A previous version of this tutorial was written by Sergey Zhukaev.

Introduction

Nginx is a fast and reliable open-source web server. It gained its popularity due to its low memory footprint, high scalability, ease of configuration, and support for a wide variety of protocols.
HTTP/2 is a new version of the Hypertext Transport Protocol, which is used on the Web to deliver pages from server to browser. HTTP/2 is the first major update of HTTP in almost two decades: HTTP1.1 was introduced to the public back in 1999 when webpages were usually just a single HTML file with inline CSS stylesheet. The Internet has dramatically changed since then, and now we are facing the limitations of HTTP 1.1 — the protocol limits potential transfer speeds for most modern websites because it downloads parts of a page in a queue (the previous part must download completely before the download of the next part begins), and an average modern webpage requires about 100 request to be downloaded (each request is a picture, js file, css file, etc).
HTTP/2 solves this problem because it brings a few fundamental changes:

All requests are downloaded in parallel, not in a queue
HTTP headers are compressed
Pages transfer as a binary, not as a text file, which is more efficient
Servers can “push” data even without the user’s request, which improves speed for users with high latency

Even though HTTP/2 does not require encryption, developers of two most popular browsers, Google Chrome and Mozilla Firefox, stated that for the security reasons they will support HTTP/2 only for HTTPS connections. Hence, if you decide to set up servers with HTTP/2 support, you must also secure them with HTTPS.
This tutorial will help you set up a fast and secure Nginx server with HTTP/2 support.

Prerequisites

Before we get started, we will need a few things:

One Ubuntu 18.04 server set up by following the Ubuntu 18.04 initial server setup guide, including a sudo non-root user and a firewall.
Nginx installed on your server, which you can do by following How To Install Nginx on Ubuntu 18.04.
A domain name configured to point to your server. You can purchase one on Namecheap or get one for free on Freenom. You can learn how to point domains to DigitalOcean Droplets by following the documentation on How To Manage Your Domain With DigitalOcean.
A TLS/SSL certificate configured for your server. You have three options:

You can get a free certificate from Let’s Encrypt by following How to Secure Nginx with Let’s Encrypt on Ubuntu 18.04.
You can also generate and configure a self-signed certificate by following How to Create a Self-signed SSL Certificate for Nginx in Ubuntu 18.04.
You can buy one from another provider and configure Nginx to use it by following Steps 2 through 6 of  How to Create a Self-signed SSL Certificate for Nginx in Ubuntu 18.04.

Nginx configured to redirect traffic from port 80 to port 443, which should be covered by the previous prerequisites.
Nginx configured to use a 2048-bit or higher Ephemeral Diffie-Hellman (DHE) key, which should also be covered by the previous prerequisites.

Step 1 — Enabling HTTP/2 Support

If you followed the server block set up step in the Nginx installation tutorial, you should have a server block for your domain at /etc/nginx/sites-available/your_domain with the server_namedirective already set appropriately. The first change we will make will be to modify your domain’s server block to use HTTP/2.
Open the configuration file for your domain:

sudo nano /etc/nginx/sites-available/your_domain

In the file, locate the listen variables associated with port 443:
/etc/nginx/sites-available/<^>your_domain<^>

...
    listen [::]:443 ssl ipv6only=on; 
    listen 443 ssl; 
...

The first one is for IPv6 connections. The second one is for all IPv4 connections. We will enable HTTP/2 for both.
Modify each listen directive to include http2:
/etc/nginx/sites-available/<^>your_domain<^>

...
    listen [::]:443 ssl http2 ipv6only=on; 
    listen 443 ssl http2; 
...

This tells Nginx to use HTTP/2 with supported browsers.
Save the configuration file and exit the text editor.
Whenever you make changes to Nginx configuration files, you should check the configuration for syntax errors, like this:

sudo nginx -t

If the syntax is error-free, you will see the following output:
of sudo nginx -t

nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful

Next, we’ll configure our server to use a more restrictive list of ciphers.

Step 2 — Removing Old and Insecure Cipher Suites

HTTP/2 has a blacklist of old and insecure ciphers, so we must avoid them. Cipher suites are cryptographic algorithms that describe how the transferred data should be encrypted.
The method you’ll use to define the ciphers depends on how you’ve configured your TLS/SSL certificates for Nginx.
If you used Certbot to obtain your certificates, it also created the file /etc/letsencrypt/options-ssl-nginx.conf which contains ciphers which aren’t strong enough for HTTP/2. Modifying this file will unfortunately prevent Certbot from applying updates in the future, so we’ll just tell Nginx not to use this file and we’ll specify our own list of ciphers.
Open the server block configuration file for your domain:

sudo nano /etc/nginx/sites-available/your_domain

Locate the line that includes the options-ssl-nginx.conf file and comment it out:
/etc/nginx/sites-available/<^>your_domain<^>

    # include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot<^>

Below that line, add this line to define the allowed ciphers:
/etc/nginx/sites-available/<^>your_domain<^>

ssl_ciphers EECDH+CHACHA20:EECDH+AES128:RSA+AES128:EECDH+AES256:RSA+AES256:EECDH+3DES:RSA+3DES:!MD5;

Save the file and exit the editor.
If you used self-signed certificates or used a certificate from a third party and configured it according to the prerequisites, open the file /etc/nginx/snippets/ssl-params.conf in your text editor:

sudo nano /etc/nginx/snippets/ssl-params.conf

Locate the following line:
/etc/nginx/snippets/ssl-params.conf

...
ssl_ciphers ECDHE-RSA-AES256-GCM-SHA512:DHE-RSA-AES256-GCM-SHA512:ECDHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-SHA384;
...

Modify it so it looks like this:
/etc/nginx/snippets/ssl-params.conf

...
ssl_ciphers EECDH+CHACHA20:EECDH+AES128:RSA+AES128:EECDH+AES256:RSA+AES256:EECDH+3DES:RSA+3DES:!MD5;

Save the file and exit your editor.
Once again, check the configuration for syntax errors:

sudo nginx -t

If you see any errors, address them and test again.
Once you see no syntax errors, restart Nginx:

sudo systemctl reload nginx

With the server restarted, let’s verify that it works.

Step 3 — Verifying that HTTP/2 is Enabled

Let’s ensure the server is running and working with HTTP/2.
Use the curl command to make a request to your site and view the headers:

curl -I -L https://your_domain

You’ll see the following output:

HTTP/1.1 301 Moved Permanently
Server: nginx/1.14.0 (Ubuntu)
Date: Fri, 06 Jul 2018 19:07:12 GMT
Content-Type: text/html
Content-Length: 194
Connection: keep-alive
Location: https://your_domain/

HTTP/2 200
server: nginx/1.14.0 (Ubuntu)
date: Fri, 06 Jul 2018 19:07:12 GMT
content-type: text/html
content-length: 16
last-modified: Fri, 06 Jul 2018 16:55:37 GMT
etag: "5b3f9f09-10"
accept-ranges: bytes

You can also verify that HTTP/2 is in use in Google Chrome. Open Chrome and navigate to http://your_domain. Open the Chrome Developer Tools (View -> Developer -> Developer Tools) and reload the page (View -> Reload This Page). Navigate to the Network tab, right-click on the table header row that starts with Name, and select the Protocol option from the popup menu.
You’ll see h2 (which stands for HTTP/2) in a new Protocol column, indicating that HTTP/2 is working.

At this point, you’re ready to serve content through the HTTP/2 protocol. Let’s improve security and performance by enabling HSTS.

Step 4 — Enabling HTTP Strict Transport Security (HSTS)

Even though your HTTP requests redirect to HTTPS, you can enable HTTP Strict Transport Security (HSTS) to avoid having to do those redirects. If the browser finds an HSTS header, it will not try to connect to the server via regular HTTP again for a given time period. No matter what, it will exchange data using only encrypted HTTPS connection. This header also protects us from protocol downgrade attacks.
Open the Nginx configuration file in your editor:

sudo nano /etc/nginx/nginx.conf

Add this line to the file to enable HSTS:
/etc/nginx/nginx.conf

http {
...
    ##
    # Virtual Host Configs
    ##

    include /etc/nginx/conf.d/*.conf;
    include /etc/nginx/sites-enabled/*;
    add_header Strict-Transport-Security "max-age=15768000" always;
}
...

The max-age is set in seconds. The value 15768000 is equivalent to 6 months.
By default, this header is not added to subdomain requests. If you have subdomains and want HSTS to apply to all of them, you should add the includeSubDomains variable at the end of the line, like this:
/etc/nginx/nginx.conf

add_header Strict-Transport-Security "max-age=15768000; includeSubDomains" always;

Save the file, and exit the editor.
Once again, check the configuration for syntax errors:

sudo nginx -t

Finally, restart the Nginx server to apply the changes.

sudo systemctl reload nginx

Conclusion

Your Nginx server is now serving HTTP/2 pages. If you want to test the strength of your SSL connection, please visit Qualys SSL Lab and run a test against your server. If everything is configured properly, you should get an A+ mark for security.