When using the v2/groups API to update a subset of applications in a group, how does one specify the configuration for those apps that are unchanged? Does the update request have to include the full original configuration for the unchanged app, or does one simply have to include its id to indicate it is still part of the group but with configuration unchanged?
You can either
use PUT on the group and include the unchanged configuration as well. Marathon will detect which apps are changed and only redeploy changed applications.
use PUT on the app endpoint to only change one of the apps in isolation.