Subdomain not working on Apache2/Debian9 - apache

Question

I would like to set up a subdomain on my virtual server with Debian 9 and Apache 2 which points to a directory at /var/www/html/test.
SSL and Let's Encrypt is also enabled, so the subdomain should be reached with https too.
My 000-default.conf file looks like:
<VirtualHost _default_:80>
ServerAdmin webmaster#localhost
DocumentRoot /var/www/html
ErrorLog ${APACHE_LOG_DIR}/error.log
CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>
# vim: syntax=apache ts=4 sw=4 sts=4 sr noet
<VirtualHost _default_:443>
DocumentRoot /var/www/html
ServerName www.example.com
<IfModule mod_headers.c>
Header always set Strict-Transport-Security "max-age=15768000; includeSubDomains; preload"
</IfModule>
SSLEngine on
ServerAlias www.example.com
SSLCertificateFile /etc/letsencrypt/live/www.example.com/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/www.example.com/privkey.pem
Include /etc/letsencrypt/options-ssl-apache.conf
</VirtualHost>
The file default-ssl.conf looks like:
<IfModule mod_ssl.c>
<VirtualHost *:443>
ServerAdmin webmaster#localhost
DocumentRoot /var/www/html
SSLCertificateFile /etc/letsencrypt/live/example.com/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/example.com/privkey.pem
ErrorLog ${APACHE_LOG_DIR}/error.log
CustomLog ${APACHE_LOG_DIR}/access.log combined
SSLEngine on
<FilesMatch "\.(cgi|shtml|phtml|php)$">
SSLOptions +StdEnvVars
</FilesMatch>
<Directory /usr/lib/cgi-bin>
SSLOptions +StdEnvVars
</Directory>
ServerName www.example.com
ServerAlias example.com
</VirtualHost>
</IfModule>
# vim: syntax=apache ts=4 sw=4 sts=4 sr noet
I made a new copy of the 000-default.conf file, named it "test.example.com.conf" and enabled it by means of a2ensite. The file looks like:
<VirtualHost _default_:80>
ServerAdmin webmaster#test.example.com
DocumentRoot /var/www/html/test
ErrorLog ${APACHE_LOG_DIR}/error.log
CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>
# vim: syntax=apache ts=4 sw=4 sts=4 sr noet
<VirtualHost _default_:443>
DocumentRoot /var/www/html/test
ServerName test.example.com
<IfModule mod_headers.c>
Header always set Strict-Transport-Security "max-age=15768000; includeSubDomains; preload"
</IfModule>
SSLEngine on
ServerAlias test.example.com
SSLCertificateFile /etc/letsencrypt/live/www.example.com/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/www.example.com/privkey.pem
Include /etc/letsencrypt/options-ssl-apache.conf
</VirtualHost>
My hosts file includes the entry SERVER_IP_ADDRESS test.example.com.
The DNS server has an "A"-Entry with test.example.com pointing on SERVER_IP_ADDRESS.
Pinging test.example.com from another machine ends in "Host not found" and a ping on the virtual server results in an response from itself.
So why does the webbrowser only show "Server not found"?
Did I forget something? Is something in my config wrong?

Answer 1

After long testing and research I found the mistake!
There were 3:
The DNS A-entry took some time to complete
my .htaccess forwarding caused the URL always to be rewritten to www.example.com, no matter which subdomain was typed in
my test.example.com.conf file has a mistake in it which makes the subdomain only available via https: the ServerAlias instruction was missing inside <VirtualHost _default_:80>
So it works so far and needs some improvements...
I hope I will help someone else with my mistakes!