I have been searching online for anyone to have mentioned this ever so slightly, but I can't seem to find the -i option when running docker service create. I am not sure if this is a deprecated feature, but you can do the following docker run -it, and when running docker inspect, you can see that the container Tty and OpenStdin are set to true. docker service create documentation only has -t, but missing its -i. Nothing saying this feature is being deprecated, or maybe it's simply forgotten.

In other words, how should one enable OpenStdin when running from docker service create?