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== beto's notes ==
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Kubernetes

These notes are from when I read a bit of Kubernetes Up & Running, so they might be outdated. Recently one of my goals has become to learn Kubernetes more in-depth, as part of it, this will be updated regularly. Date: 2024.08.27

Pods

A Pod is the basic execution unit of a Kubernetes application. Each Pod represents a part of aworkload that is running on your cluster. It represents one or more application containers.

Containers within a Pod share the same IP address and port space; they also run on the same Node.

These containers share resources like:

  • Shared storage, as Volumes
  • Networking, as unique cluster IP address
  • Information about how to run each container, such as the container image version or specific ports to use

Services

A Service is an abstraction which defines a logical set of Pods and a policy by which to access them. They allow loose coupling between dependent Pods.

Services are defined using YAML or JSON, and the targeted Pods are usually determined by a LabelSelector. When selector is not defined, the corresponding Endpoint object won’t be created, also a Label may not be defined when explicitly using type: ExternalName.

Services are also required to expose Pods outside of the Cluster. These Pods can be exposed in different ways depending on the type in the ServiceSpec:

  • ClusterIP (default) - exposes the Service on an internal IP in the cluster. Then the service is only reachable within the Cluster.
  • NodePort - exposes the Service on the same port of each Node in the cluster using NAT. Nodes become available using <NodeIP>:<NodePort>.
  • LoadBalancer - Creates an external load balancer with a fixed external IP to the Service.
  • ExternalName - Maps the Serivce to the contents of the externalName (i.e. foo.bar.example.com).

Control Plane

Coordinates the cluster.

Nodes

A Node is a worker that runs an application and can be a VM or a physical computer. These are managed by the Master and can have multiple Pods.

Each Node runs:

  • A kubelet, an agent for managing the node.
  • A Container Runtime like containerd or docker.

Deployments

Module 2 - Deploy an app

Step 2 - Create a Deployment

1kubectl create deployment kubernetes-bootcamp --image=gcr.io/google-samples/kubernetes-bootcamp:v1
2# Get deployments
3kubectl get deployments
4# Start proxy
5kubectl proxy

Create a deployment

  1. Use kubectl create
1kubectl create deployment hello-node --images=k8s.gcr.io/echoserver:1.4
2# List deployments
3kubectl get deployments
4# List pods
5kubectl get pods
6# List events
7kubectl get events
8# View configuration
9kubectl config view

Create a Service

By default Pods are only accessible by their internal IPs, to expose the Pods you need to create a Service.

  1. Expose the Pod using the kubectl expose command.
1# LoadBalancer indicates this should be exposed outside of the cluster
2kubectl expose deployment hello-node --type=LoadBalancer --port=8080
3# View Services
4kubectl get services
  1. Normally an IP would be used to access the Service, on Minikube it can be accessed with minikube service.
1minikube service hello-node

Cleanup

1kubectl delete service hello-node
2kubectl delete deployment hello-node

Minikube

1minikube version
2minikube start
3kubectl version
4kubectl cluster-info
5kubectl get nodes

Addons

  1. List addons
1minikube addons list
2# Enable metrics-server
3minikube addons enable metrics-server
4# View the Pod and Service you created
5kubectl get pod,svc -n kube-system
6# Disable metrics-server
7minikube addons disable metrics-server

Cheatsheet

  • kubectl get - list resources
  • kubectl describe - show detailed information about a resource
  • kubectl logs - print the logs from a container in a pod
  • kubectl exec - execute a command on a container pod. Example: kubectl exec kubernetes-bootcamp-57978f5f5d-zpk6t -- env