Introduction: Trying to add a node to a cluster and receiving an error along with the status of the node showing pending in the UCP UI
Introduction: Most likely what has happened is the engine ids have been duplicated, prior to joining the UCP Swarm cluster. In most cases this is a consequence of cloning VMs with the engine already installed. The engine id is generated on Docker's first run and stored in /etc/docker/key.json. When creating a VM template, make sure /etc/docker/key.json is not included in the image.
To recover the existing installation, remove /etc/docker/key.json and restart docker on each node.