pod

fun fact: the name pod comes from the saying pod of whales, and the entire k8s ecosystem is based on nautical terms. Even Kubernetes is a greek word which means a helmsman who orchestrates the ship, analogous to how k8s orchestrates pods!

differences between pods and containers?

In docker the smallest unit was a container and in k8s it is a pod, what is the difference?

• in docker we had to specify in the cli the type of container we want to create but k8s uses a declarative approach we just mention everything in the yaml file and it achieves the desired state!
• a single pod in k8s can have multiple containers and these container can easily talk to each other as if they are in the same network!

Let’s compare how we can run a container in docker vs K8s:

docker run -d --name docker-example --network bridge -t nginx:latest

apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
  - name: nginx
    image: nginx:1.14.2
    ports:
    - containerPort: 80

kubectl create -f nginx.yaml

things to know

• a pod is the smallest element in a k8s cluster
• a pod is not a container!
• a pod is a collection of containers + other resources!
• a pod can have:
  • single container
  • multi container
  • init container: an init container is a container that needs to run successfully for the pod to run. ex- an init container that checks whether a db connection is set (it can be used to do pre checks needed for a pod to run!)
  • Networking
  • Storage

Note: even though a pod is not a container but the most common pods are single container pods!

Pod related commands:

# runs a pod with a container haivng nginx image!
kubectl run nginx-aniket --image=nginx
 
# definition of the pod - containers, networking storage
kubectl describe pod nginx-aniket
 
# gets pods in the current namespace
kubectl get pods
 
# gets pods in all namespaces
kubectl get pods --all-namespaces

more on interacting with pods

Links:

interacting with pods kubernetes kubectl deployment

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