Replication Controller

• Replication Controller is the first gen replica workload for k8s objects.
• Replication Controller labels can be matched only on equality not set based Refer Here

Replica Set

• This is succesor to Replication Controller.
• Replica Sets are used by Deployments.
• Replica Sets changes can be tracked and that is what the deployment uses.
• Refer Here for the official docs
• Lets create a replicaset with 4 nginx Pods. Refer Here for the changes
  
• k8s replica set will always try to maintain the desired count. Of the desired is not matching with actual state, a new Pods can be created or existing pods can be deleted to maintain the desired state
• Scaling number of replicas
  • imperative way:
    
  • declartive way: Change the spec and apply the spec again.
    
• Exercise: Create a replica set with Pod specification with jenkins Pod and ping -c 4 google.com in alpine as init container with restart policy Never.
• Refer Here for the changeset
  
• top commands using kubectl (Need to fix metrics server)
  • metrics server needs to be added to k8s cluster Refer Here
• kubernetes UI: Refer Here (Need to work with tokens and proxy)
• Terms to understand
  • addons
  • users
  • service account
  • cluster role binding
• Next Steps
  • Limits to containers
  • Expose applications to outside world
  • Kubernetes as a service (AKS, EKS)
  • Deployments & Other workloads
  • deal with storage
  • Authentication and Authorizations
• Getting inside Containers

kubectl exec -it <pod-name> -- <shell /bin/bash /bin/sh>
kubectl exec <pod-name> -- <linux command>

Kubernetes Service

• Refer Here for official docs
• Overview
  
• Lets use the replica set with 4 nginx replicas and create a cluster ip service which creates an internal ip accesssible within k8s cluster Refer Here
• Create and verify replica set with pods
  
  
• This svc can be verified only by some Pod in k8s cluster. Lets create an experiment pod. Refer Here for the changes
• Check for accessing nginx svc using ip
  
• We are able to access the nginx using svc ip with in cluster
• Now verify with service name inside cluster and it will be working
  
• K8s can expose the service to the external world
  • nodePort: Expose the service to the particular port on all the nodes of k8s cluster
  • loadBalancer: Exposes the service to the loadbalancer
  • external: Creates a DNS record which can be added to DNS servers maintaine by your org.
• Expose the above service to the nodes. Refer Here for the changes
  
• Lets solve this error by changing node port Refer Here