On June 30, 2016 this issue was created on GitHub to request the implementation of static IP on docker-swarm services.
Since then multiple replies with thumbs up and down were added.
At the time of writing on December 20, 2019 this issue is open and the feature has not been implemented.
Discussion
After reading all comments I strongly doubt whether static IPs will everyever be implemented in docker-swarm. On the other hand it is unclear why this issue has not been closed. If people would like to see that this feature gets implemented, one could create a Pull request or add a thumbs up to create more awareness.