Before v0.21.0 I used to be able to do:

$ kn service update echo --image duglin/echo

and it would always force a new revision to be created. This was really handy when all I wanted was for the image to be re-downloaded because I did a "docker build" to update it. Notice, I don't have a tag on the image name.

It would be nice if this feature was added back in. W/o it, it's not clear to me how to force this to happen.... at least not w/o some (non-obvious to a newbie) hack, like specifying a revision name or adding --env foo=$RANDOM to the cmd line.