I've read countless questions and answers almost identical to my problem but cannot figure this out. Environment is Apache 2.4.6 on CentOS 7.4.

I have my nameserver records with DO:
A jenks.nz points to my droplet
CNAME www points to jenks.nz

Either of those addresses loads my site. If I use the www prefix, then that domain remains in my browser location bar. If I use the one without www then the location switches to the IP address.

My virtual host config is as follows:

<VirtualHost *:80>
    ServerName jenks.nz
    ServerAlias www.jenks.nz
    DocumentRoot /var/www/jenks.nz/public_html
    ErrorLog /var/log/httpd/jenks.nz.error.log
    CustomLog /var/log/httpd/jenks.nz.requests.log combined
</VirtualHost>

I originally had the ServerName and ServerAlias around the other way but the result was the same.

At this stage I have a simple, static HTML page for testing. There's a WordPress install waiting in the wings, and I know about the settings there (because I've stuffed them up on several occasions before on shared hosts :-) ). I've verified there is no .htaccess file in the document root for this virtual host.

I'm sure I'm missing something simple, but I cannot figure out what.