CAPI Runtime Extensions

Cluster API provides declarative APIs for provisioning, upgrading, and operating Kubernetes clusters across multiple infrastructure providers. The ClusterClass feature brings huge improvements in how users manage clusters, providing a single resource for a user to mutate to orchestrate upgrades, etc. ClusterClass also brings much improved templating over the clusterctl generate cluster environment-variable driven templating by introducing variables specified with an OpenAPI schema that can then be applied to the generated resources via patches.

The Runtime SDK feature provides an extensibility mechanism to hook into ClusterClass managed Kubernetes clusters' lifecycle. This project, CAPI Runtime Extensions, provides implementations of various runtime hooks that can be used in ClusterClasses across providers. This includes variables and patches that can be used across any provider to configure generic Kubernetes capabilities, such as configuring audit policy or HTTP proxy configuration. These capabilities are not provider-specific and delivering these capabilities in code instead of directly embedded in ClusterClass definitions leads to a much more robust experience via fast-feedback unit tests, as opposed to long running e2e tests.

In addition to cluster resource customizations, this project enables management of essential cluster addons (e.g. CNI) via variable definitions, e.g. selecting a CNI provider via variables defined on the Cluster resource itself. The goal is to provide a single resource, the Cluster, that a user has to interact with to describe a fully-operational Kubernetes cluster.