node.js - 如何在 AWS Lambda 中等待异步操作？

Question

我正在尝试在 S3 中处理上传的文件。由于 getObject 是异步主函数在处理完成之前结束，AWS 在 3-4 秒内杀死 lambda。

更糟糕的是，处理方法中还有异步操作——它会进行 http 调用。

在高层次上，我的代码如下所示:

exports.handler = function(event, context) {
    // Get the object from the event and show its content type
    var bucket = event.Records[0].s3.bucket.name;
    var key = event.Records[0].s3.object.key;
    var params = {
        Bucket: bucket,
        Key: key
    };
    s3.getObject(params, function(err, data) {
        if (err) {
             ...
        } else {
            processFile(data.Body.toString(), 0);
            console.log("ok");
        }
    });
    //need to wait here till processFile is done
};

processFile = function(content, start) {
  ... build url to call
  http.get(url, function(res) {  
    console.log("Got response: " + res.statusCode + ");
    processFile(content, start + 1);
  });
}

我发现nodejs中有异步但亚马逊不包含它； require('async') 或 require('sleep) 都会导致错误。

Lambda 超时配置为 60 秒，但在 3-4 秒后退出。

Answer 1

开发人员的生活在不断变化，现在我们在 lambda 上使用了 NodeJS 8。对于正在查看此内容的任何人，请查看:

Lambda Node 8.10 与 Node 6.10 比较: https://aws.amazon.com/blogs/compute/node-js-8-10-runtime-now-available-in-aws-lambda/

JS 异步的基础知识: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function

更多 aws sdk 示例:https://docs.aws.amazon.com/sdk-for-javascript/v2/developer-guide/using-promises.html

.promise() 方法的详细信息在第一个链接中:https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/Request.html#promise-property

这是我对一个基本示例的看法(尝试粘贴到您自己的 lambda 中):

exports.handler = async (event) => {    
    function wait(){
        return new Promise((resolve, reject) => {
            setTimeout(() => resolve("hello"), 2000)
        });
    }
    
    console.log(await wait());
    console.log(await wait());
    console.log(await wait());
    console.log(await wait());
    console.log(await wait());
    console.log(await wait());
    
    return 'exiting'
};

以上产出:

如您所见，它等待了 12 秒而没有杀死我的功能 :)

每次等待要多做一件事，使用 Promise.all([]) 语法如下:

exports.handler = async (event) => {
    var uploadPromises = [];
    folder.files.forEach(file => {
        uploadPromises.push( s3.putObject({
            Bucket: "mybucket",
            Key: file.name,
            Body: file.data
        }).promise());
    });

    await Promise.all(uploadPromises);
    return 'exiting'
}; 

下面是原始答案

我手上也有同样的问题。

问题是 javascript 事件循环是空的，所以 Lambda 认为它已经完成了。

这就是我解决这个问题的方法。我意识到这并不理想，我希望有更好的方法，但我不想 a) 添加库，b) 协调 lambda 调用，或 c) 切换到另一种语言。

最终它会起作用。

    exports.handler = (event, context, callback) => {
        var response;
        var callBackCount;

        /*
        Ensures the javascript event loop is never empty.
        This is the key to keeping lambda from exiting early
        */
        setInterval(function(){}, 1000);

        /*
        Tell lambda to stop when I issue the callback.
        This is super important or the lambda funciton will always go until it hits the timeout limit you set.
        */
        context.callbackWaitsForEmptyEventLoop = false;
        
        //My way of determining when I'm done with all calls
        callBackCount = 0;
      
        //My info to return
        response = "";
        
        //Various functions that make rest calls and wait for a response
        asyncFunction1();
        asyncFunction2();
        asyncFunction3();

        //Same for asyncFunction 2 and 3
        function asyncFunction1(){
          response += callBackResponseForThisMethod;
      
          returnResponse();
        }

        function returnReponse(){
            callBackCount++;

            if(callBackCount == 3){
              //Lambda will stop after this as long as    context.callbackWaitsForEmptyEventLoop was set to false 
              callback(null, JSON.stringify(response));
            }
        }

    };

http://docs.aws.amazon.com/lambda/latest/dg/nodejs-prog-model-context.html