Introduction

A website’s performance depends partially on the size of all the files that a user’s browser must download. Reducing the size of those transmitted files can make your website faster. It can also make your website cheaper for those who pay for their bandwidth usage on metered connections.

gzip is a popular data compression program. You can configure Nginx to use gzip to compress the files it serves on the fly. Those files are then decompressed by the browsers that support it upon retrieval with no loss whatsoever, but with the benefit of a smaller amount of data to transfer between the web server and browser. The good news is that compression support is ubiquitous among all major browsers, and there is no reason not to use it.

Because of the way compression works in general and how gzip works, certain files compress better than others. For example, text files compress very well, often ending up over two times smaller. On the other hand, images such as JPEG or PNG files are already compressed by their nature, and second compression using gzip yields little or no results. Compressing files use up server resources, so it is best to compress only files that will benefit from the size reduction.

In this tutorial, you will configure Nginx to use gzip compression. This will reduce the size of content sent to your website’s visitors and improve performance.

Checking the Default Behavior

Let’s check if the HTML file named test.html is served with compression. The command requests a file from our Nginx server and specifies that it is fine to serve gzip compressed content by using an HTTP header (Accept-Encoding: gzip):

curl -H "Accept-Encoding: gzip" -I http://localhost/test.html

In response, you should see several HTTP response headers:

Output
HTTP/1.1 200 OK
Server: nginx/1.18.0 (Ubuntu)
Date: Tue, 09 Feb 2021 19:04:25 GMT
Content-Type: text/html
Last-Modified: Tue, 09 Feb 2021 19:03:41 GMT
Connection: keep-alive
ETag: W/"6022dc8d-400"
Content-Encoding: gzip

In the last line, you can see the Content-Encoding: gzip header. This tells us that gzip compression was used to send this file. That’s because Nginx has gzip compression enabled automatically even on the fresh Ubuntu 20.04 installation.

However, by default, Nginx compresses only HTML files. Every other file will be served uncompressed, which is less than optimal. To verify that, you can request our test image named test.jpg in the same way:

curl -H "Accept-Encoding: gzip" -I http://localhost/test.jpg

Output
HTTP/1.1 200 OK
Server: nginx/1.18.0 (Ubuntu)
Date: Tue, 09 Feb 2021 19:05:49 GMT
Content-Type: image/jpeg
Content-Length: 1024
Last-Modified: Tue, 09 Feb 2021 19:03:45 GMT
Connection: keep-alive
ETag: "6022dc91-400"
Accept-Ranges: bytes

There is no Content-Encoding: gzip header in the output, which means the file was served without any compression.

You can repeat the test with the test CSS stylesheet:

curl -H "Accept-Encoding: gzip" -I http://localhost/test.css

Once again, there is no mention of compression in the output:

Output
HTTP/1.1 200 OK
Server: nginx/1.18.0 (Ubuntu)
Date: Tue, 09 Feb 2021 19:06:04 GMT
Content-Type: text/css
Content-Length: 1024
Last-Modified: Tue, 09 Feb 2021 19:03:45 GMT
Connection: keep-alive
ETag: "6022dc91-400"
Accept-Ranges: bytes

Configuring Nginx’s gzip Settings

sudo nano /etc/nginx/nginx.conf

##
# `gzip` Settings
#
#
gzip on;
gzip_disable "msie6";

gzip_vary on;
gzip_proxied any;
gzip_comp_level 6;
gzip_buffers 16 8k;
gzip_http_version 1.1;
gzip_min_length 256;
gzip_types
  application/atom+xml
  application/geo+json
  application/javascript
  application/x-javascript
  application/json
  application/ld+json
  application/manifest+json
  application/rdf+xml
  application/rss+xml
  application/xhtml+xml
  application/xml
  font/eot
  font/otf
  font/ttf
  image/svg+xml
  text/css
  text/javascript
  text/plain
  text/xml;

sudo systemctl restart nginx

Verifying the New Configuration

curl -H "Accept-Encoding: gzip" -I http://localhost/test.html

Output
HTTP/1.1 200 OK
Server: nginx/1.18.0 (Ubuntu)
Date: Tue, 09 Feb 2021 19:04:25 GMT
Content-Type: text/html
Last-Modified: Tue, 09 Feb 2021 19:03:41 GMT
Connection: keep-alive
ETag: W/"6022dc8d-400"
Content-Encoding: gzip

curl -H "Accept-Encoding: gzip" -I http://localhost/test.css

Output
HTTP/1.1 200 OK
Server: nginx/1.18.0 (Ubuntu)
Date: Tue, 09 Feb 2021 19:21:54 GMT
Content-Type: text/css
Last-Modified: Tue, 09 Feb 2021 19:03:45 GMT
Connection: keep-alive
Vary: Accept-Encoding
ETag: W/"6022dc91-400"
Content-Encoding: gzip

curl -H "Accept-Encoding: gzip" -I http://localhost/test.jpg

Output
HTTP/1.1 200 OK
Server: nginx/1.18.0 (Ubuntu)
Date: Tue, 09 Feb 2021 19:25:40 GMT
Content-Type: image/jpeg
Content-Length: 1024
Last-Modified: Tue, 09 Feb 2021 19:03:45 GMT
Connection: keep-alive
ETag: "6022dc91-400"
Accept-Ranges: bytes