I've recently become thoroughly convinced of the merits of consolidating onto as few machines (physical or virtual) as possible. One reason is that I recently consolidated some of my company's infrastructure onto a single bare-metal server to reduce costs. And then in the middle of that, this post came out:

https://rachelbythebay.com/w/2022/01/27/scale/

It seems to me that running lots of small VMs with unikernels is inherently wasteful compared to running many processes on a single machine with a shared kernel that can make optimal use of the machine's resources. Sure, the unikernel-based VMs can be smaller than equivalent Linux VMs, but one still has to allocate a fixed amount of RAM, storage, and (for public cloud platforms) CPU to each VM. We inevitably add some padding to those allocations to ensure that we have headroom, and the total probably adds up to more than we would need to allocate to a single machine (physical or virtual) running all of those processes on a single kernel. And on public cloud platforms, we have to pay for those padded resource allocations.

I've certainly done deployments with lots of small Linux VMs in the past; in my recent migration process, I was replacing such a setup with one big box. Creating lots of small VMs is certainly a convenient and robust way to independently deploy and update several components. But it's obviously not the only way.

The home page of the forthcoming Unikraft Cloud service says, "The cloud is essential to your business but you know you are overpaying." But I think a better answer is to consolidate onto a few big VMs, using container orchestration to keep deployment manageable.