WIP (7/8/2020)

This page will go through the requirements for a Kubernetes installer based on RA-2.

It differs from the existing comparison of installers, as Kubeadm has been removed. Some of the remaining installers still utilize Kubeadm as a bootstrapping tool, but it will not be considered as an installer by itself.

Component Level Architecture Requirements

The chosen runtime must be conformant with the Kubernetes Container Runtime Interface (CRI) and the Open Container Initiative (OCI) runtime spec.

A list of some of the avaialble OCI runtimes and CRIs can be seen below.

OCI Runtimes:

• RunC (Native)
• Crun (Native)
• Kata-containers (Virtualized)
• gVisor (Sandboxed)
• Nable-containers (Sandboxed)

CRIs:

• Containerd (uses runC by default)
• Cri-o (uses runC by default)

Docker should be mentioned here as well, as it uses containerd and runC as part of the "container engine".

The above comparison table is not complete, but covers a minimum that fulfills the requirement for conformance with Kubernetes CRI and OCI runtime spec. Any installer using Kubeadm has the potential to select between Docker, cri-o and containerd as the container runtime, but this may not be fully supported through the installer. 

Align with the Kubernetes version support policy

The version support policy states that the most recent 3 minor releases (n-2) are supported. The reference implementation, and therefore the Kubernetes installer, must align with this policy.

The specific version of Kubernetes (or more specifically, the tools that are installed) depends to the version of the installer used. Here it is assumed that the most recent installer release is used.

A set of Kubelet features must be enabled

The features are:

• CPU Manager (Beta)
• Device Plugin (Beta)
• Topology Manager (Beta)

As of Kubernetes v1.18, all features are in "Beta" state and enabled by default. Prior to this, Topology Manager has been in "Alpha" state, and had to be enabled through a Kubelet feature-gates.

For Topology Manager to be useful, a policy must be specified using the below argument passed to Kubelet, as the default value of "none" is similar to not having the Topology Manager enabled.

    --topology-manager-policy=[none (default) | best-effort | restricted | single-numa-node]

If the installer uses Kubespray, this can be configured through the `kubelet_custom_flags` variable.