Basic kubernetes

Setup

This section assumes you've completed the quickstart section.

You need to be aware of which namespace you’re working in, and either set it with kubectl config set-context nautilus --namespace=the_namespace or specify in each kubectl command by adding -n namespace.

Explore the system

To get the list of cluster nodes (although you may not have access to all of them), type:

kubectl get nodes

Right now you probably don't have anything running in the namespace, and these commands will return No resources found in ... namespace.. There are three categories we will examine: pods, deployments and services. Later these commands will be useful to see what's running:

List all the pods in your namespace

kubectl get pods

List all the deployments in your namespace

kubectl get deployments

List all the services in your namespace

kubectl get services

Launch a simple pod

Let’s create a simple generic pod, and login into it.

You can copy-and-paste the lines below. Create the pod1.yaml file with the following contents:

apiVersion: v1
kind: Pod
metadata:
  name: test-pod
spec:
  containers:
  - name: mypod
    image: ubuntu
    resources:
      limits:
        memory: 100Mi
        cpu: 100m
      requests:
        memory: 100Mi
        cpu: 100m
    command: ["sh", "-c", "echo 'Im a new pod' && sleep infinity"]

Reminder, indentation is important in YAML, just like in Python.

If you don't want to create the file and are using mac or linux, you can create yaml's dynamically like this:

kubectl create -f - << EOF
<contents you want to deploy>
EOF

Now let’s start the pod:

kubectl create -f pod1.yaml

See if you can find it:

kubectl get pods

Note: You may see the other pods too.

If it is not yet in Running state, you can check what is going on with

kubectl get events --sort-by=.metadata.creationTimestamp

Events and other useful information about the pod can be seen in describe:

kubectl describe pod test-pod

If the pod is in Running state, we can check it's logs

kubectl logs test-pod

Let’s log into it

kubectl exec -it test-pod -- /bin/bash

You are now inside the (container in the) pod!

Does it feel any different than a regular, dedicated node?

Try to create some directories and some files with content.

(Hello world will do, but feel free to be creative)

We will want to check the status of the networking.

But ifconfig is not available in the image we are using; so let’s install it.

First, let's make sure our installation tools are updated.

apt update

Now, we can use apt to install the necessary network tools.

apt install net-tools

Now check the networking:

ifconfig -a

Get out of the Pod (with either Control-D or exit).

You should see the same IP displayed with kubectl

kubectl get pod -o wide test-pod

We can now destroy the pod

kubectl delete -f pod1.yaml

Check that it is actually gone:

kubectl get pods

Now, let’s create it again:

kubectl create -f pod1.yaml

Does it have the same IP?

kubectl get pod -o wide test-pod

Log back into the pod:

kubectl exec -it test-pod -- /bin/bash

What does the network look like now?

What is the status of the files your created?

Finally, let’s delete explicitly the pod:

kubectl delete pod test-pod

Let’s make it a deployment

You saw that when a pod was terminated, it was gone.

While above we did it by ourselves, the result would have been the same if a node died or was restarted.

In order to gain a higher availability, the use of Deployments is recommended. So, that’s what we will do next.

You can copy-and-paste the lines below.

dep1.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: test-dep
  labels:
    k8s-app: test-dep
spec:
  replicas: 1
  selector:
    matchLabels:
      k8s-app: test-dep
  template:
    metadata: 
      labels:
        k8s-app: test-dep
    spec:
      containers:
      - name: mypod
        image: ubuntu
        resources:
           limits:
             memory: 500Mi
             cpu: 500m
           requests:
             memory: 100Mi
             cpu: 50m
        command: ["sh", "-c", "sleep infinity"]

Now let’s start the deployment:

kubectl create -f dep1.yaml

See if you can find it:

kubectl get deployments

The Deployment is just a conceptual service, though.

See if you can find the associated pod:

kubectl get pods

Once you have found its name, let’s log into it

kubectl get pod -o wide test-dep-<hash>
kubectl exec -it test-dep-<hash> -- /bin/bash

You are now inside the (container in the) pod!

Create directories and files as before.

Try various commands as before.

Let’s now delete the pod!

kubectl delete pod test-dep-<hash>

Is it really gone?

kubectl get pods

What happened to the deployment?

kubectl get deployments

Get into the new pod

kubectl get pod -o wide test-dep-<hash>
kubectl exec -it test-dep-<hash> -- /bin/bash

Was anything preserved?

Let’s now delete the deployment:

kubectl delete -f dep1.yaml

Verify everything is gone:

kubectl get deployments
kubectl get pods