I'm also seeing:

2025/09/02 18:31:25 [FATAL] Internal error occurred: failed calling webhook "<http://rancher.cattle.io.settings.management.cattle.io|rancher.cattle.io.settings.management.cattle.io>": failed to call webhook: Post "<https://rancher-webhook.cattle-system.svc:443/v1/webhook/validation/settings.management.cattle.io?timeout=10s>": no endpoints available for service "rancher-webhook"

this sounds like https://github.com/rancher/rancher/issues/51571#issuecomment-3205285125

I will check that issue out, thanks @creamy-pencil-82913 . And yes, I realize docker is not supported for production. This is not production yet, but we plan on migrating to running it on some form of K8s before production. We just haven’t had time to research and perform the migration yet. Out of curiosity, besides docker not supporting HA, what is the reason it’s not supported? Is it because the docker container runtime is not as reliable as containerd?

it runs completely differently in the docker container, and does not see the same amount of testing since it is not a preferred deployment pattern

Ah ok, that makes sense. What is the simplest way to set up a cluster to install Rancher on? Is it an option to create a RKE2 cluster via Rancher and then migrate Rancher over to it or does it have to be created without using Rancher?

You have to create it first. Simplest supported option would be k3s, which you can run in docker.

Ok. And if I go with RKE2 to match our downstream clusters, that can be installed standalone without having to create it via Rancher, correct? And once it's created and Rancher is deployed on it, is that cluster what will show as "local" in the Rancher UI (what is currently our single node docker container running k3s)?

Correct