Second subdomain ignores DirectoryIndex and uses default domain index file

Question

I'm running an apache2 web server that came pre-installed on debian. Apache configuration hosts file is:

<VirtualHost *:80>
    ServerName domain.com
    ServerAlias www.domain.com
    DocumentRoot /var/www/html

    ErrorLog ${APACHE_LOG_DIR}/error.log
    CustomLog ${APACHE_LOG_DIR}/error.log combined
</VirtualHost>
<VirtualHost *:80>
    ServerName sub1.domain.com
    ServerAlias www.sub1.domain.com
    DocumentRoot /var/www/sub1/public_html
    DirectoryIndex sub1.php

    ErrorLog ${APACHE_LOG_DIR}/error.log
    CustomLog ${APACHE_LOG_DIR}/error.log combined
</VirtualHost>
<VirtualHost *:80>
    ServerName sub2.domain.com
    ServerAlias www.sub2.domain.com
    DocumentRoot /var/www/sub2/public_html
    DirectoryIndex sub2.php

    ErrorLog ${APACHE_LOG_DIR}/error.log
    CustomLog ${APACHE_LOG_DIR}/error.log combined
</VirtualHost>

apachectl -S output:

VirtualHost configuration:
*:80                   is a NameVirtualHost
         default server domain.com (/etc/apache2/sites-enabled/domain.com.conf:1)
         port 80 namevhost domain.com (/etc/apache2/sites-enabled/domain.com.conf:1)
                 alias www.domain.com
         port 80 namevhost sub1.domain.com (/etc/apache2/sites-enabled/domain.com.conf:10)
                 alias www.sub1.domain.com
         port 80 namevhost sub2.domain.com (/etc/apache2/sites-enabled/domain.com.conf:19)
                 alias www.sub2.domain.com
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

domain.com loads the default index.html file that came pre-installed at /var/www/html/index.html (Intended)

sub1.domain.com loads sub1.php. (Intended)

sub2.domain.com loads the default index file at /var/www/html/index.html. I can access the intended file, sub2.php, as a directory: sub2.domain.com/sub2.php

How can I make my second subdomain obey the DirectoryIndex directive, and load sub2.php my navigating to sub2.domain.com?

Answer 1

I don't know what changed, but this morning (the day after posting this question) it is now loading the DirectoryIndex as intended.

This is probably a bug in Apache, specifically how it handles a changed DirectoryIndex when you reload. For posterity, I'm using systemd to reload the apache configuration.