PM2 nodeJS cluster mode testing with apache benchmark

Question

I've set up one nodeJS application which only has one route '/' and I'm using Nginx as a reverse proxy. So app flow is like below:

• The user sends the request to the Nginx server.
• And as per the location '/' Nginx server passes the request to the node server.

From the nodeJS, '/' route sends one HTML file as a response to the client. For load testing, I've used the apache benchmark.

Apache benchmark command used for testing:

ab -k -c 250 -n 10000 http://localhost/

Please check the apache benchmark response in the following two cases:

Case 1: When clustering mode is not on. (Without pm2, simple nodeJS server without clustering ex: node index.js)

rails@rails-laptop:~$ ab -k -c 250 -n 10000 http://localhost/
This is ApacheBench, Version 2.3 <$Revision: 1706008 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking localhost (be patient)
Completed 1000 requests
Completed 2000 requests
Completed 3000 requests
Completed 4000 requests
Completed 5000 requests
Completed 6000 requests
Completed 7000 requests
Completed 8000 requests
Completed 9000 requests
Completed 10000 requests
Finished 10000 requests


Server Software:        nginx/1.10.3
Server Hostname:        localhost
Server Port:            80

Document Path:          /
Document Length:        134707 bytes

Concurrency Level:      250
Time taken for tests:   9.531 seconds
Complete requests:      10000
Failed requests:        0
Keep-Alive requests:    10000
Total transferred:      1350590000 bytes
HTML transferred:       1347070000 bytes
Requests per second:    1049.26 [#/sec] (mean)
Time per request:       238.264 [ms] (mean)
Time per request:       0.953 [ms] (mean, across all concurrent requests)
Transfer rate:          138390.37 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.8      0       6
Processing:    38  237  77.6    213     626
Waiting:       31  230  73.8    209     569
Total:         44  237  77.5    213     626

Percentage of the requests served within a certain time (ms)
  50%    213
  66%    229
  75%    247
  80%    280
  90%    373
  95%    395
  98%    438
  99%    538
 100%    626 (longest request)

Case 2: When PM2 clustering mode in ON.(pm2 start index.js -i 4 (4 cluster))

rails@rails-laptop:~$ ab -k -c 250 -n 10000 http://localhost/
This is ApacheBench, Version 2.3 <$Revision: 1706008 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking localhost (be patient)
Completed 1000 requests
Completed 2000 requests
Completed 3000 requests
Completed 4000 requests
Completed 5000 requests
Completed 6000 requests
Completed 7000 requests
Completed 8000 requests
Completed 9000 requests
Completed 10000 requests
Finished 10000 requests


Server Software:        nginx/1.10.3
Server Hostname:        localhost
Server Port:            80

Document Path:          /
Document Length:        134707 bytes

Concurrency Level:      1
Time taken for tests:   14.109 seconds
Complete requests:      10000
Failed requests:        0
Total transferred:      1350540000 bytes
HTML transferred:       1347070000 bytes
Requests per second:    708.79 [#/sec] (mean)
Time per request:       1.411 [ms] (mean)
Time per request:       1.411 [ms] (mean, across all concurrent requests)
Transfer rate:          93481.05 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.1      0       9
Processing:     1    1   1.2      1      35
Waiting:        0    1   0.9      1      21
Total:          1    1   1.2      1      35

Percentage of the requests served within a certain time (ms)
  50%      1
  66%      1
  75%      1
  80%      1
  90%      2
  95%      3
  98%      5
  99%      6
 100%     35 (longest request)

Now, if you compare the request per second time in both the scenarios, you will see that Requests per second (1049.26 [#/sec] (mean)) when no cluster mode is used higher than the pm2 cluster mode (708.79 [#/sec] (mean)) . I don't understand why it so? As far as I know, clustering mode is used to achieve a higher level of concurrency but why there is conflict in the result?

Answer 1

I tried clustering with different parameters:

• no process

• calculation

  for(let i = 1; i <= 50000000; i++){ r += i; }

• sending file

• concurrent request count

Here is the git repo

Here is my conclusion:

• for serving files, it does not make sense to cluster. I think the network is the bottle neck here, and clustering does not help.
• for calculation it does make sense to cluster, cause it keeps the event loop busy, and if you cluster, you have multiple event loops to be kept busy. While testing with calculation, I checked the server cores processes by htop and I considered that the same amount of the clusters I had CPU's 100 percent busy. The performance multiplied by the cluster count, for example if I made 6 node cluster, the performance became 6 times more.
• it does not make sense to cluster more than CPU cores you have on the machine. I recommend to reserve one core for the OS.

I made a repository and in the readme file I wrote the detailed results.