I'd also recommend reading the ECS quickstart in the Bottlerocket repo: https://github.com/bottlerocket-os/bottlerocket/blob/develop...
We do have firecracker-containerd (https://github.com/firecracker-microvm/firecracker-container...) which is designed to allow the containerd runtime to launch containers as microVMs via Firecracker, with that additional layer of isolation via the KVM hypervisor. This stack is not currently fully compatible with K8s or ECS though, so it is not implemented using that approach yet. Rather Bottlerocket is built as a progressive improvement on the current state of container hosts, which is that many people are running all their containers on their hosts without any strong security hardening at all.
I think from the similar naming scheme of Firecracker and Bottlerocket you can already see the pieces of the puzzle that are in progress and the future potential though.
So if I have a heterogeneous collection of servers - I could install Debian, and run docker on Debian. It sounds like bottlerocket would more comfortably run on top of a hypervisor abstracting away the actual hw a bit? Eg on top of xen, kvm or VMware?
Obviously the Linux kernel can be made to run on a toaster, but maybe bottlerocket isn't ideal for that purpose?
Bottlerocket has a GNU userland like many other distros. It is just one that is stripped down of many things including removal of interpreters, shells, and package managers.
If you want to explore more deeply, you can enable the admin container and jump into a shell on the host[1] to look at the filesystem and see what Bottlerocket's userspace looks like up close and personal. You can also see a bit more of this debugging/exploration tooling explained in an AWS Partner Blog[2].
[1] https://github.com/bottlerocket-os/bottlerocket#admin-contai... [2] https://aws.amazon.com/blogs/apn/getting-started-with-bottle...
Sounds exactly like Qubes OS [0], but the latter is probably much more secure (based on Xen and VT-d). So in comparison Bottlerocket seems like trading some of security for performance.
Qubes uses VM's. Subgraph OS is another option. It tries to achieve the same thing with containers, but their latest release is pretty old--not sure how alive that project is.
What are the differences especially regarding their spirit and philosophy?
First Bottlerocket is not Amazon Linux 2, it is its own minimal operating system, with most components built from the ground up in Rust. This is totally different than the Amazon Linux 2 you may be familiar with (and most other operating systems for that matter). Bottlerocket is optimized for running containers with high security isolation. The host OS is extremely minimal, it does not come with bash, an interpreter, ssh, or anything beyond the system basics needed to run containers. In fact it uses an immutable root filesystem. You aren't intended to run or install things directly on the host at all.
Everything that is installed and runs on Bottlerocket runs as containers, which are kept isolated from each other and the host with best practice security features such as SELinux. For example you can connect to a container on the host via AWS Systems Manager, or you can optionally enable a container that lets you connect to it via SSH. Once again the thing you are connecting to is the container on the host though, not directly to the host.
For this initial release of Bottlerocket we are focusing on providing image variants that are prepackaged with the requirements to serve as underlying container hosts for an ECS or EKS cluster. However we also intend Bottlerocket to eventually be something that anyone can use, anywhere, even outside of AWS, if they wanted to benefit from the secure by default, container first design of Bottlerocket.
You can read more about the security features of Bottlerocket here: https://github.com/bottlerocket-os/bottlerocket/blob/develop...
And you can find a bit more of the charter / goals for the project here: https://github.com/bottlerocket-os/bottlerocket/blob/develop...