Kubenetes 101

I finially started the learning of K8S, and followed this offical doc to get my pods listed, deployment done, and service created.

0 Cluster

The nodes and control panel concepts are familiar, and k8s can deploy containerized apps into nodes, single or multiple. That’s how it scales out applications.

1 Pods

There are kubelet and docker runtime on each nodes, which is understanding. The Pods are the basic unit of K8S applications and it scales out by pod

2 Basic operations

#alias kc=kubectl
# both singular and plural works
kc get pod/deploy/service
kc describe pods/deployments/services

kc logs "$POD_NAME"
kc exec -it $POD_NAME -- bash

3 Proxy and Service

All pods are internal traffic and not exposed by default. You can either use proxy and services to expose the pods

Assume the app is working on port 8080

# Running proxy 
# you will see "Starting to serve on 127.0.0.1:8001"
kc proxy
# curl 
curl http://localhost:8001/api/v1/namespaces/default/pods/$POD_NAME:8080/proxy/

A Service in Kubernetes is an abstraction which defines a logical set of Pods and a policy by which to access them.

#To create a service 
kc expose deployment/kubernetes-bootcamp --type="NodePort" --port 8080
# Get the port from kc get services/$sevice_name
# 8080:31617/TCP
curl http://localhost:31617"

4 Labels

Use label to easy identify pods

kc label pods "$POD_NAME" version=v1
kc get pods -l version=v1

5 Scale

# Create service with LoadBalancer type
kc expose deployment/kubernetes-bootcamp --type="LoadBalancer" --port 8080

kc scale deployments/kubernetes-bootcamp --replicas=4
# list pods and IP
kc get pod -o wide

6 Update app

Update the application by setting new images to the deployment

kc set image deployments/kubernetes-bootcamp kubernetes-bootcamp=docker.io/jocatalin/kubernetes-bootcamp:v2

kc rollout status deployments/kubernetes-bootcamp
kc rollout undo deployments/kubernetes-bootcamp