How to Configure mod_http2 with Apache on AlmaLinux

The HTTP/2 protocol is the modern standard for faster and more efficient communication between web servers and clients. It significantly improves web performance with features like multiplexing, header compression, and server push. Configuring mod_http2 on Apache for AlmaLinux allows you to harness these benefits while staying up to date with industry standards.

This detailed guide will walk you through the steps to enable and configure mod_http2 with Apache on AlmaLinux, ensuring your server delivers optimized performance.

Prerequisites

Before proceeding, ensure you have the following:

1. AlmaLinux 8 or later installed on your server.
2. Apache web server (httpd) installed and running.
3. SSL/TLS certificates (e.g., from Let’s Encrypt) configured on your server, as HTTP/2 requires HTTPS.
4. Basic knowledge of Linux commands and terminal usage.

Step 1: Update the System and Apache

Keeping your system and software updated ensures stability and security. Update all packages with the following commands:

sudo dnf update -y
sudo dnf install httpd -y

After updating Apache, check its version:

httpd -v

Ensure you’re using Apache version 2.4.17 or later, as HTTP/2 support was introduced in this version. AlmaLinux’s default repositories provide a compatible version.

Step 2: Enable Required Modules

Apache requires specific modules for HTTP/2 functionality. These modules include:

1. mod_http2: Implements the HTTP/2 protocol.
2. mod_ssl: Enables SSL/TLS, which is mandatory for HTTP/2.

Enable these modules using the following commands:

sudo dnf install mod_http2 mod_ssl -y

Verify that the modules are installed and loaded:

httpd -M | grep http2
httpd -M | grep ssl

If they’re not enabled, load them by editing the Apache configuration file.

Step 3: Configure mod_http2 in Apache

To enable HTTP/2 globally or for specific virtual hosts, you need to modify Apache’s configuration files.

1. Edit the Main Configuration File

   Open the main Apache configuration file:

   sudo nano /etc/httpd/conf/httpd.conf
   

   Add or modify the following lines to enable HTTP/2:

   LoadModule http2_module modules/mod_http2.so
   Protocols h2 h2c http/1.1
   

   • h2: Enables HTTP/2 over HTTPS.
   • h2c: Enables HTTP/2 over plain TCP (rarely used; optional).

2. Edit the SSL Configuration

   HTTP/2 requires HTTPS, so update the SSL configuration:

   sudo nano /etc/httpd/conf.d/ssl.conf
   

   Add the Protocols directive to the SSL virtual host section:

   <VirtualHost *:443>
       Protocols h2 http/1.1
       SSLEngine on
       SSLCertificateFile /path/to/certificate.crt
       SSLCertificateKeyFile /path/to/private.key
       ...
   </VirtualHost>
   

   Replace /path/to/certificate.crt and /path/to/private.key with the paths to your SSL certificate and private key.

3. Save and Exit
   Press Ctrl+O to save the file, then Ctrl+X to exit.

Step 4: Restart Apache

Restart Apache to apply the changes:

sudo systemctl restart httpd

Verify that the service is running without errors:

sudo systemctl status httpd

Step 5: Verify HTTP/2 Configuration

After enabling HTTP/2, you should verify that your server is using the protocol. There are several ways to do this:

1. Using curl

   Run the following command to test the HTTP/2 connection:

   curl -I --http2 -k https://your-domain.com
   

   Look for the HTTP/2 in the output. If successful, you’ll see something like this:

   HTTP/2 200
   

2. Using Browser Developer Tools

   Open your website in a browser like Chrome or Firefox. Then:

   • Open the Developer Tools (right-click > Inspect or press F12).
   • Navigate to the Network tab.
   • Reload the page and check the Protocol column. It should show h2 for HTTP/2.

3. Online HTTP/2 Testing Tools

   Use tools like KeyCDN’s HTTP/2 Test to verify your configuration.

Step 6: Optimize HTTP/2 Configuration (Optional)

To fine-tune HTTP/2 performance, you can adjust several Apache directives.

1. Adjust Maximum Concurrent Streams

   Control the maximum number of concurrent streams per connection by adding the following directive to your configuration:

   H2MaxSessionStreams 100
   

   The default is usually sufficient, but for high-traffic sites, increasing this value can improve performance.

2. Enable Server Push

   HTTP/2 Server Push allows Apache to proactively send resources to the client. Enable it by adding:

   H2Push on
   

   For example, to push CSS and JS files, use:

   <Location />
       Header add Link "</styles.css>; rel=preload; as=style"
       Header add Link "</script.js>; rel=preload; as=script"
   </Location>
   

3. Enable Compression

   Use mod_deflate to compress content, which works well with HTTP/2:

   AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css application/javascript
   

4. Prioritize HTTPS

   Ensure your site redirects all HTTP traffic to HTTPS to fully utilize HTTP/2:

   <VirtualHost *:80>
       ServerName your-domain.com
       Redirect permanent / https://your-domain.com/
   </VirtualHost>
   

Troubleshooting HTTP/2 Issues

If HTTP/2 isn’t working as expected, check the following:

1. Apache Logs Review the error logs for any configuration issues:

   sudo tail -f /var/log/httpd/error_log
   

2. OpenSSL Version HTTP/2 requires OpenSSL 1.0.2 or later. Check your OpenSSL version:

   openssl version
   

   If it’s outdated, upgrade to a newer version.

3. Firewall Rules Ensure ports 80 (HTTP) and 443 (HTTPS) are open:

   sudo firewall-cmd --add-service=http --permanent
   sudo firewall-cmd --add-service=https --permanent
   sudo firewall-cmd --reload
   

Conclusion

Configuring mod_http2 with Apache on AlmaLinux enhances your server’s performance and provides a better user experience by utilizing the modern HTTP/2 protocol. With multiplexing, server push, and improved security, HTTP/2 is a must-have for websites aiming for speed and efficiency.

By following this guide, you’ve not only enabled HTTP/2 on your AlmaLinux server but also optimized its configuration for maximum performance. Take the final step to test your setup and enjoy the benefits of a modern, efficient web server.

For any questions or further clarification, feel free to leave a comment below!