Last updated: 15 Feb 2018

Apache version 2.4.17 introduced HTTP/2 support. If your server is running Apache version below this version, you need to upgrade Apache to the latest version first.

To install the packages required, simply run as root: # yum install httpd modssl -y If the server already have httpd installed, you only need to install modssl, all the required configuration is done by the installer. Note however that in this case you need to restart httpd, so it can load the ssl module. I'm not sure why everyone is harshing on your answer; it correctly describes why one will not find the a2enmod scripts in Red Hat-alikes. Personally, my plan is to use puppet to manage a similar layout on my RHEL boxes. – Chad Huneycutt Aug 20 '09 at 2:09. This manual page documents briefly the a2enmod and a2dismod commands. A2enmod is a script that enables the specified module within the apache2 configuration.

Upgrade Apache

Depending on the server operating system, you may be able to download the compiled latest version.

Windows

You can either compile Apache yourself, or download compiled Windows binaries. We recommend Apache Lounge builds.

Ubuntu / Debain

Apache web server distributed in default software repositories of Ubuntu and Debian do not include mod_http2 needed to enable HTTP/2 functionality. You will need to add a third-party package source with latest Apache version that also inludes mod_http2.

This will install some utilities (if not installed already) that help us add external PPAs. Secondly, we add theondrej/apache2 PPA which contains the latest Apache2builds. Third, we update your systems package information.This is to upgrade your existing Apache2 version to the latest version. After upgrading, the apachectl -vcommand will reveal your upgraded Apache version. This will be 2.4.29 or later.

CentOS / RHEL

Both CentOS and RHEL default repositories come with Apache versions around 2.4.6. Apache official web sitehas information about building the latest Apache server.

Enable HTTP/2 module

Apache's HTTP/2 support comes from the mod_http2 module. Enable it from:If above commands do not work in your system (which is likely the case in CentOS/RHEL), use LoadModuledirective in httpd configuration directory to enable http2 module.

Add HTTP/2 Support

We highly recommend you enable HTTPS support for your web site first. Most web browser simply do not support HTTP/2 overplain text. Besides, there are no excuses to not use HTTPS anymore.HTTP/2 can be enabled site-by-site basis. Locate your web site's Apache virtual host configuration file, and add the followingright after the opening <VirtualHost> tag:Overall, your configuration file should look something like this:After the changes, don't forget to reload/restart Apache.

Push resources

Apache supports HTTP/2 Push feature as well. After enabling Apache HTTP/2, you can add push support simply by settingHTTP Link headers. You can emit them from either/both the Apache configuration file, or from your application.Above is an example header that would trigger Apache to push the /assets/styles.css and/assets/scripts.scc files. Refer to your application code on how to emit HTTP headers.If you would like to make Apache add these headers, you can do so like this, using the mod_headers module.Above example demonstrates Apache configuration that sets 2 Link headers (you can have as many as you need).Supported browsers will decide to preload these resources if necessary.

Troubleshooting

Apache 2.4.27, HTTP/2 not supported in prefork

Starting from Apache 2.4.27, the Apache MPM (Multi-Processing Module) prefork no longer supports HTTP/2. This will be indicated in your Apache error log as follows:
To fix this, select a different MPM: event or worker. We highly recommend you to use the event prefork.
If you are using PHP, it is likely that PHP is integrated to Apache via the

VirtualBox Guest Addition Installation

mod_php module, which requires the prefork MPM. If you switch out from preform MPM, you will need to use PHP as FastCGI. To switch to php-fpm, you can do as folllwing. Please note that this assumes you have PHP installed from ondrej/php repository on Ubuntu. The PHP package names could be different in other repositories. Change package name and apt-get commands to match your PHP vendor and package manager.

Chapter 2. The Apache HTTP Server Red Hat Enterprise Linux 6 ...

HTTP/2 not enabled on older TLS versions

Mozilla Firefox (among other browsers) does not enable HTTP/2 protocol unless the connection is made over TLS 1.2 andusing modern cipher suits. This is not a technical limitation, but rather a safety precaution. Make sure your that yoursite supports TLS 1.2, and modern cipher suits with AES/CHACHA20 with forward-secrecy key exchanges. In turn, Apachedoes not try to establish an HTTP/2 connection with connections over older cipher configurations either. you can forceApache attempt HTTP/2 upgrade with the following directive, but it will not be as effective because browsers do notsupport HTTP/2 from their end anyway.

HTTP 421: Misdirected Request errors

HTTP/2 is designed to make parralel requests to the server over the same session. If two connections use same TLScertificate and remote IP address, browsers will attempt to reuse an existing connection. Apache can correctly servesuch requests even if those requests belong to different Virtual Hosts. However, if you have different TLS configuration(protocol, client verification, or cipher suits), Apache will reject such requests with an HTTP 421: Misdirected Request error.To prevent this, make sure you keep same TLS settings for all Virtual Hosts that you serve a particular site in.

Foot notes

Reported mod_http2-related security vulnerabilities are as follows.