# Kube 101

## Requirements

- Docker Engine 19.03+ (tested successfully with Docker4Mac or Docker Linux)
- `k3d` binary installed on your PATH (<https://github.com/rancher/k3d>)
- `kubectl` binary installed on your PATH (<https://kubernetes.io/docs/tasks/tools/install-kubectl/>)
- A bash prompt

## Create Kubernetes Cluster

- Using the `k3d` command, create a Kubernetes cluster with the following properties:
  - 1 master node and 3 worker nodes,
  - ports 80 and 443 published on the `localhost` interface of your host machine,

```bash
k3d create --publish="80:80" --publish="443:443" --workers="3"
```

- 4 docker containers are now running: 1 for the master node and 3 for the worker nodes:

```bash
docker ps
```

## Configure `kubectl`

- Use the configuration generated by `k3d` for `kubectl`,
by following the instructions from `k3d` output:

```bash
export KUBECONFIG="$(k3d get-kubeconfig --name='k3s-default')"
kubectl cluster-info
```

You should see the following output:

```text

Kubernetes master is running at https://localhost:6443
CoreDNS is running at https://localhost:6443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy

To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
```

## Interact with Kubernetes API

- Check the cluster topology:

```bash
kubectl get nodes
# You should see 1 master and 3 workers
```

- Check the pods running, cluster wide:

```bash
$ kubectl get pod --all-namespaces

NAMESPACE     NAME                         READY   STATUS      RESTARTS   AGE
kube-system   coredns-b7464766c-mtj2k      1/1     Running     0          3m45s
kube-system   helm-install-traefik-bw2tg   0/1     Completed   0          3m46s
kube-system   svclb-traefik-9fknp          2/2     Running     0          3m27s
kube-system   svclb-traefik-ppffn          2/2     Running     0          3m27s
kube-system   svclb-traefik-vxdlk          2/2     Running     0          3m27s
kube-system   svclb-traefik-z7wfh          2/2     Running     0          3m27s
kube-system   traefik-56688c4464-r8ctk     1/1     Running     0          3m27s
```

- Open the URL <http://localhost>: you should see a `404 page not found` page. It means an HTTP server is answering in the cluster on port 80.

## Deploy the Example Web Application

- Create the namespace named `whoami`:

```bash
$ kubectl get namespaces
NAME              STATUS   AGE
default           Active   5m56s
kube-node-lease   Active   5m56s
kube-public       Active   5m56s
kube-system       Active   5m56s
# No "whoami" namespace

$ kubectl apply -f ./whoami-namespace.yml
namespace/whoami created

$ kubectl get namespaces
NAME              STATUS   AGE
default           Active   6m46s
kube-node-lease   Active   6m46s
kube-public       Active   6m46s
kube-system       Active   6m46s
whoami            Active   14s
# New "whoami" namespace
```

- Create the "deployment", which should create 2 pods (because 2 replicas).
  The "whoami" container is a web application listening on its port `80`
  which respond to HTTP `GET` requests by responding (body) the headers of the request:

```bash
$ kubectl get pod --namespace=whoami
No resources found in whoami namespace.

$ kubectl apply -f ./whoami-deployment.yml
deployment.extensions/whoami created

kubectl get pod --namespace=whoami
NAME                      READY   STATUS    RESTARTS   AGE
whoami-756586b9ff-h4vlq   1/1     Running   0          8s
whoami-756586b9ff-j6sqg   1/1     Running   0          8s
```

- Expose + Load Balance the 2 replicated pod of the deployment by creating a new "service":

```bash
$ kubectl get service --namespace=whoami
No resources found in whoami namespace.

$ kubectl apply -f ./whoami-service.yml
service/whoami created

$ kubectl get service --namespace=whoami
NAME     TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)   AGE
whoami   ClusterIP   <IP>            <none>        80/TCP    13s
```

- Spawn a new pod in the same namespace, with an interactive shell
  to request the "service" and see loadbalancing happening (look at `IP:` field on the response body):

```bash
kubectl run --tty -i --rm --image=alpine --namespace=whoami -- sh
(...)
/ # apk add --no-cache curl # Install curl
(...)
/ # curl http://<IP>:80 # Wher <IP> is the "cluster IP" of the service
(...)
/ # curl http://<IP>:80 # Wher <IP> is the "cluster IP" of the service
(...)
/ # exit
(...)
deployment.apps "sh" deleted
```

- Publish the "service" to outside the cluster by creating a new "Ingress",
  that will be implemented by Traefik, the Ingress Controller of the cluster:

```bash
$ kubectl get ingress --namespace=whoami
No resources found in whoami namespace.

$ kubectl apply -f whoami-ingress.yml
ingress.extensions/whoami created

$ kubectl get ingress --namespace=whoami
NAME     HOSTS       ADDRESS      PORTS   AGE
whoami   localhost   172.30.0.2   80      7s
```

- You can now open the URL <http://localhost:80> and access the web service.
  If you reload the page, you'll see the same "load balancing" behavior as earlier with `curl`.

## Cleanup

Destroy the cluster with `k3d delete` (check with `docker ps`).

## Going Further

- <https://medium.com/@geraldcroes/kubernetes-traefik-101-when-simplicity-matters-957eeede2cf8>
- <https://kubernetes.io/docs/tutorials/kubernetes-basics/>