Kubernetes Objects

Table of contents

• Pods
• Services
  • ClusterIP
  • NodePort
  • LoadBalancer
  • Ingress
    • NGINX Ingress Controller
• Volumes
• Namespaces
• Labels and Selectors

 

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Pods

1. Lets deploy a pod using:

kubectl run nginx

This command will only deploy a Pod on your kubernetes worker node without any container inside it

2. Now lets deploy a pod with a Nginx container

kubectl run nginx --image nginx

This command will only deploy a Pod on your kubernetes worker node with nginx container inside it

3. Get running pod list using

kubectl get pod

4. Get running pod details using:

kubectl describe pod <pod-name>

5. Delete pod using

kubectl delete pod <pod-name>

6. Now lets try to deploy pod with its container using YAML file

Create a pod-definition.yml file

apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
  labels:
    name: myapp-pod
    type: front-end
spec:
  containers:
  - name: nginx-container
    image: nginx

Deploy using following command

kubectl create -f pod-definition.yml

 

ReplicaSet

1. Lets deploy some pod with replication controller using yml file

Create a rs-definition.yml file

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: myapp-replicaset
  labels:
    app: myapp
    type: front-end
spec:
  template:
    metadata:
      name: myapp-pod
      labels:
        app: myapp
        type: front-end
    spec:
      containers:
        - name: nginx-controller
          image: nginx
  replicas: 3
  selector:
    matchLabels:
      type: front-end

Deploy using following command

kubectl create -f rs-definition.yml

2. Get list of replication controller

kubectl get replicationset

3. Get list of Pods

kuberctl get pods

4. You can increase the number of pods by updating the yml definition file then running:

kubectl replace -f rs-definition.yml

5. You can also increase the number of pods by using scale command:

kubectl scale -replicas=6 -f rs-definition.yml

6. Delete replication set using:

kubectl delete replication myapp-rs

 

Deployment

A Deployment provides declarative updates for Pods and ReplicaSets.

You describe a desired state in a Deployment, and the Deployment Controller changes the actual state to the desired state at a controlled rate. You can define Deployments to create new ReplicaSets, or to remove existing Deployments and adopt all their resources with new Deployments.

Create a deployment-definition.yml file

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      name: myapp-pod
      labels:
        app: myapp
    spec:
      containers:
      - name: myapp-container-pod
        image: nginx

1. Lets deploy some pod with deployment using yml file

kubectl create -f deployment-definition.yml

2. Get list of replication controller

kubectl get deployments

3. Get list of Pods

kuberctl get pods

 

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Services

In Kubernetes, there are three general approaches to exposing your application.

• Using a Kubernetes service of type NodePort, which exposes the application on a port across each of your nodes
• Use a Kubernetes service of type LoadBalancer, which creates an external load balancer that points to a Kubernetes service in your cluster
• Use a Kubernetes Ingress Resource

Read more on Medium

 

ClusterIP

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NodePort

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LoadBalancer

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Ingress

 

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Volumes

hostPath

apiVersion: v1
kind: Pod
metadata:
  name: test-pd
spec:
  containers:
  - image: k8s.gcr.io/test-webserver
    name: test-container
    volumeMounts:
    - mountPath: /test-pd
      name: test-volume
  volumes:
  - name: test-volume
    hostPath:
      # directory location on host
      path: /data
      # this field is optional
      type: Directory

 

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Namespaces

1. Get pod details of other namespace using:

kubectl get pods --namespace=dev

2. By below command you will get pod details of default namespace

kubectl get pods

3. You can change default namespace by using:

kubectl config set-context ${kubectl config current-context} --namespace=dev

4. Now for getting pod details of default you need to use

kubectl get pods --namespace=default

5. Get all pods details across namespaces using:

kubectl get pods --all-namespaces

6. Creating a namespace using yml definition:

First, Create a namespace-dev.yml file

apiVersion: v1
Kind: Namespace
metadata:
  name: dev

Now, run the following command:

kubectl create -f namespace-dev.yml

7. Mentioning namespace in pod:

kubectl create -f pod-definition.yml --namespace=dev

8. Get list of system pods using:

kubectl get pods --namespace=kube-system

9. You can set resource limits on namespaces, here an example yml for same:

apiVersion: 1
kind: ResourceQuota
metadata:
 namespace: compute-quota
 namespace: dev
spec:
 hard:
  pods: "10"
  requests.cpu: "4"
  requests.memory: 5Gi
  limits.cpu: "10"
  limits.memory: 10Gi

kubectl create -f compute-quota.yml

 

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Labels and Selectors

 

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