DevOps Classroomnotes 12/Dec/2022

Horizontal Pod Autoscaler

• This allows to autoscale pods based on metrics
• Refer Here for offical docs
• Refer Here for the changes
  
  

Scheduling in K8s using taints and tolerations

• There are certain cases where you would want to run a pod on specific set of nodes.
• Refer Here
• Refer Here for the article on taints and tolerations
• Lets taint some node with poc

kubectl taint nodes <node-name> poc=true:NoSchedule

#aws
kubectl taint nodes ip-10-0-1-119.us-east-2.compute.internal poc=true:NoSchedule
for other nodes
kubectl taint nodes ip-10-0-1-199.us-east-2.compute.internal poc=false:NoSchedule

kubectl taint nodes ip-10-0-3-230.us-east-2.compute.internal poc=false:NoSchedule


# azure
kubectl taint nodes aks-nodepool1-42348830-vmss000000 poc=true:NoSchedule

• Ensure all the nodes are tainted and then apply
• Refer Here for the changes done in the Pod to tolerate the taint on the node
  
• You can also schedule Pods on specific node by nodeSelector property in Pod spec which matches exact labels

---
apiVersion: v1
kind: Pod
metadata:
  name: node-selector
spec:
  nodeSelector:
    beta.kubernetes.io/os: linux
  containers:
    - image: nginx:1.23
      name: nginx-container
      ports:
        - containerPort: 80

Annotations

• Annotations are also key value pairs, they are used by the tools i.e. aks or eks to extend functionality
• Refer Here for offical docs
• azure ingress annotations Refer Here
• AWS Loadbalancer annotations Refer Here
• Lets use annotations to create internal load balancer in azure

---
apiVersion: v1
kind: Service
metadata:
  name: nginx-svc-lb
  annotations:
    service.beta.kubernetes.io/azure-load-balancer-internal: "true"
spec:
  type: LoadBalancer
  selector:
    app: nginx
  ports:
    - name: webport
      port: 35000
      targetPort: 80

• In AWS

apiVersion: v1
kind: Service
metadata:
  name: nginx-svc-lb
  annotations:
    kubernetes.io/role/internal-elb: "1"
spec:
  type: LoadBalancer
  selector:
    app: nginx
  ports:
    - name: webport
      port: 35000
      targetPort: 80

Ingress and Ingress Controller

• Ingress in Layer 7 load balancer.
• When we need path based or hostname based routing we can use ingress.
• Ingress supports layer7 lb with in k8s cluster but to expose this functionality outside of k8s cluster it needs ingress controller.
• k8s doesnot have default ingress controller.
• There are many free ingress controller
  • nginx ingress controller
  • haproxy ingress controller
  • contour ingress controller
• All the cloud providers have layer 7 lb they support cloud specific ingress controller
  • aws supports application load balancer ingress controller
  • azure supports application gateway ingress controller.
• azure aks ingress controller

apiVersion: v1
kind: Pod
metadata:
  name: aspnetapp
  labels:
    app: aspnetapp
spec:
  containers:
  - image: "mcr.microsoft.com/dotnet/core/samples:aspnetapp"
    name: aspnetapp-image
    ports:
    - containerPort: 80
      protocol: TCP

---

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

---

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: aspnetapp
  annotations:
    kubernetes.io/ingress.class: azure/application-gateway
spec:
  rules:
  - http:
      paths:
      - path: /
        backend:
          service:
            name: aspnetapp
            port:
              number: 80
        pathType: Exact

• Refer Here
•