K8s in 30 mins

This is not a comprehensive guide to learn Kubernetes from scratch, rather this is just a small guide/cheat sheet to quickly setup and run applications with Kubernetes and deploy a very simple application on single workload VM. This repo can be served as quick learning manual to understand Kubernetes.

Prerequisite

Setting up Kubernetes cluster in VM (NOT MINIKUBE) : 1 VM cluster
- Spining up a virtual machine with Vagrant : 2GB RAM + 2CPU cores (at least)
- Understanding:
  - kubeadm
  - kubelet
  - kubectl
Kuberenetes pods: How are they different than Docker containers.
- Moving from Docker container to Kubernetes pods.
Kubernetes Resource:
Kubernetes network manager
- I will pick up the plugin called Flannel.
Stateless Workload
- Replicasets & Deployments
Stateful Workloads
- Persistent Volumes
- Persistent Volume Claims
Deploying End-to-End Service in Kubernetes cluster
- MySQL:
  - PV
  - PVC
  - Deployment
  - Service
- Sprinboot Application:
  - Stateless Workload
    - Custom Docker Image
  - Replica based Deployment & link with DB Service
  - Access Springboot Service outside Pods
- Infrastructure as a Code
  - MySQL Full Spec
  - AppServer Full Spec
Understanding advance kubernetes resources:
- Namespaces
  - Create Namespace and Add Resource
- Context
Cheat sheet
Next steps

Setting up Kubernetes cluster in VM

Download the Vagrant File.
Download Virtual box and install from here.
Download and install Vagrant.
In the terminal, run the two command to get the VM up and running, with out any configuration 😄
```
# In the same directory where you have downloaded Vagrantfile, run
vagrant up
vagrant ssh
```
This will download the Ubuntu box image and do the entire setup for you with the help of virtual box. It just need virtual box installed.
The Vagrantfile comes preconfigured with kubeadm, kubelet, kubectl

Check if kubernetes cluster is perfectly installed.

root@vagrant:/home/vagrant# kubectl version -o json
{
  "clientVersion": {
    "major": "1",
    "minor": "19",
    "gitVersion": "v1.19.2",
    "gitCommit": "f5743093fd1c663cb0cbc89748f730662345d44d",
    "gitTreeState": "clean",
    "buildDate": "2020-09-16T13:41:02Z",
    "goVersion": "go1.15",
    "compiler": "gc",
    "platform": "linux/amd64"
  },
  "serverVersion": {
    "major": "1",
    "minor": "19",
    "gitVersion": "v1.19.2",
    "gitCommit": "f5743093fd1c663cb0cbc89748f730662345d44d",
    "gitTreeState": "clean",
    "buildDate": "2020-09-16T13:32:58Z",
    "goVersion": "go1.15",
    "compiler": "gc",
    "platform": "linux/amd64"
  }
}

Start the Kubernetes cluster master node.

# This will spin up Kubernetes cluster with CIDR: 10.244.0.0/16
root@vagrant:/home/vagrant# kubeadm init --pod-network-cidr=10.244.0.0/16
kubeadm join 10.0.2.15:6443 --token 3m5dsc.toup1iv7670ya7wc --discovery-token-ca-cert-hash sha256:73f4983d43f9618522eaccf014205f969e3bacd76c98dd0c

root@vagrant:/home/vagrant# mkdir -p $HOME/.kube
root@vagrant:/home/vagrant# sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
root@vagrant:/home/vagrant# sudo chown $(id -u):$(id -g) $HOME/.kube/config

Conenct other VM to this cluster: Not required in case of single VM cluster. For this run perfectly, make sure:
- VM to VM connectivity is there.
- All there kube-* are installed in VM.
```
kubeadm join 10.0.2.15:6443 --token 3m5dsc.toup1iv7670ya7wc --discovery-token-ca-cert-hash sha256:73f4983d43f9618522eaccf014205f969e3bacd76c98dd0c
```
At this point, Kubernetes is installed and cluster master is up, but still we need a agent to provision and manager network for new nodes for us, This is where Flannel comes to rescue. Install Flannel to manager docker network for pods.
```
kubectl apply -f \
    https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml
```

This step applies, if we wish to use, our master node as worker as well. Which is yes in our case:

root@vagrant:/home/vagrant# kubectl taint nodes $(hostname) node-role.kubernetes.io/master:NoSchedule-

# If everything goes well, you will see something like this.
root@vagrant:/home/vagrant# kubectl get node
NAME      STATUS   ROLES    AGE     VERSION
vagrant   Ready    master   3m40s   v1.19.2

Run all the commands from root shell.

What are kube*

Kubernetes runs in client server model, similar to the way the docker runs. Kubernetes server exposes kubernetes-api, and each of kubeadm, kubelet and kubectl connect with this kubernetes server api to get the task done. In the master slave model, there are two entities:

Control Plane
Worker Nodes

Control Plane : Connects with Worker nodes for resource allocation.
Worker nodes : Cluster entitiy that actually allocates tasks and run Pods.

kubeadm:
- Sets-up the cluster
- Connect various worker nodes togather.
kubectl:
- It is a client cli.
- Connects with control plane kubernetes api server and send execution requests to control plane.
kubelet:
- Receives request from control planes.
- Runs in Worker nodes.
- Runs task over worker nodes.
- Maintain Pod lifecycle. Not just for pods, but all Kubernetes resources lifecycle.

Kubernetes pods

Pods run multiple containers.
Pods abstract out multilpe containers into single unit.
If two service in pods are both exposing service on same port, the other one wont spin up and it will fail.
The unit of Kubernetes work load is called Pod.

How to create a pod

You can create a simple nginx pod with following yaml spec. Save this in file name : pod.yml

apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
  - name: nginx
    image: nginx

Key name	Key Description
`apiVersion`	Kubernetes server API
`kind`	Kubernetes Resource type: `Pod`
`metadata.name`	Name of Kubernetes Pod
`spec.container.name`	Name of Container which will run in a Pod
`spec.container.name`	Name of docker image to run

Run this Pod spec with. kubectl apply -f pod.yml

root@vagrant:/home/vagrant/kubedata# kubectl apply -f pod.yaml
pod/nginx created

# If everything goes OK, you will se something like this.

root@vagrant:/home/vagrant/kubedata# kubectl get pods
NAME    READY   STATUS    RESTARTS   AGE
nginx   1/1     Running   0          43s
root@vagrant:/home/vagrant/kubedata#

Use : kubectl get pods to get the list of all Pods.

Running command into container, running inside Pod. kubectl exec -it <pod_name> -c <container_name> -- <command>

root@vagrant:/home/vagrant/kubedata# kubectl exec -it nginx -c nginx -- whoami
root

root@vagrant:/home/vagrant/kubedata# kubectl exec -it nginx -c nginx -- /bin/sh
# cat /etc/*-release
PRETTY_NAME="Debian GNU/Linux 10 (buster)"
NAME="Debian GNU/Linux"
VERSION_ID="10"
VERSION="10 (buster)"
VERSION_CODENAME=buster
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"

Running multiple container in one pod.

apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
  - name: nginx
    image: nginx
  - name: curl
    image: appropriate/curl
    stdin: true
    tty: true
    command: ["/bin/sh"]

Save this into pod-with-two-containers.yml.
Run this : kubectl apply -f pod-with-two-containers.yml

Delete a running pod. kubectl delete -f pod-with-two-containers.yml. This will remove the pod mentioned in spec file.

Container in a Pod can connect to another container in same pod with spec.containers.name.

root@vagrant:/home/vagrant/kubedata# kubectl exec -it nginx -c curl -- /bin/sh
# curl nginx
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
    body {
        width: 35em;
        margin: 0 auto;
        font-family: Tahoma, Verdana, Arial, sans-serif;
    }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>
#

Kubernetes Resources

Pods

Fundamental unit of k8s cluster.
Abstraction for container/multiple-containers, running under single name.
Discussed in detail : here

Deployments

A Deployment provides declarative updates for Pods.
The configuration state in yml file, defines how the pods will run in cluster. They can specify:
- Replicas
- Resource allocation
- Connection with Volumes etc.
- We will see example once we see replicasets

Replicasets

Run deployments in replicas.

Create file with following specification.

apiVersion: apps/v1

kind: Deployment
metadata:
  name: nginx

spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx-app
  template:
    metadata:
      labels:
        app: nginx-app
    spec:
      containers:
      - name: nginx
        image: nginx

Notice the difference.

-- kind: Pod
++ kind: Deployment

++ spec:
++  replicas: 3
++  selector:
++    matchLabels:
++      app: nginx-app

Remove existing pods(if any) kubectl delete pods --all, and create deployment.

root@vagrant:/home/vagrant/kubedata# kubectl apply -f deployment-replica.yml
deployment.apps/nginx created

root@vagrant:/home/vagrant/kubedata# kubectl get deployments
NAME    READY   UP-TO-DATE   AVAILABLE   AGE
nginx   0/3     3            0           7s

root@vagrant:/home/vagrant/kubedata# kubectl get deployments -w
NAME    READY   UP-TO-DATE   AVAILABLE   AGE
nginx   1/3     3            1           14s
nginx   2/3     3            2           20s

Get the list of all deployments: kubectl get deployments or kubectl get deploy

Get the list of all replicaset : kubectl get replicaset or kubectl get rs

root@vagrant:/home/vagrant/kubedata# kubectl get pods
NAME                    READY   STATUS    RESTARTS   AGE
nginx-d6ff45774-f84l8   1/1     Running   0          4m59s
nginx-d6ff45774-gzxfz   1/1     Running   0          4m59s
nginx-d6ff45774-t69mw   1/1     Running   0          4m59s

root@vagrant:/home/vagrant/kubedata# kubectl get deploy
NAME    READY   UP-TO-DATE   AVAILABLE   AGE
nginx   3/3     3            3           162m

root@vagrant:/home/vagrant/kubedata# kubectl get replicaset
NAME              DESIRED   CURRENT   READY   AGE
nginx-d6ff45774   3         3         3       162m

root@vagrant:/home/vagrant/kubedata#

Print a detailed description of the selected resources, including related resources such as events or controllers: kubectl describe <resource_type> <resouce_name>
Get deployment configuration in JSON format: kubectl get deployment nginx -o yaml.

Services

Logical abstraction of Pods and policies to access them.
They enable loose coupling between dependent Pods. e.g
- Open Ports.
- Security Policies between Pod interaction etc.
Can be created independent of Pod declaration, but usually services linked to one Pod are present in same spec file.
Lets create a simple service to expose nginx service port to host machine. File

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx-app
  template:
    metadata:
      labels:
        app: nginx-app
    spec:
      containers:
      - name: nginx
        image: nginx
---
apiVersion: v1
kind: Service
metadata:
  name: nginx
spec:
  selector:
    app: nginx-app
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80

Service declaration starts by augmenting exiting deployment/pod spec with ---.
Service and Pod can share same names.
- Each different resource must have unique amongst themselves.
The above service, exposes port 80 on host specified by spec.ports.port to port 80 of target pod specified by spec.ports.taregtPort

root@vagrant:/home/vagrant/kubedata# kubectl apply -f nginx-service.yml
deployment.apps/nginx unchanged
service/nginx created

root@vagrant:/home/vagrant/kubedata#

Once the service is created:

Run : kubectl get services to get the list of services.

root@vagrant:/home/vagrant/kubedata# kubectl get services
NAME         TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)   AGE
kubernetes   ClusterIP   10.96.0.1        <none>        443/TCP   2d5h
nginx        ClusterIP   10.104.178.240   <none>        80/TCP    49s

Cluster IP is the IP interface of Pod anstraction on host. curl cluster IP will connect us to the Pod.

root@vagrant:/home/vagrant/kubedata# curl 10.104.178.240
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
    body {
        width: 35em;
        margin: 0 auto;
        font-family: Tahoma, Verdana, Arial, sans-serif;
    }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

Run : kubectl get endpoints or kubectl get ep to get list of exposed endpoints.

root@vagrant:/home/vagrant/kubedata# kubectl get ep
NAME         ENDPOINTS                                    AGE
kubernetes   10.0.2.15:6443                               2d5h
nginx        10.244.0.10:80,10.244.0.8:80,10.244.0.9:80   2m

Since I am running 3 different replicas, we are seeing 3 different Pod IPs.

Loadbalancer Service

Notice External IP in:

root@vagrant:/home/vagrant/kubedata# kubectl get services
NAME         TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)   AGE
kubernetes   ClusterIP   10.96.0.1        <none>        443/TCP   2d5h
nginx        ClusterIP   10.104.178.240   <none>        80/TCP    49s

Since we are running this in local setup, we dont have any CCM(Cloud Config manager), which can provision external IP for us to connect to the service running inside the Pod.
- In case of Azure or AWS Cloud providers, the CCM provisions and links external IPs for us.

So lets do a hack here.

Update nginx service to LoadBalancer. File

apiVersion: v1
kind: Service
metadata:
  name: nginx
spec:
  type: LoadBalancer
  selector:
    app: nginx-app
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80

Notice:

spec:
++ type: LoadBalancer

Apply the config: kubectl apply -f nginx-service-lb.yml

root@vagrant:/home/vagrant/kubedata# kubectl get svc
NAME         TYPE           CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
kubernetes   ClusterIP      10.96.0.1        <none>        443/TCP        2d5h
nginx        LoadBalancer   10.104.178.240   <pending>     80:32643/TCP   17m

Now the state is pending :)

Run netstat -nltp, and notice the kube-proxy

++ tcp        0      0 0.0.0.0:32643           0.0.0.0:*               LISTEN      13095/kube-proxy
   tcp        0      0 127.0.0.1:10248         0.0.0.0:*               LISTEN      7024/kubelet
++ tcp        0      0 127.0.0.1:10249         0.0.0.0:*               LISTEN      13095/kube-proxy

See the magic.

root@vagrant:/home/vagrant/kubedata# curl 0.0.0.0:32643
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
    body {
        width: 35em;
        margin: 0 auto;
        font-family: Tahoma, Verdana, Arial, sans-serif;
    }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

The LoadBalancer exposed the service endpoints out of Kubernetes cluster IP interface and in our vagrant host we can access it now directly :)
The next challenge to to expose this kube-proxy interface to host machine. And hack is done, then we can access the service running in Pod(replica set deployment) from our host interface directly.

This is how the network now looks like. The port 32643 is not exposed through kube-proxy over host/control-plane node.

                                                  Kubernetes Cluster
                                   +---------------------------------------------+
                                   |                               POD           |
                                   |                           +---------+       |
                                   |                    +------>  NGINX  |       |
                                   |                    |      +---------+       |
                                   |           LB       |                        |
             +--------------+      |    +---------------+          POD           |
0.0.0.0:32643|  Kube Proxy  |80    |    |               |      +---------+       |
        <------------------>----------->+    SERVICE    +------>  NGINX  |       |
             |              |      |  80|               |      +---------+       |
             +--------------+      |    +---------------+                        |
                   HOST            |                    |          POD           |
                                   |                    |      +---------+       |
                                   |                    +------>  NGINX  |       |
                                   |                           +---------+       |
                                   +---------------------------------------------+

Stateless workloads

Deployments and Replicasets that we had deployed so far are stateless workloads.
There is no state related information stored at Pods/Service, so request from kube-proxy via serivce resource can be routed to any of the Pod in the cluster.
This constitutes stateless workload.
Next section is to create a Stateful workload.

Stateful workloads

Preserve the state of data present on Pods.
Two situations can be possible:
- Multi pod stateful workload
  - If multiple pods are connecting to stateful workload, there should be worker based synchronization
  - Else, stateful data may go out of sync.
- Single pod stateful workload
  - Create persitant volumes
  - Create persitant volume claims to access persitant volumes in a synchronized way, just to prevent ensure data atomicity.

Persistent Volumes

PV are like volumes in Docker, just that their lifecycle is independent of Pods.
This is an API object. Captures details about storage implementation.
Provised by Kubernetes administrator.
Way to abstract storage resource.

Create a persistent volume for MySQL server. File

kind: PersistentVolume
apiVersion: v1
metadata:
  name: pv
  labels:
    type: local
spec:
  storageClassName: manual
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteOnce
  hostPath:
    path: "/data"

This spec specifies the volume is at /data on cluster's node. Apply it : kubectl apply -f pv.yml

root@vagrant:/home/vagrant/kubedata# kubectl get pv
NAME   CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM   STORAGECLASS   REASON   AGE
pv     5Gi        RWO            Retain           Available           manual                  62s

Persistent Volume Claims

Storage requeest by a user.
PVCs consume PV resources.
Way to access abstract storage.
PVC can request specific size and access mode: ReadWriteOnce, ReadOnlyMany, ReadWriteMany

Access Mode	Meaning
ReadWriteOnce	volume can be mounted as read-write by a single node
ReadOnlyMany	volume can be mounted read-only by many nodes
ReadWriteMany	volume can be mounted as read-write by many nodes

Create a PVC spec. File

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: pv-claim
spec:
  storageClassName: manual
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi

Apply it.

root@vagrant:/home/vagrant/kubedata# kubectl apply -f pv-claim.yml
persistentvolumeclaim/pv-claim created

root@vagrant:/home/vagrant/kubedata# kubectl get pvc
NAME       STATUS   VOLUME   CAPACITY   ACCESS MODES   STORAGECLASS   AGE
pv-claim   Bound    pv       5Gi        RWO            manual         8s

root@vagrant:/home/vagrant/kubedata# kubectl describe pvc pv-claim
Name:          pv-claim
Namespace:     default
StorageClass:  manual
Status:        Bound
Volume:        pv
Labels:        <none>
Annotations:   pv.kubernetes.io/bind-completed: yes
               pv.kubernetes.io/bound-by-controller: yes
Finalizers:    [kubernetes.io/pvc-protection]
Capacity:      5Gi
Access Modes:  RWO
VolumeMode:    Filesystem
Mounted By:    <none>
Events:        <none>
root@vagrant:/home/vagrant/kubedata#

Pods use PersistentVolumeClaims to request physical storage
After creating the PersistentVolumeClaim, the Kubernetes control plane looks for a PersistentVolume that satisfies the claim's requirements. If the control plane finds a suitable PersistentVolume with the same StorageClass, it binds the claim to the volume.

Lets create a POD which will use PV as Volume using PVC. File

apiVersion: v1
kind: Pod
metadata:
  name: nginx-pod-with-pvc
spec:
  volumes:
    - name: nginx-pv-storage
      persistentVolumeClaim:
        claimName: pv-claim
  containers:
    - name: nginx-with-pv
      image: nginx
      volumeMounts:
        - mountPath: "/usr/share/nginx/html"
          name: nginx-pv-storage

root@vagrant:/home/vagrant/kubedata# kubectl get pods nginx-pod-with-pvc
NAME                 READY   STATUS    RESTARTS   AGE
nginx-pod-with-pvc   1/1     Running   0          16s

root@vagrant:/home/vagrant/kubedata# kubectl exec -it nginx-pod-with-pvc -c nginx-with-pv -- /bin/bash
root@nginx-pod-with-pvc:/# curl localhost
Hi PV

The file we just created in storage is made accessible to Nginx POD.

Summary

                                +--------------------------------------+
                                |     +------------+                   |
                                |     |    POD     |        +--------------->
                                |     +-----+------+        |          |    |
                                |           |               |          |    |
                                |           |         +-----+------+   |    v
                                |           |         |     PV     |   |   /data
                                |           |         +------+-----+   |
                                |     +-----v------+         ^         |
                                |     |    PVC     +---------+         |
                                |     +------------+                   |
                                |                                      |
                                +--------------------------------------+

PV to PVC bind is automatic, based on storage class.
Pod/Deployment/K8s-Resource link to PVC has to has to be done manually in spec file.

Sample Application Example

This End to End setup will include:
MySQL setup through PV and PVC.
Building Custom Dockerfile for sprinboot application.
Creating Deployment for SpringBoot application. 1. Setup the environment for application to connect to DB. 2. Setting up PVC setup in deployment. 3. Creating Serivce for springboot application access outside pod.
1. Service setup through LB

Once we create spec.yml in bits, we will create a big spec to show our Infrastructure as a Code and deploy that 😄.

MySQL Resource

Step 1: Create PV for MYSQL DB

kind: PersistentVolume
apiVersion: v1
metadata:
  name: mysql-pv
  labels:
    type: local
spec:
  storageClassName: manual
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteOnce
  hostPath:
    path: "/data/mysql"

Step 2: Create PVC for PV

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: mysql-pvc
spec:
  storageClassName: manual
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi

Step 3: Create MySQL deployment Spec

apiVersion: apps/v1 
kind: Deployment
metadata:
  name: dbserver
  labels:
    app: dbserver
spec:
  selector:
    matchLabels:
      app: dbserver
  template:
    metadata:
      labels:
        app: dbserver
    spec:
      containers:
      - image: mysql
        name: mysql
        imagePullPolicy: Never
        env:
        - name: MYSQL_ROOT_PASSWORD
          value: mysecretpassword
        ports:
        - containerPort: 3306
          name: dbserver
        volumeMounts:
        - name: mysql-persistent-storage
          mountPath: /var/lib/mysql
      volumes:
      - name: mysql-persistent-storage
        persistentVolumeClaim:
          claimName: mysql-pvc

Once the DB server is up, please go adhead and login to MySQL and create peopledb for sprinboot application to access.
- mysql -- mysql -u root -pmysecretpassword & create database peopledb

Step 4: Expose MySQL server via Service

apiVersion: v1
kind: Service
metadata:
  name: dbservice
spec:
  selector:
    app: dbserver
  ports:
  - protocol: TCP
    port: 3306
    targetPort: 3306

This will expose this service over/inside cluster for other services to access.

Springboot Application

Step 1: Build and Deploy AppServer

Build the Docker image with name appserver from this File.
```
docker build  -t appserver .
```

Create Deployment spec for appserver.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: appserver
spec:
  replicas: 1
  selector:
    matchLabels:
      app: appserver
  template:
    metadata:
      labels:
        app: appserver
    spec:
      containers:
      - name: appserver
        image: appserver
        imagePullPolicy: Never
        env:
        - name: DB_HOST
          value: dbservice

Step 2: Expose AppServer service via Service type LB to host.

apiVersion: v1
kind: Service
metadata:
  name: contacts
spec:
  type: LoadBalancer
  selector:
    app: appserver
  ports:
  - protocol: TCP
    port: 80
    targetPort: 8080

Infrastructure as a Code

MySQL Full Spec

You can find the full spec file here : File

kind: PersistentVolume
apiVersion: v1
metadata:
  name: mysql-pv
  labels:
    type: local
spec:
  storageClassName: manual
  capacity:
      storage: 5Gi
  accessModes:
    - ReadWriteOnce
  hostPath:
    path: "/data/mysql"   

---
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: mysql-pvc
spec:
  storageClassName: manual
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi

---
apiVersion: apps/v1 
kind: Deployment
metadata:
  name: dbserver
  labels:
    app: dbserver
spec:
  selector:
    matchLabels:
      app: dbserver
  template:
    metadata:
      labels:
        app: dbserver
    spec:
      containers:
      - image: mysql
        name: mysql
        imagePullPolicy: Never
        env:
        - name: MYSQL_ROOT_PASSWORD
          value: mysecretpassword
        ports:
        - containerPort: 3306
          name: dbserver
        volumeMounts:
        - name: mysql-persistent-storage
          mountPath: /var/lib/mysql
      volumes:
      - name: mysql-persistent-storage
        persistentVolumeClaim:
          claimName: mysql-pvc
---
apiVersion: v1
kind: Service
metadata:
  name: dbservice
spec:
  selector:
    app: dbserver
  ports:
  - protocol: TCP
    port: 3306
    targetPort: 3306

kuebctl apply -f mysql-spec.yml 😄

AppServer Full Spec

You can find the full spec file here: File

apiVersion: apps/v1
kind: Deployment
metadata:
  name: appserver
spec:
  replicas: 1
  selector:
    matchLabels:
      app: appserver
  template:
    metadata:
      labels:
        app: appserver
    spec:
      containers:
      - name: appserver
        image: appserver
        imagePullPolicy: Never
        env:
        - name: DB_HOST
          value: dbservice

---
apiVersion: v1
kind: Service
metadata:
  name: contacts
spec:
  type: LoadBalancer
  selector:
    app: appserver
  ports:
  - protocol: TCP
    port: 80
    targetPort: 8080

Quickly apply it with kubectl apply -f appserver-spec.yml

Understanding Advance Kubernetes Resources

Namespace

Namespace are software level cluster virtualization over same physical k8s cluster.

  root@vagrant:/home/vagrant# kubectl get ns
  NAME              STATUS   AGE
  default           Active   19d
  kube-node-lease   Active   19d
  kube-public       Active   19d
  kube-system       Active   19d

Kubernetes starts with 4 namespaces:

default: The default namespace for objects with no other namespace.
kube-system: The namespace for objects created by the Kubernetes system.
kube-public: This namespace is created automatically and is readable by all users (including those not authenticated). This namespace is mostly reserved for cluster usage, in case that some resources should be visible and readable publicly throughout the whole cluster. The public aspect of this namespace is only a convention, not a requirement.
kube-node-lease: This namespace for the lease objects associated with each node which improves the performance of the node heartbeats as the cluster scales.

Get Pods from specific namespace kubectl get pods --namespace=default OR kubectl get pods -n default

root@vagrant:/home/vagrant# kubectl get pods --namespace=kube-system
NAME                              READY   STATUS    RESTARTS   AGE
coredns-f9fd979d6-g9wxg           1/1     Running   5          19d
coredns-f9fd979d6-zrdvs           1/1     Running   5          19d
etcd-vagrant                      1/1     Running   5          19d
kube-apiserver-vagrant            1/1     Running   5          19d
kube-controller-manager-vagrant   1/1     Running   7          19d
kube-flannel-ds-64l2p              1/1     Running   6          19d
kube-proxy-4j4kw                  1/1     Running   5          19d
kube-scheduler-vagrant            1/1     Running   7          19d

Creating Namespace & Adding resource

Create namespace : kubectl create namespace qa

Once the namespace is created, just add the metadata field : namespace: qa, File

apiVersion: v1
kind: Pod
metadata:
   name: nginx
++ namespace: qa
spec:
  containers:
  - name: nginx
    image: nginx

Most Kubernetes resources (e.g. pods, services, replication controllers, and others) are in some namespaces. However namespace resources are not themselves in a namespace. And low-level resources, such as nodes and persistentVolumes, are not in any namespace.
- To see the list of resource not in namespace : kubectl api-resources --namespaced=false

Context

Is a tuple of cluster, user, namespace. This is useful when you connect to multiple clusters from one control plane.

Get the current context: kubectl config get-contexts

root@vagrant:/home/vagrant/kubedata# kubectl config get-contexts
CURRENT   NAME                          CLUSTER      AUTHINFO           NAMESPACE
*         kubernetes-admin@kubernetes   kubernetes   kubernetes-admin

You can create kubernetes context using config file or using commands.

Create a qa-config: kubectl config set-context dev-env --cluster=kubernetes --user=new-admin --namespace=dev-env

root@vagrant:/home/vagrant/kubedata# kubectl config set-context dev-env --cluster=kubernetes --user=new-admin --namespace=dev-env
Context "dev-env" created.

root@vagrant:/home/vagrant/kubedata# kubectl config get-contexts
CURRENT   NAME                          CLUSTER      AUTHINFO           NAMESPACE
         dev-env                       kubernetes   new-admin          dev-env
*          kubernetes-admin@kubernetes   kubernetes   kubernetes-admin

Now use the created context using : kubectl config use-context dev-env
All your k8s resource will now be in DEV name space under kubernetes cluster 😄
- But to create resource you will need user new-admin authentication. This is the user created during context creation.
- Create username & password for user new-admin to use the resource in context and create a role binding: Run this before switching context kubectl config set-credentials new-admin --username=adm --password=changeme
```
cat << EOF | kubectl apply -f -
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: new-admin
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: cluster-admin
subjects:
- apiGroup: rbac.authorization.k8s.io
  kind: User
  name: [email protected]

EOF
```

CheatSheet

I plan to write a simple cheat sheet covering the commands in this repo. But for now Try : k8s-official-cheat-sheet

Next Steps

In detail K8s Reference
API Guide
CLI Guide
K8s Design Docs
Raising a PR makes me happy, take that as a next step.
Issues are more than welcome.
If you like it, share it.

rosehgal/k8s-In-30Mins

rosehgal

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