This writing is about my learning with kubernetes. This blog might be a quick look for my day to day uses with kubernetes. Hope you like it 🤌

Kubernetes Workload

• An app in k8
• Pod is atomic workload
• Replicaset
• Deployment
• StatefulSet
• DeamonSet
• Task that run to completion
  • Job
  • CronJob

> kubectl get all
> We can ssh into kubernetes node

Kubernetes Pods

• App is in docker hub as docker image
• Kubernetes cluster is already setup

Pod

• Is a single instance of an application
• Smallest object that can be created in Kubernetes
• Has 1:1 relationship with your application (mostly)

Multi-container pods

• Helper container like scenario
• When we want to keep up
• Same network space and localhost connection and the same storage space.

To deploy container

# kubectl running nginx pod simple
kubectl run nginx —image nginx

# get the status of all the pods in the system
kubectl get pods

Minikube Workshop

### MINIKUBE DEMO

# Create a deployment
kubectl create deployment hello-minikube --image=k8s.gcr.io/echoserver:1.10

# To get all the deployments
kubectl get deployments

# Expose deployment uisng nodeport --port=8000
kubectl expose deployment hello-minikube --type=NodePort --port=8080
service/hello-minikube exposed

Pod Workshop

### Pods Workshop

# requires imge to use it
kubectl run nginx --image=nginx

# kubectl get pods to get the  pods
kubectl get pods

Containers will be creating to created state

kubectl describe pod <pod_name> # is more detailed compared to get pod

• Learn more about describe

  • Events
    • All the events which ran after the creation of pod
  • Containers

  

Making pod using YAML in kubernetes

## This must be named pod-defination.yml file

apiVersion: v1 # Version of kubernetes api # Depends upon which we want to make
kind: Pod # POD, Service, ReplicaSet, Deployment
metadata:
  name: myapp-pod
  labels: # custom keyvalue pair put any thing you want
  app: myapp
  type: front-end
spec:
  containers:
    - name: nginx-container
      image: nginx # name of docker image in image repo

Kubernetes ReplicationControllers and ReplicaControlSet

• To run more than one pod in the node.
• Ensures that the required setup is met for number of pods
• For load balancing and Scaling

Replication Controller vs Replica set

Replication Controller:

• older tech
• replaced by replica set

Kubernetes Replicasets[ In depth ]

• Primary method of managing pod replicas and their lifecycle to provide self-healing capabilities
• Their job is to always ensure the desired number of pods are running

# Replication Controller

apiVersion: v1
kind: ReplicationController
metadata:
  name: myapp-rc
  labels:
    app: myapp
    type: front-end
spec:
  replicas: 3

  template:        # As same as for pod
    metadata:
      name: myapp-pod
      labels:
        app: myapp
    spec:
      containers:
      - name: nginx-container
        image: nginx

# Replication-set Controller

apiVersion: apps/v1
kind: ReplicationController
metadata:
  name: myapp-rc
  labels:
    app: myapp
    type: front-end
spec:
  replicas: 3
  selector:        # major difference
		 matchLabels:
		   type: myapp # matching the myapp

  template:        # As same as for pod
    metadata:
      name: myapp-pod
      labels:
        app: myapp
    spec:
      containers:
      - name: nginx-container
        image: nginx

Kubernetes Deployment

• For production
• For updates: Blue green, Rolling, Rollback etc
• Object higher than replica-set
• Create on template for each microservice

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:

  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80

  replicas: 3
  selector:
    matchLabels:
      app: nginx

Updates

• Changes replicaset from 5 to 0 in old version
• Changes replicaset from 0 to 5 in new version
• And vice versa in rollback

Kubernets DaemonSet

• Ensure all nodes (or a subset) run an instance of a Pod
• Scheduled by the scheduler controller and run by the daemon controller
• As nodes are added to the cluster, Pods are added to them
• Typical uses
  • Running a cluster storage daemon
  • Running a logs collection daemon on every node
  • Running a node monitoring daemon on every node

Kubernetes StatefulSet

• For Pods that must persist or maintain state

Kubernetes Networking

• Kubernetes doesn’t setup any networking for us
• We should setup networking ourself
• KUBERNETES EXPTECTS THIS
  • All PODs can communicate to one another without NAT
  • All nodes can communicate with al containers and vice versa without NAT

Kubernetes Services

• Services enables connectivity between various parties
• Loose coupling between microservices
• Connection between FE to BE, Users to FE, etc

NodePort

• Listens to the port and forwards it to node port

ClusterIP

Kubernetes Namespaces

Kubernetes Job

Cronjob In UTC

Storage and Persistent volume data

Volumes

Storage - Static Way

• Persistent Volumes
  • Represnts a storage resource
  • Cluster wide
  • Provisoned by an admin
• Persistent Volume Claim
  • A one to one mapping to persistent volume
• One or more pods can use a persistent volume Claom
• Can be consumed by any of the conatiners within the pod

Drawback

• Can lead to waste of resources

Persistent volumes and claims

Reclaim Policies

• Delete
  • Delete the data upon pods deletion
  • The default
• Retain
  • Keeps the data upon pods deletion

Kubernetes ConfigMaps

Kubernetes Secrets

Kubernetes Observability - Probes

Kubernetes HPA