The Debian package of the alertmanager does not include a web application.
Please, use the amtool command-line application to obtain
equivalent functionality.
Alternatively, you can deploy your own files to be served by the
embedded web server, by placing them in
/usr/share/prometheus/alertmanager/ui/, or by using the
--web.local-assets option to point to a different path. Note
that the web server will only serve files in the lib and
app sub-directories.
You can still use the HTTP API, and the special handlers: