.js:32:14)
    at ServerMqtt.listen (/home/user/Desktop/project/node_modules/@nestjs/microservices/server/server-mqtt.js:24:18)
    at /home/user/Desktop/project/node_modules/@nestjs/microservices/nest-microservice.js:107:25
    at new Promise (<anonymous>)
    at NestMicroservice.listen (/home/user/Desktop/project/node_modules/@nestjs/microservices/nest-microservice.js:106:16)

• 核心代码片段（main.ts）：

const mqtt_app = await NestFactory.createMicroservice(AppModule, {
    transport: Transport.MQTT,
    options: {
        url: process.env.MQTT_URL,
        username: process.env.MQTT_USERNAME,
        password: process.env.MQTT_PASSWORD,
    },
});
mqtt_app.listen();

• 验证点：不调用mqtt_app.listen()则无报错；注释@MessagePattern装饰器及对应处理函数后运行正常。

解决方案 #

1. 确保生产环境变量加载 #

NX开发环境会自动加载.env文件，但直接运行编译后的Node文件时不会，需手动处理：

• 安装dotenv依赖：yarn add dotenv
• 在main.ts顶部添加环境变量加载逻辑：

import * as dotenv from 'dotenv';
// 根据实际文件路径调整，例如生产环境用.env.production
dotenv.config({ path: './apps/api/.env.production' });

或运行时通过命令直接传入环境变量：MQTT_URL=mqtt://your-broker node ./dist/apps/api/main.js

2. 等待微服务启动完成 #

mqtt_app.listen()返回Promise，未等待完成时可能导致MQTT客户端未就绪就执行订阅操作，修改为：

await mqtt_app.listen();
console.log('MQTT微服务已成功启动');

3. 显式配置MQTT客户端选项 #

给MQTT options添加默认值和显式的重订阅配置，避免客户端初始化参数异常：

const mqtt_app = await NestFactory.createMicroservice(AppModule, {
    transport: Transport.MQTT,
    options: {
        url: process.env.MQTT_URL || 'mqtt://localhost:1883',
        username: process.env.MQTT_USERNAME,
        password: process.env.MQTT_PASSWORD,
        resubscribe: true, // 显式设置重订阅选项
    },
});

4. 检查编译元数据配置 #

确保NX编译时保留装饰器元数据，修改apps/api/tsconfig.app.json：

{
  "compilerOptions": {
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true
  }
}

修改后重新编译生产包：yarn nx run-many --t=build --configuration=production

内容的提问来源于stack exchange，提问作者Stefan