KodeCloud CKAD Custom Resource Definition

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Custom Resource Definition (CRD)

• For every resource we have controller.
  • So when we create a resource it is stored in etcd.
  • Controller continuously watches the status of these objects to maintain the state as expected.
• Custom resource and custom controller
  • Flight ticket booking resource
  • We will need to create a flight ticket booking controller.
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• We need a CRD to tell k8s about the resource that we want to create.
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Once we create a CRD we can create the custom resource.

• We use CRD to create any kind of resource in k8s.
• Creating a CRD only allows us to create custom resources and store them on etcd.
  • Since we don't have a controller yet.
  • A custom resource without a controller is just data sitting in etcd and does not do anything.

So there are 2 steps for creating any custom resource in k8s

• Defining a CRD
• Writing a controller

• We write a custom controller using the go programming language.
  • Once we build the controller we compile it.
  • We specify the kubeconfig file that the controller can use to authenticate to the k8s api.
  • We may choose to package the custom controller as a docker image and run it as a pod or deployment.

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Last updated: 2022-10-10