Roaming/floating style IP's on the network, not associated with a host, only service

How to best approach this networking problem.

I remember solving this years ago but can’t seem to find the solution.
What I need is a reserved IP address not attached to a node or host but a service.
Since I’m running a swarm I expect the IP to be bound to the service wherever the service is placed, as well as follow if the service is moved.

I can’t seem to figure out how to formulate a search that gets me relevant answers.

Oh, and I expect to replace nodes often, so no node-IP can be reserved for this.

I feel it should be easy, but I can’t see how from documentation or other material.

Any pointers?