Explore Your App

Pods, Nodes, Kubectl main commands

Kubernetes Pods

  • pod: a Kubernetes abstraction that represents one or more application containers (e.g. Docker or rkt) and some shared resources for those containers

    • hosts your application instance

  • Resources include:

    • shared storage, as Volumes

    • networking, as a unique cluster IP address

    • information about how to run each container (e.g. the container image version or specific ports to use)

  • a Pod models an application-specific "logical host"

    • logical host: a logical server environment that acts as the execution environment

    • can contain different application containers that are tightly coupled

      • e.g. it might include a container with your Node.js app and a different container that feeds the data to be published by the Node.js webserver

  • the containers in a Pod share an IP Address and port space

    • containers are co-located and co-scheduled

    • run in a shared context on the same Node

  • pods are the atomic unit on Kubernetes

  • a Deployment on Kubernetes creates Pods with containers inside them (as opposed to creating containers directly)

  • each Pod is tied to the Nod where it is scheduled

    • remains there until termination or deletion

  • if a Node fails, identical Pods are scheduled on other available Nodes in the cluster


  • a Pod always runs on a Node

  • node: a worker machine in Kubernetes that can be a virtual or physical machine, depending on the cluster

    • nodes are managed by the Master

    • can have multiple pods

  • Kubernetes master automatically handles scheduling pods across Nodes in the cluster

  • the Master's automatic scheduling takes into account the available resources on each Node

  • each k8s Node runs at least:

    • Kubelet: a process responsible for communication between the Master and the Node

      • manages the Pods and the containers running on a machine

    • a container runtime (e.g. Docker, rkt) that pulls the container image from a registry, unpacks the container, and runs the application

Troubleshooting with kubectl

  • the following are common operations that can be done with kubectl:

    • kubectl get - list resources

    • kubectl describe - show detailed information about a resource

    • kubectl logs - print the logs from a container in a pod

    • kubectl exec - execute a command from a container in a pod

  • you can use these commands to see when applications were deployed, what their current statuses are, where they are running and what their configurations are

Check application configuration

kubectl get pods - look for existing pods

$ kubectl get pods
NAME                                   READY   STATUS    RESTARTS AGE
kubernetes-bootcamp-765bf4c7b4-2csd9   1/1     Running   0 16s
  • if no pods are running, it means the interactive environment is still reloading its previous state

    • wait a few seconds and list the Pods again

kubectl describe pods - view what containers are inside the Pod and what images are used to build the containers

$ kubectl describe pods
Name:         kubernetes-bootcamp-765bf4c7b4-2csd9
Namespace:    default
Priority:     0
Node:         minikube/
Start Time:   Fri, 17 Jul 2020 15:21:02 +0000
Labels:       pod-template-hash=765bf4c7b4
Annotations:  <none>
Status:       Running
Controlled By:  ReplicaSet/kubernetes-bootcamp-765bf4c7b4
    Container ID:   docker://f0c94d70ca26da1cc4c8e5944d0a6cdab5085e573bf656ab86fb7f8d2851e434
    Image:          gcr.io/google-samples/kubernetes-bootcamp:v1
    Image ID:       docker-pullable://jocatalin/kubernetes-bootcamp@sha256:0d6b8ee63bb57c5f5b6156f446b3bc3b3c143d233037f3a2f00e279c8fcc64af
    Port:           8080/TCP
    Host Port:      0/TCP
    State:          Running
      Started:      Fri, 17 Jul 2020 15:21:06 +0000
    Ready:          True
    Restart Count:  0
    Environment:    <none>
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-2q245 (ro)
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-2q245
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
  Type     Reason            Age                    From    Message
  ----     ------            ----                   ----    -------
  Warning  FailedScheduling  2m33s (x2 over 2m33s)  default-scheduler  0/1 nodes are available: 1 node(s) had taints that the pod didn't tolerate.
  Normal   Scheduled         2m27s                  default-scheduler  Successfully assigned default/kubernetes-bootcamp-765bf4c7b4-2csd9 to minikube
  Normal   Pulled            2m24s                  kubelet, minikube  Container image "gcr.io/google-samples/kubernetes-bootcamp:v1"already present on machine
  Normal   Created           2m23s                  kubelet, minikube  Created container kubernetes-bootcamp
  Normal   Started           2m22s                  kubelet, minikube  Started container kubernetes-bootcamp
  • you can see details about the Pod's container:

    • IP addres

    • ports used

    • list of events related to the life cycle of the pod

Note: the describe command can be used to get detailed information about most of the kubernetes primitives: node, pods, deployments. The describe output is designed to be human readable, not to be scripted against.

Show the app in the terminal

  • pods run in an isolated, private network so you need proxy access to debug and interact with them

  • use the kubectl proxy command to run a proxy in a second terminal window

kubectl proxy - run the proxy

Starting to serve on
  • again, we need to get the Pod name and query the pod through the proxy

export POD_NAME=$(kubectl get pods -o go-template --template '') echo Name of the Pod: $POD_NAME

$ export POD_NAME=$(kubectl get pods -o go-template --template '{{range .items}}{{.metadata.name}}{{"\n"}}{{end}}')
$ echo Name of the Pod: $POD_NAME
Name of the Pod: kubernetes-bootcamp-765bf4c7b4-2csd9
  • to see the output of the application, you can use curl


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