Graylog web interface not reachable

Hello team!

I have a probleme reaching my Graylog web interface, here is my Graylog configuration:

http_bind_address = 0.0.0.0:9000
http_publish_uri = http://172.X.X.X:9000/
http_external_uri = http://172.X.X.X:9000/

So i understand that:

http_publish_uri is where each Graylog connects to itself and in a cluster all other nodes connect to this.
http_external_uri is where your browser can reach Graylog.

The thing is, when i put the IP adress in http_external_uri and type the IP adress in my browser it works, i can reach the graylog interface.
BUT when i put http://domainename.com/ in the http_external_uri and type http://domainename.com in my browser it doesn’t work.

My goal here would be to be able to reach graylog web interface with http://domainname.com/. My understanding is that it should work by changing the http_external_uri. So can it be a probleme in my graylog configuration or is it sure that the probleme comes from outside of graylog configuration?

Thanks!

the question is, does domainename.com resolve to 172.X.X.X or something different?