nodejs concurrent multiple requests 502

Recently, I encountered a problem when using nodejs: when sending multiple concurrent requests, a 502 error will be returned. I spent some time researching this problem and finally found a solution. In this article, I will share my experience in the hope of helping others with the same problem.

First of all, we need to understand what a 502 error is. A 502 error means that the server cannot correctly handle a request from a client, usually because an error or timeout occurred during the request. In nodejs, this error is usually caused by the request being blocked or the request's timeout being set incorrectly.

Next, let’s take a look at how to send multiple concurrent requests in nodejs. In nodejs, we can use async.parallel to send multiple concurrent requests. The sample code is as follows:

const async = require('async');
const request = require('request');

const urls = [
  'https://www.example.com/page1',
  'https://www.example.com/page2',
  'https://www.example.com/page3',
  // Add more URLs here.
];

async.parallel(
  urls.map(url => callback => request(url, (err, res, body) => callback(err, body))),
  (err, results) => {
    if (err) {
      console.error(err);
      return;
    }

    console.log(results);
  },
);

In the above code, we use async.parallel to send multiple requests in parallel. We put the URLs we want to request in an array and then use the map function to convert them into a set of requests. We then use async.parallel to send these requests in parallel and collect the results when the request completes.

Now let’s take a look at how to solve the 502 error. In my research, I found that 502 errors are usually caused by a blocked request or an incorrectly set timeout for the request. If a request is blocked, it may be because we don't have a callback function that handles the request correctly, or because we don't release the resource during the request.

One way is to use the keep-alive option provided by the requests library. The keep-alive option allows requests to be kept in the connection pool and reuse existing TCP connections, thereby reducing the load on the server and improving performance. We can add this to the request options:

const request = require('request').defaults({ forever: true });

Another way is to avoid the request being blocked by adding a timeout option to the request. We can add the timeout option to the request option:

const request = require('request').defaults({ timeout: 5000 });

The above code sets the timeout to 5000 milliseconds, which means that if the request exceeds 5 seconds, a timeout error will be thrown.

Finally, if you are also encountering 502 errors, you can try sending the requests in batches instead of all at once. Doing so can reduce the load on the server and reduce the probability of 502 errors. The sample code is as follows:

const async = require('async');
const request = require('request').defaults({ timeout: 5000 });

const urls = [
  'https://www.example.com/page1',
  'https://www.example.com/page2',
  'https://www.example.com/page3',
  // Add more URLs here.
];

const chunkSize = 2; // Set the maximum number of requests to send at once.

async.eachLimit(
  urls,
  chunkSize,
  (url, callback) => request(url, (err, res, body) => callback(err, body)),
  (err) => {
    if (err) {
      console.error(err);
      return;
    }

    console.log('All requests completed successfully.');
  },
);

In the above code, we divide the requests into groups of two and use async.eachLimit to limit the maximum number of requests sent at one time. Doing so can reduce the load on the server and reduce the probability of 502 errors.

In short, if you encounter the problem of nodejs concurrent request 502 error, you can try to use the above method to solve it. By paying attention to request callback functions and timeout settings, you can reduce the possibility of request blocking. In addition, sending requests in batches can avoid overload situations and reduce the probability of 502 errors.

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