Plugin development - How to access actions?
I'd suggest generating the code via pluginfactory.io and if you have code comments enabled, it'll give you the URI that you need to trigger your action in the example code.
But essentially it's going to be a kebab-case version of your controller route, with a kebab-case version of your method name (but removing the action preface).
For you, first you should rename your method thusly:
    public function actionBuu() {
        echo &quot;tradada&quot;;
    }

And then your URI would be something like:
/actions/dns-notifier/dns-notifier-controller-db-controller/buu

See here for more on controller actions