Comments on How to Enable HTTP/2 in Apache Web Server on Ubuntu and Debian

Important information missing. The default MPM prefork module is not sufficient and will lead to error message:

"AH10034: The mpm module (prefork.c) is not supported by mod_http2. The mpm determines how things are processed in your server. HTTP/2 has more demands in this regard and the currently selected mpm will just not do."

One needs to install an MPM like mpm_event that is multithreaded. And this again causes mod_php to not work safely anymore, as it is not thread-safe. So if you run PHP, and most people will do, you need to run PHP through php-fpm and that means having another additinal daemon running on the server.

All of this is no big issue, but needs to be mentioned or people will be misled.

This is exactly what i am facing! Great Work Daniel!

I finally found definitve solution. (refer https://http2.pro/doc/Apache )

Here is direct Ctrl+C and Ctrl+V | I am lazy ;) |

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:

AH10034: The mpm module (prefork.c) is not supported by mod_http2. The mpm determines how things are processed in your server. HTTP/2 has more demands in this regard and the currently selected mpm will just not do. This is an advisory warning. Your server will continue to work, but the HTTP/2 protocol will be inactive.

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 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. 

apachectl stop apt-get install php7.1-fpm # Install the php-fpm from your PHP repository. This package name depends on the vendor. a2enmod proxy_fcgi setenvif a2enconf php7.1-fpm # Again, this depends on your PHP vendor. a2dismod php7.1 # This disables mod_php. a2dismod mpm_prefork # This disables the prefork MPM. Only one MPM can run at a time. a2enmod mpm_event # Enable event MPM. You could also enable mpm_worker. apachectl start 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 and using modern cipher suits. This is not a technical limitation, but rather a safety precaution. Make sure your that your site supports TLS 1.2, and modern cipher suits with AES/CHACHA20 with forward-secrecy key exchanges. In turn, Apache does not try to establish an HTTP/2 connection with connections over older cipher configurations either. you can force Apache attempt HTTP/2 upgrade with the following directive, but it will not be as effective because browsers do not support HTTP/2 from their end anyway.

H2ModernTLSOnly off

Could not change  HTTP/1.1  to HTTP/2.0 

Hello! I folowed this tutorial to enable http2 on my website , however if I check with online tools it still says I am not using http2 ? I restarted apache2 after configuring everything. Any ideas?

What happen if a browser force to get a http/1.1 request in a http/2 server? The webpage will not be display. What is the solution?

Adding the Protocols to the apache2.conf solves your question.

Protocols h2 http/1.1

this tutorial worked for me on debian 10 using ispconfig control panel Version: 3.1.15p3.I did not edit the vhost file or other apache2 config file.I did enable spdy/http2 in the ispconfig admin panel unde Server Config>Web>SSL Makes SPDY/HTTP2 available check. And then enable in the website at the bottom of the ssl tab (in the client dashboard in my case).I rebooted the server and then it worked.