Error parsing hosts.toml without any `host` tree about containerd HOT 3 OPEN

Does it work fine without the extra [host] in there?

No, it does not work at all without the [host] in there. You could also add a [host."example.com"] entry but I don't need to configure any mirrors, I just want to set the ca for this registry namespace.

That shouldn't be a valid configuration

Nowhere in the docs does it indicate that you MUST have a host tree. If you just want to configure TLS for the registry namespace without specifying any mirrors, having root fields set without a host tree (ie no host blocks) is a perfectly valid use case.

from containerd.

The change from #9131 appears to have refactored some of this, but I'm not sure if it actually resolved the issue or not.

It does still affect the 1.7 branch:
https://github.com/containerd/containerd/blob/v1.7.14/remotes/docker/config/hosts.go#L529-L534

from containerd.

root@systemd-node-1:/# cat /var/lib/rancher/k3s/agent/etc/containerd/certs.d/172-17-0-7.sslip.io/hosts.toml
ca = ["/usr/local/share/ca-certificates/registry.crt"]
[host]

Does it work fine without the extra [host] in there? That shouldn't be a valid configuration, although it should be handled more gracefully.

from containerd.