Step 1: Clear the screen to get an uncluttered view.

clear

Step 2: Confirm that kubectl and minikube are up and running

What a minute or two. It takes a bit of time for minikube to get up and running in the interactive learning environment.

kubectl version

You should see something like this:

Client Version: version.Info{Major:"1", Minor:"13", GitVersion:"v1.13.3", GitCommit:"721bfa751924da8d1680787490c54b9179b1fed0", GitTreeState:"clean", BuildDate:"2019-02-01T20:08:12Z", GoVersion:"go1.11.5", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"13", GitVersion:"v1.13.3", GitCommit:"721bfa751924da8d1680787490c54b9179b1fed0", GitTreeState:"clean", BuildDate:"2019-02-01T20:00:57Z", GoVersion:"go1.11.5", Compiler:"gc", Platform:"linux/amd64"}

Get some general information about the current cluster

kubectl cluster-info

Example Output

Kubernetes master is running at https://172.17.0.74:8443
KubeDNS is running at https://172.17.0.74:8443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy

Clusters and Contexts in Kubernetes

A context binds together a user and a cluster. For example, on this machine there is a cluster named minikube and a user named minikube. The context, minikube bind both together.

To view the configuration file that describes the clusters and context to which this machine can access by executing the following kubectl command:

kubectl config view

Example Output

apiVersion: v1
clusters:
- cluster:
    certificate-authority: /root/.minikube/ca.crt
    server: https://172.17.0.74:8443
  name: minikube
contexts:
- context:
    cluster: minikube
    user: minikube
  name: minikube
current-context: minikube
kind: Config
preferences: {}
users:
- name: minikube
  user:
    client-certificate: /root/.minikube/client.crt
    client-key: /root/.minikube/client.key

To view the current context execute the following kubectl command:

kubectl config current-context

If you want to switch to another context, use the the following command, where CONTEXT_NAME is the name of the context

kubectl config use-context CONTEXT_NAME

cd /root/k8s-4-it-pros/day-1/lesson-03-resources-n-manifests

kubectl api-resources

According to Kubernetes:

"A pod (as in a pod of whales or pea pod) is a group of one or more containers (such as Docker containers), with shared storage/network, and a specification for how to run the containers. A pod’s contents are always co-located and co-scheduled, and run in a shared context. A pod models an application-specific “logical host” - it contains one or more application containers which are relatively tightly coupled — in a pre-container world, being executed on the same physical or virtual machine would mean being executed on the same logical host."

There are two ways to create API Resource objects in Kubernetes, imperatively and declaratively. Let's look at each technique

Create a pod with one container imperatively

Imperative creation is done by issuing a command at the command line. For example the following command will create a pod with the name, pinger with a single container. Type or click:

kubectl run --generator=run-pod/v1 pinger --image=reselbob/pinger:v2.1

Let's see if the pod is running by executing the following command. Type or click:

kubectl get pods

Example Output

NAME     READY   STATUS    RESTARTS   AGE
pinger   1/1     Running   0          12s

To delete the pod, type or click:

kubectl delete pod pinger

Create a pod with one container declaratively

Declarative creation is done using a manfiest file. A manifest file describes the resource to create. A manifest file can be in YAML or JSON format. You create a resource declaratively using the command kubectl apply -f MANIFEST_FILE, WHERE MANIFEST_FILE is the path the manifest file. The following command will create a pod based on the settings it the manifest file, simplepod.yaml. Type or click:

kubectl apply -f ./simplepod.yaml

To view the manifest, type or click:

cat ./simplepod.yaml

Pod creation goes through a number of stages. First, Kubernetes needs to find a node where the pod and the containers in the pod can be stored. Then, container manager takes over and gets the container images defined in the manifest file from the container registry. (DockerHub is the default) Finally, the container will spin up to achieve a status of running.

To determine if the containers in a pod are running, type or click:

kubectl get pods

However, be advised sometimes a container will not be able to spin up for one of a variety of reasons. Then you will need to troubleshoot. The first thing to do is to find out information about the pod and get a sense of how events unfolded. To this, you'll use the kubectl describe command. In this case, because we know the name of the pod is, simplepod, type or click:

kubectl describe pod simplepod

To access the shell of the only container in the pod you just created, simplepod, type or click:

kubectl exec -it simplepod -- sh

Run a command in the shell

printenv

To exit the container's shell and go back to the machine prompt, type or click:

exit

Create a pod with two containers declaratively

kubectl apply -f ./complexpod.yaml

To view the manifest, type or click:

cat ./complexpod.yaml

To access the pinger container, which is one of the two containers in the pod, type or click:

kubectl exec -it complexpod --container pinger -- sh

Run a command in the shell

wget -q -O- localhost:3000

To exit the container's shell and go back to the machine prompt, type or click:

exit