What is a ReplicationController in Kubernetes?

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Question
What is a ReplicationController in Kubernetes?

Answer
It is a component that ensures the pods are constantly running (page 90 and 91 of Kubernetes in Action by Luksa). They were designed to create and manage redundant pods (page 91 of Kubernetes in Action by Luksa). They do just that — they do not transfer pods but create new ones on different nodes (page 93 of Kubernetes in Action by Luksa).

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How Do You Create Your Own kubeconfig File?

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Problem scenario
You want to create a kubeconfig file automatically. But you do not know how. What should you do?

Prerequisites
If kubelet, kubeadm and kubectl are installed, skip the prerequisites to go to step #1 in the procedures. Otherwise, run these commands:

cd /tmp

curl -Lo kubectl https://storage.googleapis.com/kubernetes-release/release/$(curl -s https://storage.googleapis.com/kubernetes-release/release/stable.txt)/bin/linux/amd64/kubectl && chmod +x kubectl

curl -Lo kubeadm https://storage.googleapis.com/kubernetes-release/release/$(curl -s https://storage.googleapis.com/kubernetes-release/release/stable.txt)/bin/linux/amd64/kubeadm && …

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How Do You Troubleshoot the Error “kubelet service is not enabled” or How Do You Write Your Own .service File in Linux?

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Problem scenario
You try to run a kubeadm command. You get an error about kubelet

” [WARNING Service-Kubelet]: kubelet service is not enabled, please run ‘systemctl enable kubelet.service'”

How do you get “sudo systemctl start kubelet” or “sudo systemctl enable kubelet” to work? How do you create your own kubelet.service file?

Solution

  1. Create this file: /etc/systemd/system/kubelet.service
  2. The content should be as follows (but you may need to double check that the kubelet file is there;

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How Do You Troubleshoot the Google Kubernetes Engine error “Request had insufficient authentication scopes”?

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Problem scenario
 You run a command like this:
gcloud container clusters get-credentials standard-cluster-1 –region us-central1-a

But you receive one of the following messages:
“Fetching cluster endpoint and auth data.
ERROR: (gcloud.container.clusters.get-credentials) ResponseError: code=403, message=Request had insufficient authentication scopes.”

ERROR: (gcloud.projects.describe) User [123456789-compute@developer.gserviceaccount.com] does not have permission to access projects instance [123456789] (or it may not exist): Request had insufficient
authentication scopes.

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How Do You Troubleshoot This Error “error executing access token command /google/google-cloud-sdk/bin/gcloud”?

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Problem scenario
You run a command like this to view your Google Kubernetes Engine (GKE) clusters:

kubectl get pods

You see this:
‘Unable to connect to the server: error executing access token command “/google/google-cloud-sdk/bin/gcloud config config-helper –format=json”: err=fork/exec /google/google-cloud-sdk/bin/gcloud: no such file or directory output= stderr=’

What should you do?

Solution
Check your config file in the .kube directory.

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How Do You Install Helm on Any Type of Linux?

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Problem scenario
You want to use Helm to manage Kubernetes applications. Helm helps you with packages for changes to Kubernetes (in ways that are similar to yum or apt). Helm uses what are called Charts (.yaml files) that enable you to do more with Kubernetes with less trouble. Helm consists of these two things: a CLI tool and a server component that runs as a pod in a Kubernetes cluster (page 531 of Kubernetes in Action by Luksa).

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How Do You Troubleshoot the Kubernetes Problem “connection to the server localhost:8080 was refused”?

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One of the following applies (with #1 being related to Kubernetes anywhere and #2 only being relevant to running Kubernetes in GCP).

Problem scenario #1 (any Kubernetes)
You run a command like this: kubectl get svc

You get an error like this: The connection to the server localhost:8080 was refused – did you specify the right host or port?

What should you do?

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How Do You Troubleshoot a kubectl Command That Returns “The connection to the server localhost:8080 was refused – did you specify the right host or port?” when using AWS and EKS?

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One of the following problems pertains to you.

Problem scenario #1
You have a kubectl server. You created some new EKS clusters. How do you get the kubectl server to interface, control or manage the new EKS clusters.

or

Problem scenario #2
You are running EKS. You run this command:

kubectl get cluster-info

But you receive this message: “The connection to the server localhost:8080 was refused – did you specify the right host or port?”

What should you do?

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What Are The Advantages of a Service over an Ingress in Kubernetes?

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Problem scenario
You have read that Ingresses have benefits compared to Services. You know the two are different for routing external traffic to reach a Kubernetes pod. When would you want to use a Service instead of an Ingress?

Possible Answers

  1. When you want to direct traffic to Pods based on a selector and not an IP address. Ingresses use IP addresses*,

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