What is Kubernetes

Orchestrates the placement (scheduling) and execution of application containers within and across computer clusters.

The abstractions in Kubernetes allow you to deploy containerized applications to a cluster without tying them specifically to individual machines.

What is containerization

To make use of this new model of deployment, applications need to be packaged in a way that decouples them from individual hosts: they need to be containerized.

Kubernetes automates the distribution and scheduling of application containers across a cluster in a more efficient way

Control Plane coordinates the cluster.

Nodes are the workers that run applications.

Commands

# see which k8 pods are running
kubectl describe pods

## You can optionally pass a pod name
kubectl describe pods pod_name

# get events
## this will show the issue why pod has not been scheduled
kubectl get events

# describe issue with pod in detail
kubectl logs pod_name

Errors

ImagePullBackOff

Container running a pod fails to pull the required image from a container registry.

• When a pod is created, k8s attempts to pull the container image specified in the pod definition from the container registry
  • IF the image is not available or cannot be pulled, k8s stops pulling image and pod will remain in a pending state
    • Root cause could be network connectivity, image name/tag, credential freshness, permissions issues

Port Forward

• Port forward exposes the service locally