egg life cycle

As an enterprise-level node framework, egg has agreed on some rules on the basis of encapsulation and integrated it into the framework. Such as plugins, service, extend, etc. At the same time, egg implements a set of life cycle mechanisms in order to allow users to better participate in the application startup process.

The egg life cycle provides a unified entry file app.js, this file returns a boot class, and different life cycle functions are provided in the boot class.

There are 7 life cycles in total, from configuration file loading, to file loading, to plug-in startup, worker ready, application startup and shutdown. details as follows:

1. configWillLoad The configuration file is about to be loaded, and the configuration can be dynamically modified in this life cycle

2, configDidLoad configuration file loading is complete

3. didLoad file loading is complete

4. The willReady plugin is started

5. didReady worker is ready

6. serverDidReady The application is started

7, beforeClose application is about to close

Example:

// app.js
class AppBootHook {
  constructor(app) {
    this.app = app;
  }

  configWillLoad() {
    // 此时 config 文件已经被读取并合并，但是还并未生效
    // 这是应用层修改配置的最后时机
    // 注意：此函数只支持同步调用

    // 例如：参数中的密码是加密的，在此处进行解密
    this.app.config.mysql.password = decrypt(this.app.config.mysql.password);
    // 例如：插入一个中间件到框架的 coreMiddleware 之间
    const statusIdx = this.app.config.coreMiddleware.indexOf('status');
    this.app.config.coreMiddleware.splice(statusIdx + 1, 0, 'limit');
  }

  async didLoad() {
    // 所有的配置已经加载完毕
    // 可以用来加载应用自定义的文件，启动自定义的服务

    // 例如：创建自定义应用的示例
    this.app.queue = new Queue(this.app.config.queue);
    await this.app.queue.init();

    // 例如：加载自定义的目录
    this.app.loader.loadToContext(path.join(__dirname, 'app/tasks'), 'tasks', {
      fieldClass: 'tasksClasses',
    });
  }

  async willReady() {
    // 所有的插件都已启动完毕，但是应用整体还未 ready
    // 可以做一些数据初始化等操作，这些操作成功才会启动应用

    // 例如：从数据库加载数据到内存缓存
    this.app.cacheData = await this.app.model.query(QUERY_CACHE_SQL);
  }

  async didReady() {
    // 应用已经启动完毕

    const ctx = await this.app.createAnonymousContext();
    await ctx.service.Biz.request();
  }

  async serverDidReady() {
    // http / https server 已启动，开始接受外部请求
    // 此时可以从 app.server 拿到 server 的实例

    this.app.server.on('timeout', socket => {
      // handle socket timeout
    });
  }
}

module.exports = AppBootHook;