According to the document on the official website of rancher 2.4, only one Linux host is required. Remember that a single node rancher server can be quickly deployed. Of course, this can only be used for testing. Deployment is very convenient. Just start dcoker on the host, and then start a container:

sudo docker run -d --restart=unless-stopped -p 80:80 -p 443:443 rancher/rancher

After the test, it is found that the container is constantly restarted after startup, and there is no way to enter the UI, prompting a network error.

CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS                         PORTS               NAMES
bfd5c52a1ce7        rancher/rancher     "entrypoint.sh"     12 hours ago        Restarting (1) 3 seconds ago                       elated_heisenberg

View log:

[root@k8s-node02 ~]# docker logs --tail 3 bfd5c52a1ce7
ERROR: Rancher must be ran with the --privileged flag when running outside of Kubernetes
ERROR: Rancher must be ran with the --privileged flag when running outside of Kubernetes
ERROR: Rancher must be ran with the --privileged flag when running outside of Kubernetes

If an error is found, it is said that — privileged is required to increase privileges
turn off the lifting appliance — privileged to try:

docker run -d --restart=unless-stopped --privileged  -p 80:80  -p 443:443 rancher/rancher

Found it