Kubernetes Objects

Table of contents

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

 

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Pods

 

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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