DevOps: What is Kubernetes Custom Resource Definition (CRD)?

1apiVersion: apiextensions.k8s.io/v1
2kind: CustomResourceDefinition
3metadata:
4  name: certificaterequests.security.example.com
5spec:
6  group: security.example.com
7  versions:
8  - name: v1
9    served: true
10    storage: true
11    schema:
12      openAPIV3Schema:
13        type: object
14        properties:
15          spec:
16            type: object
17            properties:
18              domain:
19                type: string
20              duration:
21                type: string
22                default: "90d"
23            required: ["domain"]
24          status:
25            type: object
26            properties:
27              ready:
28                type: boolean
29              expiry:
30                type: string
31    subresources:
32      status: {}
33  scope: Namespaced
34  names:
35    plural: certificaterequests
36    singular: certificaterequest
37    kind: CertificateRequest
38    shortNames: ["cr"]
39---
40apiVersion: security.example.com/v1
41kind: CertificateRequest
42metadata:
43  name: my-cert
44spec:
45  domain: example.com
46  duration: "365d"