Apache reverse proxy - URL without / is refused - apache

Question

I use reverse proxy to show backend server content for a subdomain.
The subdomain.mydomain.com (server A) should display content of server with IP 123.123.123.123 port 1111 (server B).
Virtual host of subdomain.mydomain.com (server A):
<IfModule mod_ssl.c>
<VirtualHost *:443>
ServerName subdomain.mydomain.com
SSLEngine on
SecAuditEngine On
RewriteEngine On
SSLProxyEngine on
ProxyPreserveHost On
LogLevel warn
<Directory />
Options -Indexes +FollowSymLinks
AllowOverride None
Require all granted
</Directory>
<Location />
ProxyPass https://123.123.123.123:1111
ProxyPassReverse https://123.123.123.123:1111
</Location>
ErrorLog /var/log/apache2/error.log
SSLProtocol all -SSLv2 -SSLv3
SSLHonorCipherOrder on
SSLVerifyClient none
SSLVerifyDepth 1
SSLCertificateFile /etc/apache2/cert.site/chain_wildcard_site_combined.crt
SSLCertificateKeyFile /etc/apache2/cert.site/key_wildcard_site.key
SetEnvIf User-Agent ".*MSIE.*" \
nokeepalive ssl-unclean-shutdown \
downgrade-1.0 force-response-1.0
</VirtualHost>
</IfModule>
Virtual host of 123.123.123.123:1111 (server B):
<IfModule mod_ssl.c>
<VirtualHost 123.123.123.123:1111>
DocumentRoot /srv/www/site/htdocs
SSLEngine on
RewriteEngine On
SSLProxyEngine on
ProxyPreserveHost On
LogLevel warn
<Location "/">
Require ip 222.222.222.222
</Location>
<Directory />
Options FollowSymLinks
AllowOverride None
</Directory>
<Directory /srv/www/site/htdocs>
Options -Indexes +FollowSymLinks +MultiViews
DirectoryIndex index.php
AllowOverride None
Require all granted
</Directory>
ErrorLog /srv/www/site/log/error.log
CustomLog /srv/www/site/log/access.log combined
CustomLog /srv/www/site/log/ssl_request_log \
"%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x \"%r\" %b"
SSLProtocol all -SSLv2 -SSLv3
SSLHonorCipherOrder on
SSLVerifyClient none
SSLVerifyDepth 1
SSLCertificateFile /etc/apache2/cert.site/chain_wildcard_site_combined.crt
SSLCertificateKeyFile /etc/apache2/cert.site/key_wildcard_site.key
<Directory /usr/lib/cgi-bin>
SSLOptions +StdEnvVars
</Directory>
</VirtualHost>
</IfModule>
If I load URL:
https://subdomain.mydomain.com/dir/
it loads successfully.
If I load URL (without trailing slash):
https://subdomain.mydomain.com/dir
it results error page: ERR_CONNECTION_REFUSED.
EDIT1:
I execute command:
curl -IL https://subdomain.mydomain.com/dir
and I get this result:
HTTP/1.1 301 Moved Permanently
Date: Mon, 23 Aug 2021 13:45:13 GMT
Server: Apache
Strict-Transport-Security: max-age=15768000; includeSubDomains
Strict-Transport-Security: max-age=15768000; includeSubDomains
Location: https://subdomain.mydomain.com:1111/dir/
Content-Type: text/html; charset=iso-8859-1
curl: (7) Failed to connect to subdomain.mydomain.com port 1111: Connection refused
EDIT2:
I added trailing slash
<Location />
ProxyPass https://123.123.123.123:1111/
ProxyPassReverse https://123.123.123.123:1111/
</Location>
But I still get the Connection refused error.
Any idea why is it resulting error, when trailing slash is missing?
Thanks!

Answer 1

Since you used ProxyPreserveHost ON, your ProxyPassReverse should be ProxyPassReverse https://subdomain.mydomain.com:1111/ because this is the Location: header your backend is producing that you need the frontend to fixup.
The backend unfortunately sees no port in the Host: header and picks the port of the local connection. It is a problem that only happens when the default port is used on the frontend + ProxyPreserveHost. ServerName with an explicit port :443 might help on the backend.

Answer 2

You cannot use port 1111 for SSL - it MUST be 443 (modern certificates and CORS do not work or accept different ports)