firstcluster.md

Deploying the first cluster

• Install :

  Minikube :

  Minikube is local Kubernetes, focusing on making it easy to learn and develop for Kubernetes and to create test clusters.

  Kubectl :

  The Kubernetes command-line tool, kubectl, that allows you to run commands against Kubernetes clusters. You can use kubectl to deploy applications, inspect and manage cluster resources, and view logs.

• Create a cluster ლ(｀ー´ლ) :

  PS G:\K8s> minikube.exe -p c1 start
  PS G:\K8s> minikube.exe -p c1 status
  c1
  type: Control Plane
  host: Running
  kubelet: Running
  apiserver: Running
  kubeconfig: Configured

• Creating a test pod :

  PS G:\K8s> kubectl create deployment nginxtest --image=nginx
  deployment.apps/nginxtest created
  PS G:\K8s> kubectl.exe get pod
  NAME                        READY   STATUS              RESTARTS   AGE
  nginxtest-d487d74db-4jqbb   0/1     ContainerCreating   0          3s
  PS G:\K8s> kubectl.exe get pod
  NAME                        READY   STATUS    RESTARTS   AGE
  nginxtest-d487d74db-4jqbb   1/1     Running   0          2m21s

• Deployments and replicas :

  PS G:\K8s> kubectl.exe describe deployment nginx
  Name:                   nginxtest
  Namespace:              default
  CreationTimestamp:      Sun, 13 Feb 2022 01:54:40 +0530
  Labels:                 app=nginxtest
  Annotations:            deployment.kubernetes.io/revision: 1
  Selector:               app=nginxtest
  Replicas:               1 desired | 1 updated | 1 total | 1 available | 0 unavailable
  StrategyType:           RollingUpdate
  MinReadySeconds:        0
  RollingUpdateStrategy:  25% max unavailable, 25% max surge
  Pod Template:
    Labels:  app=nginxtest
    Containers:
     nginx:
      Image:        nginx
      Port:         <none>
      Host Port:    <none>
      Environment:  <none>
      Mounts:       <none>
    Volumes:        <none>
  Conditions:
    Type           Status  Reason
    ----           ------  ------
    Available      True    MinimumReplicasAvailable
    Progressing    True    NewReplicaSetAvailable
  OldReplicaSets:  <none>
  NewReplicaSet:   nginxtest-d487d74db (1/1 replicas created)
  Events:
    Type    Reason             Age    From                   Message
    ----    ------             ----   ----                   -------
    Normal  ScalingReplicaSet  4m25s  deployment-controller  Scaled up replica set nginxtest-d487d74db to 1
  
  PS G:\K8s> kubectl.exe get replicaset
  NAME                  DESIRED   CURRENT   READY   AGE
  nginxtest-d487d74db   1         1         1       3m53s

• Edit deployments :
  • Let's have 2 replicas of nginx :

  PS G:\K8s> kubectl.exe edit deployment nginxtest
  deployment.apps/nginxtest edited
  PS G:\K8s> kubectl.exe describe deployment nginx | findstr /i replicas:
  Replicas:               2 desired | 2 updated | 2 total | 2 available | 0 unavailable
  PS G:\K8s> kubectl.exe get pod
  NAME                        READY   STATUS    RESTARTS   AGE
  nginxtest-d487d74db-4jqbb   1/1     Running   0          14m
  nginxtest-d487d74db-prqmb   1/1     Running   0          20s
  PS G:\K8s> kubectl.exe get replicaset
  NAME                  DESIRED   CURRENT   READY   AGE
  nginxtest-d487d74db   2         2         2       17m

  • Similarly you can change other components like image version etc.
• Creating and accessing a container :
  • Uggh the container crashed.
  • Understand CrashLoopBackOff :

  PS G:\K8s> kubectl create deployment ubuntu-test --image=ubuntu:latest
  deployment.apps/ubuntu-test created
  PS G:\K8s> kubectl.exe get pods
  NAME                           READY   STATUS              RESTARTS   AGE
  ubuntu-test-85c8959887-ztrgg   0/1     ContainerCreating   0          3s
  PS G:\K8s> kubectl.exe get pods
  NAME                           READY   STATUS             RESTARTS     AGE
  ubuntu-test-85c8959887-ztrgg   0/1     CrashLoopBackOff   1 (7s ago)   16s

  • Lets see whats happening in the pod :

      PS G:\K8s> kubectl.exe describe pod ubuntu-test-85c8959887-ztrgg
  Name:         ubuntu-test-85c8959887-ztrgg
  Namespace:    default
  Priority:     0
  Node:         c1/172.18.156.98
  Start Time:   Sun, 13 Feb 2022 16:42:51 +0530
  Labels:       app=ubuntu-test
                pod-template-hash=85c8959887
  Annotations:  <none>
  Status:       Running
  IP:           172.17.0.3
  IPs:
    IP:           172.17.0.3
  Controlled By:  ReplicaSet/ubuntu-test-85c8959887
  Containers:
    ubuntu:
      Container ID:   docker://2e856bad136f97be9d464209216d40155b5b34d265ddfc6f6ab159d472f24250
      Image:          ubuntu:latest
      Image ID:       docker-pullable://ubuntu@sha256:669e010b58baf5beb2836b253c1fd5768333f0d1dbcb834f7c07a4dc93f474be
      Port:           <none>
      Host Port:      <none>
      State:          Waiting
        Reason:       CrashLoopBackOff
      Last State:     Terminated
        Reason:       Completed
        Exit Code:    0
        Started:      Sun, 13 Feb 2022 16:43:19 +0530
        Finished:     Sun, 13 Feb 2022 16:43:19 +0530
      Ready:          False
      Restart Count:  2
      Environment:    <none>
      Mounts:
        /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-pjgqw (ro)
  Conditions:
    Type              Status
    Initialized       True
    Ready             False
    ContainersReady   False
    PodScheduled      True
  Volumes:
    kube-api-access-pjgqw:
      Type:                    Projected (a volume that contains injected data from multiple sources)
      TokenExpirationSeconds:  3607
      ConfigMapName:           kube-root-ca.crt
      ConfigMapOptional:       <nil>
      DownwardAPI:             true
  QoS Class:                   BestEffort
  Node-Selectors:              <none>
  Tolerations:                 node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
                               node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
  Events:
    Type     Reason     Age                From               Message
    ----     ------     ----               ----               -------
    Normal   Scheduled  48s                default-scheduler  Successfully assigned default/ubuntu-test-85c8959887-ztrgg to c1
    Normal   Pulled     43s                kubelet            Successfully pulled image "ubuntu:latest" in 4.008007591s
    Normal   Pulled     39s                kubelet            Successfully pulled image "ubuntu:latest" in 3.972582861s
    Normal   Pulling    24s (x3 over 47s)  kubelet            Pulling image "ubuntu:latest"
    Normal   Created    20s (x3 over 43s)  kubelet            Created container ubuntu
    Normal   Started    20s (x3 over 43s)  kubelet            Started container ubuntu
    Normal   Pulled     20s                kubelet            Successfully pulled image "ubuntu:latest" in 4.036496621s
    Warning  BackOff    6s (x4 over 38s)   kubelet            Back-off restarting failed container

  • It took me a while to get my head around this, but, I think since it is the nature of a container to close when the task is done, the container creates and shuts itself down (maybe something like "docker run -dit" was needed?), since there were no actions/tasks/commands really specified in the deployment. We will debug this some other day.
  • Lets try running a different container and then access it :

  PS G:\K8s> kubectl.exe create deployment mongodbtest --image=mongo
  deployment.apps/mongodbtest created
  PS G:\K8s> kubectl.exe get pod -w
  NAME                          READY   STATUS              RESTARTS   AGE
  mongodbtest-b955d8c76-4mhqs   0/1     ContainerCreating   0          8s
  mongodbtest-b955d8c76-4mhqs   1/1     Running             0          2m12s
  PS G:\K8s> kubectl.exe exec -it mongodbtest-b955d8c76-4mhqs -- /bin/bash
  root@mongodbtest-b955d8c76-4mhqs:/#

  The double dash symbol "--" is used to separate the command you want to run inside the container from the kubectl arguments.

  root@mongodbtest-b955d8c76-4mhqs:/# ls
  bin   data  docker-entrypoint-initdb.d  home        lib    lib64   media  opt   root  sbin  sys  usr
  boot  dev   etc                         js-yaml.js  lib32  libx32  mnt    proc  run   srv   tmp  var
  root@mongodbtest-b955d8c76-4mhqs:/# hostname
  mongodbtest-b955d8c76-4mhqs

• You can also manually create/delete a deployment and then deploy it using :

  PS G:\K8s> kubectl.exe apply -f deploymentfilename.yaml
  PS G:\K8s> kubectl.exe delete -f deploymentfilename.yaml

• Similarly kubectl can be used with services, volumes etc.