DevOps Classroomnotes 30/Apr/2023

Deployment

• Deployment is a k8s object which can help in rolling out and rolling back updates
• Deployment controls replica set and replica set controls pods
  
• Lets create a manifest with some application deployment
• apply deployment and service. Access the application
  
  
• Lets get deployment information
  
  
• lets explore rollout command
  
• Refer Here for the manifests used to create revision 1
• Lets update the specs to change image from nginx to httpd Refer Here for changes in manifests
  
  
  
• Now to rollback to previous versions and update multiple versions kubectl rollout undo
  
• The change-cause is showning as none which is not good. What can be done to have a valid change cause.

Annotations

• Refer Here for official docs
• Refer Here for the manifest with change cause annotation
  
• Refer Here for some annotations specific to azure aks ingress
• Refer Here for some annotations specific to aws eks ingress

DaemonSet

• DaemonSet is a controller which creates pod on every/selected nodes in k8s cluster
• Use cases:
  • log collectors
  • agents etc
• Refer Here for official docs
• Refer Here for the manifests for daemonsets
  

Scheduling Pods

• possible ways
  
• Refer Here for assigning pods to nodes

Node Selectors

• We have added manifests with pod and service. Refer Here for manifests
• Now lets select node by its name Refer Here
  
• We have two nodes lets attach the following labels
  • node 0: purpose: poc
  • node 1: purpose: testing
• When we have tried to create a pod with nodeSelector matching purpose: poc it was created on node 0 and when we created a pod with purpose: testing it created in node 1 and when created a pod with purpose: development it was in pending state (not created)

---
apiVersion: v1
kind: Pod
metadata:
  name: nodeselector
  labels:
    app: nginx
    purpose: nodeselector
spec:
  nodeSelector:
    purpose: testing
  containers:
    - name: jenkins
      image: jenkins/jenkins:jdk11
      ports:
        - containerPort: 8080

Affinity/Anti Affinity Based

• Refer Here for official docs

Taints and Tolerations

• Refer Here for official docs

Headless Service

• Refer Here
• Headless service will not have cluster ip
  
• headless service spec

---
apiVersion: v1
kind: Service
metadata:
  name: nginx-svc
spec:
  selector:
    app: nginx
  type: ClusterIP
  clusterIP: None
  ports:
    - name: nginx-svc
      port: 80
      targetPort: 80
      protocol: TCP

• Headless service returns the ips of the pods returned by selector.
• This is used in stateful sets