返回承诺不适用于 AWS 开发工具包

Question

我创建了一个 API，它调用 get cloudWatch AWS API 并返回可以在我的应用程序上绘制的数据点。我对每个包都有单独的路由（如下面的路由代码所示）。此 API 使用 REST MVC 方法。

所以我正在用我的函数做几件事。

1. 从 SQLite3 数据库中读取 EC2 实例数据以获取 有关正在运行的实例的信息（IP、instance_id、 instance_launchtime) 以便我可以将其放入所需的参数中 用于 AWS 开发工具包中的 getMetricStatistics API。

2. 然后将来自第 1 步的数据放入一个参数数组（3 个参数以 3 个不同的度量数据点响应）。这会循环遍历每个参数，将其插入到 getMetricStatistics API（一个接一个，因为 getMetricStatistics 不会一次接受多个指标）以获取该实例的数据点并将它们推送到一个数组中。

我相信数据库是异步的，这就是我对它附加承诺的原因。 当我将端点加载到浏览器中时，它只会继续加载并且不会显示任何数据。但是，当我刷新页面时，它会正确显示所有结果...

这是我的 API 控制器：

// Return results sent from Cloud Watch API
const InsightModel = require('../models/insight.model.js');
const cloudWatch = InsightModel.cloudWatch;
const CWParams = InsightModel.CWParams;
const packageById = InsightModel.packageById;

let cpuUtilParam;
let cpuCBParam;
let cpuCUParam;
let insightParams = [];
let metricResults = [];
exports.getAnalytics = (req, res) => {
  const currentDate = new Date().toISOString();
  let promise1 = new Promise((resolve, reject) => {
    packageById(req.params.packageKey, (err, data) => {
      if (err) {
        reject(
          res.status(500).send({
            message:
              err.message ||
              'Error while getting the insight configuration data.',
          })
        );
      } else {
        cpuUtilParam = new CWParams(
          currentDate,
          'CPUUtilization',
          'AWS/EC2',
          data[0].launch_time,
          data[0].instance_id
        );
        cpuCBParam = new CWParams(
          currentDate,
          'CPUCreditBalance',
          'AWS/EC2',
          data[0].launch_time,
          data[0].instance_id
        );
        cpuCUParam = new CWParams(
          currentDate,
          'CPUCreditUsage',
          'AWS/EC2',
          data[0].launch_time,
          data[0].instance_id
        );
        insightParams = [cpuUtilParam, cpuCBParam, cpuCUParam];
          resolve(insightParams);
      }
    });
  })
  let promise2 = new Promise((resolve, reject) => {
    insightParams.forEach(metric => {
      cloudWatch.getMetricStatistics(metric, function(err, data) {
        if (err) {
          reject(
            res.status(500).send({
              messaage:
                err.message ||
                'Error occured while running cloudWatch getMetricStatistcs API: ',
            })
          );
        } else {
          metricResults.push(data);
          if (metricResults.length === insightParams.length)
            resolve(metricResults);
        }
      });
    });
  });

  Promise.all([promise1, promise2])
    .then(metricResults => {
      res.send(metricResults);
      console.log('AWS CW API successful');
    })
    .catch(err => {
      res.status(500).send({
        messaage:
          err.message ||
          'Error occured while reading in a promise from cloudWatch getMetricStatistcs API: ',
      })
    });
  metricResults = [];
};

API 的模型：

// Call AWS Cost Explorer API
const AWS = require('aws-sdk');
const config = require('./AWSconfig');
const database = require('./db');

const insightdb = database.insightdb;

AWS.config.update({
  accessKeyId: config.accessKeyId,
  secretAccessKey: config.secretAccessKey,
  region: config.region,
});

//Linking AWS CloudWatch Service
var cloudWatch = new AWS.CloudWatch();

const packageById = (packageId, callback) => {
  insightdb.all(
    'SELECT * FROM ec2Instance WHERE package_id == ?',
    packageId,
    (err, rows) => {
      if (err) {
        callback(err, null);
      } else {
        callback(null, rows);
      }
    }
  );
};

// Parameter class to feed into the CloudWatch getMetricStatistics function
const CWParams = function(reqDate, metricName,service,launchTime,instanceId) {
  (this.EndTime = reqDate) /* required */,
    (this.MetricName = metricName) /* required */,
    (this.Namespace = service) /* required */,
    (this.Period = 3600) /* required */,
    (this.StartTime = launchTime) /* ${createDate}`, required */,
    (this.Dimensions = [
      {
        Name: 'InstanceId' /* required */,
        Value: instanceId /* required */,
      },
    ]),
    (this.Statistics = ['Maximum']);
};

//Exports variables to the controller (so they can be re-used)
module.exports = { cloudWatch, CWParams, packageById };

API 的路由：

module.exports = app => {
  const insight = require('../controllers/insight.controller.js');
  app.get('/insights/aws/:packageKey', insight.getAnalytics);
};

Answer 1

就目前而言，在第二个 Promise 构造函数中，insightParams 保证尚未组合，因为 insightParams = [.....] 位于异步调用的回调中。因此，程序流程需要确保所有“promise2”的东西只有在“promise1”完成后才会发生。

如果异步函数在尽可能低的级别被“承诺”，那么在更高级别的代码中事情会变得简单得多。所以在模型中做两件事：

• 承诺cloudWatch.getMetricStatistics()
• 编写 packageById() 以返回 Promise 而不是接受回调。

模型因此变为：

const AWS = require('aws-sdk'); // no change
const config = require('./AWSconfig'); // no change
const database = require('./db'); // no change

const insightdb = database.insightdb; // no change

AWS.config.update({
    accessKeyId: config.accessKeyId,
    secretAccessKey: config.secretAccessKey,
    region: config.region
}); // no change

var cloudWatch = new AWS.CloudWatch(); // no change

// Promisify cloudWatch.getMetricStatistics() as  cloudWatch.getMetricStatisticsAsync().
cloudWatch.getMetricStatisticsAsync = (metric) => {
    return new Promise((resolve, reject) => {
        cloudWatch.getMetricStatistics(metric, function(err, data) {
            if (err) {
                if(!err.message) { // Probably not necessary but here goes ...
                    err.message = 'Error occured while running cloudWatch getMetricStatistcs API: ';
                }
                reject(err); // (very necessary)
            } else {
                resolve(data);
            }
        });
    });
};

// Ensure that packageById() returns Promise rather than accepting a callback.
const packageById = (packageId) => {
    return new Promise((resolve, reject) => {
        insightdb.all('SELECT * FROM ec2Instance WHERE package_id == ?', packageId, (err, rows) => {
            if (err) {
                reject(err);
            } else {
                resolve(rows);
            }
        });
    });
};

现在getAnalytics()可以这样写：

exports.getAnalytics = (req, res) => {
    packageById(req.params.packageKey)
    .then(data => {
        const currentDate = new Date().toISOString();
        let insightParams = [
            new CWParams(currentDate, 'CPUUtilization', 'AWS/EC2', data[0].launch_time, data[0].instance_id),
            new CWParams(currentDate, 'CPUCreditBalance', 'AWS/EC2', data[0].launch_time, data[0].instance_id),
            new CWParams(currentDate, 'CPUCreditUsage', 'AWS/EC2', data[0].launch_time, data[0].instance_id)
        ];
        // Composition of `insightParams` is synchronous so you can continue 
        // with the `cloudWatch.getMetricStatisticsAsync()` stuff inside the same .then().
        return Promise.all(insightParams.map(metric => cloudWatch.getMetricStatisticsAsync(metric))); // Simple because of the Promisification above.
    }, err => {
        // This callback handles error from packageById() only,
        // and is probably unnecessary but here goes ...
        if(!err.message) {
            err.message = 'Error while getting the insight configuration data.';
        }
        throw err;
    })
    .then(metricResults => {
        res.send(metricResults);
        console.log('AWS CW API successful');
    })
    .catch(err => {
        // Any async error arising above will drop through to here.
        res.status(500).send({
            'message': err.message
        }));
    });
};

请注意，不需要多个带有res.status(500).send() 的捕获。沿着 Promise 链向下传播的错误允许单个终端 .catch()