~~Stop. Docker is not a hypervisor and shouldn't be used as one.

Either use a docker compose file to do automated deployments or move to Proxmox and use host templates to deploy VMs which then can host docker.

There is zero reason to run KVM in docker.~~

Never mind, I misread. What you are looking for is Ansible. You can create a VM template that has your SSH keys configured and then you use Ansible to spin up a VM and do stuff instead the VM. I know how to do this under Proxmox but I have no idea how to do it under pure Debian. A lot of it is probably the same.

When I change my server, I always start from scratch, hoping that it will come out better.

I don't know what I'm expecting, it was always working well..

I just use a few shell scripts. Basically some simple bash scripts that do all the work after a fresh install.

Kubernetes/Ansible are great to learn, but are also more complicated for simple setups.

Personally, if you're considering it already, kubernetes might be something to look into. It's a lot. Like a lot to learn. But I can honestly say I could do it for a job now with how much I've learned. Then it's less about how to set up machines and more about just reapplying your infrastructure.

I'm now using Fedora CoreOS which can be deployed from config files. It's really neat to be able to define everything the way you need it and just start up the VM with no further config necessary. I'm using podman to manage my services.