I need to communicate the IPaddress of my Mendix app for whitelisting, so that I can consume a webservice. I have got the outbound IP ranges of Mendix cloud v3, but the other party does not accept that, because they want to make sure that it is only my app that is sending requests. Am I right in thinking that my app does not have it's own outbound IP, only a shared range (because it is behind NAT?)? Is there a way to resolve this issue?
You can find the Mendix IP addresses here: https://docs.mendix.com/developerportal/deploy/mendix-ip-addresses#2-definitions
They are subject to potential change, but Mendix should give you 48 hours notice if this is going to happen.
As you said it’s a shared range, but I think it’s the best you’ll get at the moment.
I think you are right that you can’t get a single IP address for your app (I would check with support to confirm because this is v3, and could be a different case). Is it possible to change the authentication method of the web service that you are using? Maybe use a client certificate or JWT? Another option you can look into sine you are on v3 is a vpn connection, the documentation says its deprecated but I remember that was possible in v3.