Apache Proxy: No protocol handler was valid

Question

I am trying to proxy a subdirectory to another server. My httpd.conf:

RewriteEngine On
ProxyPreserveHost On
RewriteRule .*subdir/ https://anotherserver/subdir/ [P]

The problem is that Apache is always logging this:

AH01144: No protocol handler was valid for the URL /subdir/. If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule., referer: http://localhost/

So after searching the internet, I have activated these modules:

LoadModule headers_module modules/mod_headers.so
LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_ajp_module modules/mod_proxy_ajp.so
LoadModule proxy_connect_module modules/mod_proxy_connect.so
LoadModule proxy_express_module modules/mod_proxy_express.so
LoadModule proxy_fcgi_module modules/mod_proxy_fcgi.so
LoadModule proxy_ftp_module modules/mod_proxy_ftp.so
LoadModule proxy_html_module modules/mod_proxy_html.so
LoadModule proxy_http_module modules/mod_proxy_http.so
LoadModule proxy_scgi_module modules/mod_proxy_scgi.so
LoadModule proxy_wstunnel_module modules/mod_proxy_wstunnel.so
LoadModule rewrite_module modules/mod_rewrite.so

(I know that I don't need all of them but I just activated them to be sure I am not missing one)

But this error still appears and clients get a HTTP 500.

How can I fix this?

Answer 1

This can happen if you don't have mod_proxy_http enabled

sudo a2enmod proxy_http

For me to get my https based load balancer working, i had to enable the following:

sudo a2enmod ssl
sudo a2enmod proxy
sudo a2enmod proxy_balancer
sudo a2enmod proxy_http