Tip: Failed to create pod sandbox: rpc error: code = Unknown desc = failed to setup network for sandbox

Kubelet report such error when you deploy a pod: 

Failed to create pod sandbox: rpc error: code = Unknown desc = failed to setup network for sandbox : "*****"  error getting ClusterInformation: connection is unauthorized: Unauthorized

It's due to CNI is not set up well or is not functioning on the node. 

Redeploy the CNI provider may help. i.e. Flannel or Calico

Tip: How to get Go Client in Kubernetes Operator Reconcile()

Requirement:

      When we build a K8S operator via kubebuilder, we often need to interact with Control Plane. By default, we use controller-runtime client 

 However, when we use this client to fulfil some functions of kubectl i.e. drain, we hit an error:

 cannot use r.Client (variable of type client.Client) as kubernetes.Interface value in struct literal: missing method AdmissionregistrationV1

Solution:

The error indicates the controller-runtime client does not implement method AdmissionregistrationV1, so we can't use it, instead, we init a new GO Client in the reconcile(). Sample code is like

"k8s.io/client-go/kubernetes"

ctrlconfig "sigs.k8s.io/controller-runtime/pkg/client/config"

cfg, err := ctrlconfig.GetConfig()

if err != nil {

log.Log.Error(err, "unable to get kubeconfig")

return err

}

kubeclientset, err := kubernetes.NewForConfig(cfg)

if err != nil {

return err

}

Tip: Understand why no user concept in Kubernetes Authentication

 One main authentication mechanism in K8S is:   CA, Certificate, Key

There is no "user"  concept in K8S. Instead, it uses the client private key to identify the "user"

The workflow is like this:

• Users(clients) have their private keys. These keys represent their unique id in K8S.
• Go through the CSR approval process with these keys. We can add CN like user "John" into the CSR process to have a readable "user" id.
• Once CSR is approved, we can get a signed certificate of the private key representing the user "John"
• Then we can authenticate in K8S via  CA, Certificate, Key

Pass CKA Exam Tips

On Thursday, I passed the CKA exam with a 93 score mark and get the certificate. I share some tips on how I achieve that.

• 17 questions in 2 hours. 
• Don't worry about copy and paste. You can copy it by clicking it when your mouse hovers on the "important text".
• Read each question carefully. Always understand questions before starting to do it. Check the weight of each question. The high weight means more mark points in the question. 
• Skip the difficult questions and make sure you get easy marks.  Only a 66 score mark is needed to pass the exam. 
• Practise and create examples for each test point in the CKA curriculum
• Strongly recommend this udemy course.  The practice and mock exams are great to prepare for CKA exams.
• Practise all commands in the kubectl cheatsheet