CRDs

CRDs, or Custom Resource Definitions, are Kubernetes extensions that allow users to create new types of resources in their clusters. They serve as a way to introduce custom objects that can be managed through the Kubernetes API server. Once a CRD is defined, users can create instances of custom resources that represent specific applications or services.

A CRD consists of a name, group, version, and scope. The name identifies the resource type, while the group and version determine the API endpoint. The scope specifies whether the resource is namespaced or cluster-wide. Custom resources created from CRDs can be managed by controllers that watch for changes and take appropriate action.

CRDs enable operators and specialized controllers to automate complex applications without modifying the core Kubernetes codebase. They provide a flexible way to extend Kubernetes functionality, allowing teams to model domain-specific objects and their operational requirements. This extensibility has made CRDs fundamental to the Kubernetes ecosystem, supporting various stateful applications and cloud-native services.