A single VM is indeed the most pragmatic setup that most apps really need. However I still prefer to have at least two for little redundancy and peace of mind. It’s just less stressful to do any upgrades or changes knowing there is another replica in case of a failure.

And I’m building and happily using Uncloud (https://github.com/psviderski/uncloud) for this (inspired by Kamal). It makes multi-machine setups as simple as a single VM. Creates a zero-config WireGuard overlay network and uses the standard Docker Compose spec to deploy to multiple VMs. There is no orchestrator or control plane complexity. Start with one VM, then add another when needed, can even mix cloud VMs and on-prem.