When trying to add a node to a cluster, the following error occurs with the status of the node showing pending in the UCP UI:
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 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.