Docker Universal Control Plane install fails with "unable to verify that no UCP components already exist"

You may hit this error if you have had a failed attempt at deploying the UCP and there is still orphaned references to it on the Docker host. I forgot to remove the old UCP Docker volumes so when I tried to deploy the latest verion of UCP this happened.

"FATA[0001] unable to verify that no UCP components already exist: the following volumes appear to be from an existing UCP installation and must be removed before proceeding with a new in                stallation: ucp-kv ucp-metrics-data ucp-auth-api-certs ucp-auth-store-certs ucp-client-root-c                a ucp-cluster-root-ca ucp-controller-server-certs ucp-auth-worker-certs ucp-auth-worker-data          
    ucp-kv-certs ucp-auth-store-data ucp-controller-client-certs ucp-node-certs"

Simply use the docker volume prune command to get rid of all the old volumes which are not associated to a running container. Tread with caution if you are using a production system.

How to create a new Docker Swarm on Debian-Buster10

A Docker Swarm is a collection of node working together in a cluster. A Swarm can be made up of manager and worker node. As with most clustering solutions the recommendation is to try and avoid having an even number of nodes, to prevent issues with voting rights and cluster quorum. 

The diagram depicts how a Docker Swarm looks. 

The command below should be run on the first node which you want to become a Swarm Manager, its possible (and recommended) to have more than one Swarm Manager. However, when you initialise the cluster the first node becomes the "manager leader" which is basically the node which conducts and manages the orchestration tasks of the cluster.

docker swarm init --advertise-addr "pirate ip of cluster manager node"

The -advertise-addr switch tells the cluster to be provisioned with the correct address. In many examples its possible to leave this out and the docker swarm command assumes the private address of the host anyway. It's more important to be explicit if the host belongs to multiple networks, perhaps in a public cloud provider where the node might have multiple interfaces on different network segments. 

The following command can be run to check to see if the cluster has provisioned correctly. 

docker node ls

After running the docker swarm init command, it will generate string which can be used to join worker nodes to your Swarm cluster.