Apache points to wrong vhost conf file - linux

Question

I have a fresh VPS on Ubuntu 18. Have installed only PHP and Apache. Created only a one vhost config:
<VirtualHost *:80>
ServerName vp123.ovh.net
DocumentRoot /var/www/app
</VirtualHost>
After apache realod, the domain is pointing to default folder /var/www/html instead of my /var/www/app
000-default.conf is default:
<VirtualHost *:80>
# The ServerName directive sets the request scheme, hostname and port that
# the server uses to identify itself. This is used when creating
# redirection URLs. In the context of virtual hosts, the ServerName
# specifies what hostname must appear in the request's Host: header to
# match this virtual host. For the default virtual host (this file) this
# value is not decisive as it is used as a last resort host regardless.
# However, you must set it for any further virtual host explicitly.
#ServerName www.example.com
ServerAdmin webmaster#localhost
DocumentRoot /var/www/html
# Available loglevels: trace8, ..., trace1, debug, info, notice, warn,
# error, crit, alert, emerg.
# It is also possible to configure the loglevel for particular
# modules, e.g.
#LogLevel info ssl:warn
ErrorLog ${APACHE_LOG_DIR}/error.log
CustomLog ${APACHE_LOG_DIR}/access.log combined
# For most configuration files from conf-available/, which are
# enabled or disabled at a global level, it is possible to
# include a line for only one particular virtual host. For example the
# following line enables the CGI configuration for this host only
# after it has been globally disabled with "a2disconf".
#Include conf-available/serve-cgi-bin.conf
</VirtualHost>
apache2ctl -S outputs:
VirtualHost configuration:
*:80 is a NameVirtualHost
default server vp123.ovh.net (/etc/apache2/sites-enabled/000-default.conf:1)
port 80 namevhost vp123.ovh.net (/etc/apache2/sites-enabled/000-default.conf:1)
port 80 namevhost vp123.ovh.net (/etc/apache2/sites-enabled/vp123.ovh.net.conf:1)
ServerRoot: "/etc/apache2"
Main DocumentRoot: "/var/www/html"
Main ErrorLog: "/var/log/apache2/error.log"
Mutex default: dir="/var/run/apache2/" mechanism=default
Mutex mpm-accept: using_defaults
Mutex watchdog-callback: using_defaults
PidFile: "/var/run/apache2/apache2.pid"
Define: DUMP_VHOSTS
Define: DUMP_RUN_CFG
User: name="www-data" id=33
Group: name="www-data" id=33
When pointing a new domain to this server - works perfect. But this "default domain" is always pointing to default folder. Disabling 000-default.conf helps but I don't want do that.

Answer 1

The virtual host defined at 000-default.conf doesn't have a ServerName directive so it inherits the value from its parent container (in this case the main server settings) and I presume such directive also has vp123.ovh.net as value. Thus Apache considers the first virtual host matches.
A ServerName should be specified inside each <VirtualHost> block. If it is absent, the ServerName from the "main" server configuration will be inherited.
Since you want to use that name elsewhere a possible solution is to set a explicit value that doesn't interfere, e.g.:
<VirtualHost *:80>
ServerName localhost
DocumentRoot /var/www/html
</VirtualHost>

Answer 2

Apache selects the virtual host as described in the documentation.
Considering the vhost selection process your options are:
Disable the default vHost, you don't need it.
Really. Why would you want to keep it?
Change the default vHost declaration to <VirtualHost *>. Therefore making the other vHost the default for requests targeted at port 80.
Add your servers ip address to your vhost declaration. (<VirtualHost 1.2.3.4:80>) It will then take precedence over the default vhost *:80 for requests targeted at that IP-address. Note that requests to other to other IPs of your server will still be served by the *:80-vHost.
Set DocumentRoot /var/www/app inside your default vHost. This will require you to make configuration changes in multiple vHost each time and thus increases the chance of making mistakes.