docker-docs/docs/reference/create.md

create — Create a discovery token

The create command uses Docker Hub's hosted discovery backend to create a unique discovery token for your cluster. For example:

$ docker run --rm  swarm create
86222732d62b6868d441d430aee4f055

Later, when you use manage or join to create Swarm managers and nodes, you use the discovery token in the <discovery> argument (e.g., token://86222732d62b6868d441d430aee4f055). The discovery backend registers each new Swarm manager and node that uses the token as a member of your cluster.

Some documentation also refers to the discovery token as a cluster_id.

Warning: Docker Hub's hosted discovery backend is not recommended for production use. It’s intended only for testing/development.

For more information and examples about this and other discovery backends, see the Docker Swarm Discovery topic.