Currently, in order for a Deployment to rollback:
i. a user needs to set d.spec.rollbackTo.revision
ii. the controller notices the populated rollback spec and it updates the pod template of the deployment plus it cleans up the rollbackTo field.

Step ii. is breaking the declarative model for the Deployment API. We should consider dropping rollbackTo from the spec and instead either 1. make the deployments/{name}/rollback endpoint perform the rollback or 2. have the rollback endpoint simply return a dry-run of the rolled back Deployment which then clients can PUT.

If we do 1. we need an option for dry-run, 2. is what we do in OpenShift.

@kubernetes/sig-apps-api-reviews

ps. sparked by the decision to have rollback client-side initially for DaemonSets and StatefulSets.