/k8s-notes

Online YAML Lint

http://www.yamllint.com/

Pods

kubectl run nginx --image=nginx

creates a pod ( deployment, without using a definition file)

kubectl get pods -o wide

Replication Controller

kubectl create -f rc-definition.yml

kubectl get replicationcontroller

kubectl get pods

ReplicaSet

selector - is the major difference between Replicaset and Replication controller

kubectl create -f replicaset-definition.yml

kubectl get replicaset

kubectl get pods

kubectl describe replicaset <<replicasetname>>

kubectl delete replicaset <<replicasetname>>

Labels and selectors

ReplicaSet / Replication controller:

  • Can Monitor existing pods already created
  • can create pods
  • it monitors the pods and create them if any one goes down to maintain the desired no. of pods
  • scale up or scale down
    kubectl replace -f replicaset-definition.yml
                  or
    kubectl scale --replcas=6 -f replicaset-definition.yml
                  or
    kubectl scale --replicas=6 replicaset myapp-replicaset
    (replicaset type replicaset name)

Deployments

  • Rolling updates
  • Rollbacks
  • Upgrades
  • Modify resource allocations

kubectl create -f deployment-definition.yml

kubectl get deployments

kubectl get replicaset

kubectl get pods

kubectl get all

rollout and Versioning

Revision 1 - first deployment

Revision 2 - new deployment

status of rollout and history

kubectl rollout status deployment/<<deploymentname>>

kubectl rollout history deployment/<<deploymentname>>

Deployment Strategy:

Recreate:

  • destroy all and create a newer versions Problem with this - application would be down and inaccessible to the user
  • This is a recreation strategy

Rolling update: ( Default strategy)

  • Bring down one and update one
  • no downtime
  kubectl rollout undo deployment/myapp-deployment

brings up the old replicaset one by one and shuts down the pods on new replicaset one by one

observe the behaviour by running

kubectl get replicasets
  • To get record the change cause ( this can be viewed on rollout history)
 kubectl create -f deployment/deployment-definition.yml --record

  kubectl rollout history deployment/myapp-deployment

kubectl apply

upgrading the newer version on deployment file and then

- kubectl apply -f deployment-definition.yml

OR

- kubectl set image deployment/myapp-deployment nginx=nginx:1.9.1

Underthehood - Rolling update strategy, it creates a new replicaset and start taking down the pod one by one on the old replicaset

  • view the replicasets whilst this in progress
  kubectl get replicasets

Some examples

Updating the version -

  • kubectl apply -f deployment/deployment-definition.yml ( OR )
  • kubectl set image deployment/myapp-deployment nginx=nginx:1.12-perl
  • kubectl rollout history deployment/myapp-deployment
  • kubectl rollout undo deployment/myapp-deployment
  • kubectl rollout status deployment/myapp-deployment
  • kubectl rollout history deployment/myapp-deployment

kubernetes networking 101

All containers / PODS can communicate to one another without NAT All nodes can communicate with all containers and vice-versa without NAT

  • Cluster Networking

Services

  • enable communication with varoius components within and outside of the application
  • connect applications together with other applications / users

ssh into the kubernetes node - can curl the pod network ip, would work

Service

  • To listen to a port on node, and forward the request on that port, to a port running the web application on pod

Service Types

  • NodePort
  • ClusterIP
  • LoadBalancer

port on pod - 80 ( Web server running - target port) port on service - 80 (port) port on node - 30008( node port) ( should be within 30000- 32767 range)

  kubectl create -f service-definition.yml

  kubectl get services