How do you manage on-prem servers?

Well it really depends on what you need by on-prem-servers

Are you trying to provision services and apps? Kubernetes. Are you trying to provision Virtual machines? have a look at rancher harvester. Are you trying to replicate server setup to make it unified? Ansible Are you trying to explicitly control servers with instructions? Terraform

SSH works in containers too, all you have to do is either open the ports or forward.

Once they finish their ipv6 features, Rancher Harvester is going to be one interesting beast for on-premise. You may setup your virtual machines with the regular kubernetes api (libvirt), provision storage throughout the network and could even dife into software defined everything.

If none of these words mean anything to you though, the most common way for smaller orgs is either ansible or terreaform. Dont complicate things just to make them shiny ;)

On prem or in the cloud servers are very similar. I use Terraform, Ansible, kubernetes, teleport, Prometheus, ArgoCD to name a few.

The most complex thing perhaps is to configure the storage encryption with LUKS or similar. You get that for free in the cloud if you don’t care about letting your cloud provider play with your private keys.

Ubuntu MAAS to provision servers - when new server arrives guys at the DC just need to plug it in and power it once, everything else is just clicking around.

Pyinfra to manage and install software (I'm fed up with custom DSLs, pyinfra is pure python)

Ubuntu MaaS, OpenStack Ansible for control plane, Ansible for hypervisor provisioning. Probably overkill unless you are running hundreds of hosts

Ubiquity auto-install + Cloud-init to build, Ansible for anything cloud-init can't do, Prometheus , promtail, Loki, grafana to monitor.

I've wanted to try Digital Rebar but I haven't gotten an opportunity yet. I never had good experiences with Canonical MaaS.