Kubernetes - Notes and Commands

Kubernetes.md

Kubernetes

• It's a container orchestration
  • Many servers act like one
• Released in 2015
• Runs on top of Docker
• Provides CLI/API to manage container across servers
  • kubectl
• Services
  • Clouds: Google Engine, etc
• Many vendors with a "custom distribution"

Why orchestration?

• Not every solution needs orchestration
• Orchestration is designed to automate changes and monitor the state of things
• Another alternative: Docker Swarm
• Distributions:
  • Docker Enterprise
  • Rancher
  • OpenShift
  • Canonical
  • VMWare PKS
• Custom vendor distributions pack other tools with Kubernetes
• Most distributions are up to date with the official Kubernetes

Kubernetes vs Docker Swarm

• Swarm
  • is easy to deploy/manage
  • comes with Docker
  • 80/20 rule: has 20% of features of Kubernetes for 80% of the use cases
  • it runs anywhere Docker runs
  • secure by default
  • easier to troubleshoot
• Kubernetes
  • has more features and it's more flexible
  • clouds deploy/manage it for you
  • multiple distributions
  • widest adoption and community
  • flexible

Kubernetes Architecture

• Kubernetes: the whole orchestration system
  • K8s or Kube for short
• Kubectl: CLI to configure Kubernetes and manage apps
  • "cube control" => official pronunciation
• Node: single server in the Kubernetes cluster
• Kubelet: Kubernetes agent running on nodes
• Control Plane: Set of containers that manage the cluster
  • Includes API server, scheduler, controller managed, etcd, etc.
  • Sometimes called "master"
• Pod: one or more containers running together on one node
  • Basic unit of deployment
• Controller: for creating/updating pods and other objects
  • Many types:
    • Deployment
    • ReplicaSet
    • StatefulSet
    • DaemonSet
    • Job
    • CronJob
• Service: network endpoint to connect to a pod
  • A stable address for pod(s)
  • Created on top of existing pods
  • CoreDNS: allow us to resolve services by name
  • Types of services:
    • ClusterIP (default):
      • only reachable from within the cluster (nodes and pods)
      • single, internal virtual IP allocated
      • pods can reach service on apps port number
    • NodePort:
      • high port allocated on each node
      • port is open on every node's IP
      • anyone can connect (if they can reach the node)
      • other pods neet to be updated to this port
    • LoadBalancer:
      • mostly used on the cloud
      • controls a load balancer endpoint external to the cluster
      • only available when infra provider gives you a load balancer
      • creates CreatePort + ClusterIP services, tells load balancer to send to NodePort
    • ExternalName:
      • Adds CNAME DNS record to CoreDNS only
      • Not used for Pods, but giving pods a DNS name to use for something outside Kubernetes
    • Kubernetes Ingress: ???
• Namespace: filtered group of objects in cluster

Commands

• kubectl version
• kubectl run
  • Creates the pod, the replicaset and the deployment
  • Default command gives only 1 replica
• kubectl create
• kubectl apply
• kubectl scale deploy/my-apache --replicas 2

Examples

• kubectl run my-nginx --image nginx
• kubectl run my-apache --image httpd
• kubectl run httpenv --image bretfisher/httpenv
• kubectl get service
  • Look up what IP was allocated
    • Only accessible inside the cluster (you'll see no external IP address filled)
• kubectl get pods
  • kubectl get pods -w
• kubectl get all
• kubectl delete deployment my-nginx
• kubectl scale deploy/my-apache --replicas 2
  • kubectl scale deployment my-apache --replicas 2
• kubectl logs deployment/my-apache
  • kubectl logs deployment/my-apache --follow --tail 1
• kubectl logs -l run=my-apache: Filter logs by deployment label
• kubectl describe pod/my-apache-6b4dc47d85-7f9m9
• kubectl delete pod/my-apache-6b4dc47d85-7f9m9
  • It'll trigger the controller so it'll make sure it the specified replicas running
• kubectl expose: creates a service for existing ports. It's a way to expose them to the outside world
• kubectl expose deployment/httpenv --port 8888
• kubectl run --generator=run-pod/v1 tmp-shell --rm -it --image bretfisher/netshoot -- bash
  • curl -X GET httpenv:8888
• kubectl expose deployment/httpenv --port 8888 --name httpenv-np --type NodePort
  • curl -X GET localhost:32088
• kubectl expose deployment/httpenv --port 8888 --name httpenv-lb --type LoadBalancer
  • curl -X GET localhost:8888
• kubectl delete services/httpenv services/httpenv-np services/httpenv-lb
• kubectl delete deployment/httpenv