Open
Description
Right now, if an innocuous update that result in no change is encountered, the user receives no feedback that the change will not trigger the update. A common case would be encountered when updating an image:
$ docker service create --name foo redis
$ docker service update --image redisIn this case, even though the update is issued, no new tasks will be dispatched since the image name did not actually change. We can mitigate this by looking up the image hash client-side, but there are other parameters that may not result in an update.
The output should make it clear whether or not there will be updates based on the changes:
$ docker service update --image redis
No changes to service detected