9 Jul 2021

Accept more HTTP requests by increasing the incoming connections

Some servers limit the incoming network connections to a certain amount, such as 128.

Limiting the incoming network connections could significantly impact the performance of your server, so it doesn’t accept more than the specified number of connections even though you have a powerful server that can handle thousands of connections simultaneously.

Linux uses the somaxconn config to limit the number of incoming connections.

The value of somaxconn might vary from one distribution to another; in Ubuntu, the default value is 4096 connections.

Run the following command to know the default value of somaxconn on your server:

sysctl net.core.somaxconn

Anyway, let’s do some benchmarking.

Please install Apache Benchmarkon your machine.

First of all, let’s change the value of somaxconn to 100:

echo 100 > /proc/sys/net/core/somaxconn

# remember to reload nginx
sudo service nginx reload

Then, use Apache Benchmark to send 500 requests:

ab -n 500 -l -c 150 -k -H "Accept-Encoding: gzip, deflate" http://example.com/

Here, I’m sending 500 requests with 150 concurrent connections.

-c concurrency: Number of multiple requests to perform at a time.


Concurrency Level:      120
Time taken for tests:   5.215 seconds
Complete requests:      500
Failed requests:        0
Non-2xx responses:      373
Keep-Alive requests:    373
Total transferred:      1280928 bytes
HTML transferred:       1039564 bytes
Requests per second:    95.88 [#/sec] (mean)
Time per request:       1251.513 [ms] (mean)
Time per request:       10.429 [ms] (mean, across all concurrent requests)
Transfer rate:          239.88 [Kbytes/sec] received

As you might have noticed, I made 500 requests, but only 127 requests have been executed successfully. The rest, which is 373, failed.

The Non-2xx responses shows the total number of the requests that return less than 200 status code in their responses.

If you try to access the website through a web browser, you might encounter a 502 Bad Gateway because Nginx can’t handle more connections.

Increase the incoming connections

This time, let’s increase the incoming connections to 1000:

 echo 1000 > /proc/sys/net/core/somaxconn

And then let’s execute the same benchmarking command, but with 1000 requests instead of 500:

ab -n 1000 -l -c 200 -k -H "Accept-Encoding: gzip, deflate"


Concurrency Level:      200
Time taken for tests:   39.830 seconds
Complete requests:      1000
Failed requests:        0
Keep-Alive requests:    0
Total transferred:      9066911 bytes
HTML transferred:       7698000 bytes
Requests per second:    25.11 [#/sec] (mean)
Time per request:       7966.077 [ms] (mean)
Time per request:       39.830 [ms] (mean, across all concurrent requests)
Transfer rate:          222.30 [Kbytes/sec] received

This time all the 1000 request were succeed.

If you restart your server, then the value of the somaxconn will be lost, so to persist it, let’s create a new configuration file in /etc/sysctl.d/ folder:

echo "net.core.somaxconn=10000" > /etc/sysctl.d/network-tunning.conf

As you might have noticed, this time I increased the value of somaxconn to 10.000, which should be fine.

I hope you enjoyed reading this short post.