Ok, I was able resolve the problem this morning. When I was seeing the problem in Ambari I was logged in as 'admin' user. It turns out that there was another user account which opened the 'add service' dialog (but had not begun any installation) and closed the browser window without exiting out of the dialog. By logging into that second account and closing the dialog I was able to interact with the cluster normally again. It would've been nice if the system automatically cancelled the 'add service' dialog when the second users session had expired, or at least listed which user had initiated the action. As no installation had begun it just sat there waiting for user input for days, while also locking all other users out from making changes. ... View more