Argo Tunnel has a 1-1 relationship of tunnel to hostname. Tunnel can only accept traffic for one hostname for each instance of Tunnel. Typically if you want to run Tunnel for multiple hostnames, such as foo.example.com and bar.example.com, you need to run multiple Tunnel clients side by side.
There is one way to workaround this and run one Tunnel instance that can accept traffic across multiple hostnames, if the hostnames are on the same domain and same Level. (aka foo.example.com can be CNAME’d to bar.example.com, but not foo.com or foo.bar.example.com)
The way to do this is to start Tunnel on one hostname, then in the Cloudflare DNS editor, create CNAME records from the other hostnames you’d like to be passed back to Tunnel that point to the Tunnel’ed hostname.
For example, if you would like to run Tunnel on foo.example.com as well as bar.example.com but don’t want to run multiple instances of Tunnel, you can do: