Bite-Sized Kubernetes Part 2 - Pods

Arr!☸️

In Part 1 we were introduced to the basics of kubernetes and took a brief look at the k8s "objects".
Onward now with our expedition with Pods, the smallest object in k8s.

OBJECT	DESCRIPTION
👉 Pods	The lowest level, single instance of an application
ReplicaSets	The next level, manages a set of pods
Deployments	The next level, manages a set of ReplicaSets
Services	The next level, manages a set of deployments
Ingress	The next level, manages a set of services
Volumes	The next level, manages a set of ingress
Namespaces	The next level, manages a set of volumes
Cluster	The highest level, manages a set of namespaces

Pods:

• K8s does not deploy the containers directly on the worker nodes.
• The containers are encapsulated into a kubernetes object, known as 'pod'.
• A pod is a single instance of an application.
• Usually a pod contains a single container, but it can contain multiple containers, and these containers are not the same containers.
• For example, a pod can contain a container running the application, and another container running a sidecar process or helper application.
• Containers inside the pod share the same network namespace, and can communicate with each other using localhost, and can share the same storage space.

• Commands:
  

    # deploy a container by creating a pod
    $ kubectl run <pod name> --image=<image name>
  
    # list all pods
    $ kubectl get pods
  
    # list detailed info about all pods
    $ kubectl get pods -o wide
  
    # describe a pod
    $ kubectl describe pod <pod name>  
  
    # delete a pod
    $ kubectl delete pod <pod name>
  

• Creating pods:

  • The .yml file must contain 4 top-level fields/properties i.e. apiVersion, kind, metadata and spec.
  • apiVersion: the version of the k8s API that is being used e.g. v1, apps/v1
  • kind: the type of object that is being created e.g. Pod, Service, Deployment, ReplicaSet
  • metadata: data that helps to uniquely identify the object e.g. name, labels
    • name can only have a string value
    • labels can have any kind of key-value pairs
  • spec: the specification of the object
    • containers: the list of containers that will be launched in the pod
    • name: the name of the container
    • image: the image that will be used to launch the container

  • Example pod-definition.yml:
    

    apiVersion: v1
    kind: Pod
    metadata:
      name: my-pod
      labels:
        app: my-app
        type: my-type
    spec:
      containers:
      - name: my-container
        image: my-image-name:my-image-tag
    

  • Once the .yml file is created, it can be used to create a pod using the kubectl create command:
    

    $ kubectl create -f <file name>.yml
    

  • View detailed info about the pod:
    

    $ kubectl describe pod <pod name>
    

  • Delete the pod:
    

    $ kubectl delete pod <pod name>
    

  • Update the pod with an updated .yml file e.g. with a new image, etc.:
    

    $ kubectl apply -f <file name>.yml
    

Great job sailor!
You now know what pods are, hopefully you found this post an interesting and useful read.
Onwards now to "Controllers and ReplicaSets" in Part 3 which will be out soon!

Haul Wind!!!⛵