How to Enable HTTP/2 on Your Site

1. Check versions: nginx -V (≥ 1.9.5), openssl version (≥ 1.0.2 for ALPN)
2. In nginx replace listen 443 ssl; with listen 443 ssl http2;
3. Apache: a2enmod http2 + add Protocols h2 http/1.1 to vhost
4. Syntax check: nginx -t / apachectl configtest
5. Reload: systemctl reload nginx / systemctl reload apache2
6. Verify via Enterno SSL/TLS Checker — ALPN will show h2
7. Or in shell: curl -I --http2 https://example.com

• HTTP/2 works ONLY over HTTPS — browsers do not support HTTP/2 cleartext
• OpenSSL older than 1.0.2 (CentOS 6, Ubuntu 14.04) lacks ALPN → HTTP/2 unavailable
• Apache prefork MPM is incompatible with mod_http2 — switch to event MPM
• HTTP/1.1 browser connection pooling can be faster for some workloads — always measure

To enable HTTP/2 in Nginx and Apache, you need to ensure your server supports it and then modify the configuration files. For Nginx, use the directive http2 in your server block. For Apache, enable the mod_http2 module and add Protocols h2 http/1.1 to your VirtualHost. Don't forget to ensure you are using SSL, as HTTP/2 requires HTTPS.

To enable HTTP/2 in Nginx, follow these steps:

1. Check Nginx Version: Ensure you are running Nginx version 1.9.5 or higher, as HTTP/2 support was introduced in this version. You can check your version using the command:

nginx -v

1. Update Configuration: Open your Nginx configuration file, typically located at /etc/nginx/nginx.conf or within the /etc/nginx/sites-available/ directory for site-specific configurations. In the server block where you have SSL enabled, modify the listen directive to include http2:

server {
    listen 443 ssl http2;
    server_name example.com;

    ssl_certificate /path/to/certificate.crt;
    ssl_certificate_key /path/to/privatekey.key;

    location / {
        # Your location settings
    }
}

1. Test Configuration: Before applying changes, test the Nginx configuration for any syntax errors:

nginx -t

1. Restart Nginx: If the test is successful, restart Nginx to apply the new configuration:

systemctl restart nginx

1. Verify HTTP/2: You can verify if HTTP/2 is enabled using online tools or by inspecting the response headers with cURL:

curl -I -s --http2 https://example.com | grep HTTP/2

If you see HTTP/2 200, HTTP/2 is successfully enabled.

To enable HTTP/2 in Apache, follow these detailed steps:

1. Check Apache Version: You need Apache version 2.4.17 or higher. Check your version with:

apache2 -v

1. Enable Required Modules: Ensure the mod_http2 module is enabled. You can enable it using the following command:

a2enmod http2

1. Update VirtualHost Configuration: Edit your Apache configuration file (typically in /etc/httpd/conf/httpd.conf or /etc/apache2/sites-available/ for site-specific configurations). Add the following lines to your VirtualHost section that uses SSL:

<VirtualHost *:443>
    ServerName example.com
    DocumentRoot /var/www/html

    SSLEngine on
    SSLCertificateFile /path/to/certificate.crt
    SSLCertificateKeyFile /path/to/privatekey.key

    Protocols h2 http/1.1
</VirtualHost>

1. Test Configuration: Always test your Apache configuration after making changes:

apachectl configtest

1. Restart Apache: If the test is successful, restart Apache to apply the changes:

systemctl restart apache2

1. Verify HTTP/2: Similar to Nginx, verify HTTP/2 is working using cURL:

curl -I -s --http2 https://example.com | grep HTTP/2

Seeing HTTP/2 200 confirms that HTTP/2 is enabled on your Apache server.