How to manage a queue in nodejs?

Question

I have written a script in Nodejs that takes a screenshot of websites(using slimerJs), this script takes around 10-20 seconds to complete, the problem here is the server is stalled until this script has is finished.

app.get('/screenshot', function (req, res, next) {
  var url = req.query.url;
  assert(url, "query param 'url' needed");
  // actual saving happens here
  var fileName = URL.parse(url).hostname + '_' + Date.now() + '.png';
  var command = 'xvfb-run -a -n 5 node slimerScript.js '+ url + ' '+ fileName;
  exec(command, function (err, stdout, stderror) {
    if(err){ return next(err); }
    if(stderror && (stderror.indexOf('error')!= -1) ){ return next(new Error('Error occurred!')); }
    return res.send({
      status: true,
      data: {
        fileName: fileName,
        url: "http://"+path.join(req.headers.host,'screenshots', fileName)
      }
    });
  })
});

Since the script spawns a firefox browser in memory and loads the website, the ram usage can spike upto 600-700mb, and thus i cannot execute this command asynchronously as ram is expensive on servers.

may i know if its possible to queue the incoming requests and executing them in FIFO fashion?

i tried checking packages like kue, bull and bee-queues, but i think these all assume the job list is already known before the queue is started, where as my job list depends on users using the site, and i wanna also tell people that they are in queue and need to wait for their turn. is this possible with the above mentioned packages?

Answer 1

If I were doing the similar thing, I would try these steps.

1.An array(a queue) to store requested info, when any request come, store those info in the array, and send back a msg to users, telling them they are in the queue, or the server is busy if there are already too many requests.

2.Doing the screen shot job, async, but not all in the same time. You could start the job if you find the queue is empty when a new request comes, and start another recursively when you finish the last one.

function doSceenShot(){
  if(a.length > 1){
    execTheJob((a[0])=>{
      //after finishing the job;
      doScreenShot()
    })
  }
}

3.Notify the user you've finished the job, via polling or other ways.