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Lab Kubernetes API

Objective

The focus of this lab is to become familar with the kube-api. Through this lab you should have an understanding of the kube-api, how it can be accessed and how the API is formed.

  1. Start cluster

kind create cluster

kind create cluster
Creating cluster "kind" ...
 ✓ Ensuring node image (kindest/node:v1.17.0) 🖼
 ✓ Preparing nodes 📦  
 ✓ Writing configuration 📜 
⠊⠁ Starting control-plane 🕹️ on
 ✓ Starting control-plane 🕹️ 
 ✓ Installing CNI 🔌 
 ✓ Installing StorageClass 💾 
Set kubectl context to "kind-kind"
You can now use your cluster with:

kubectl cluster-info --context kind-kind

Have a nice day! 👋
  1. Access the API via kubectl

Try the following: k get --raw /

Get namespaces k get --raw /api/v1/namespaces k get --raw /api/v1/namespaces/default

k get --raw /api/v1/namespaces/default/ 
{"kind":"Namespace","apiVersion":"v1","metadata":{"name":"default","selfLink":"/api/v1/namespaces/default","uid":"288cb0cf-4257-4288-9863-d313bc502972","resourceVersion":"146","creationTimestamp":"2020-02-02T03:15:52Z"},"spec":{"finalizers":["kubernetes"]},"status":{"phase":"Active"}}

tip: jq or python json.tool can make this easier to read. k get --raw /api/v1/namespaces/default | jq . or k get --raw /api/v1/namespaces/default | python -m json.tool

  1. Time for a proxy

k proxy

 k proxy
Starting to serve on 127.0.0.1:8001

curl localhost:8001 curl localhost:8001/api/v1/namespaces/default

note: exit proxy with ctrl+c

  1. api-resouces

Lets get a list of resources from kubectl k api-resources

Which resources are namespaced? and which are cluster scoped?

For cluster scoped: k api-resources --namespaced=false

What is the shortname for PodSecurityPolicy?

  1. Explaining Resources

Explain is a great way to understand the defined structure of a resource or kind. This is accomplish through k explain <kind>

k explain ns

Almost all resources at this high level report roughly the same apiVersion, kind, metadata, spec, status information. In order to get the full structure of this kind use the --recursive flag.

k explain ns --recursive

Notice the status field phase. Let's display that as an output.

k get ns -o custom-columns=NAME:.metadata.name,PHASE:.status.phase

Example output:

NAME                 PHASE
default              Active
kube-node-lease      Active
kube-public          Active
kube-system          Active
local-path-storage   Active

Explain is incredibly useful in understanding the structure of types deployed in kubernetes.

Summary

The Kubernetes API server is the gateway into kubernetes and is accessed via HTTP. All interactions with Kubernetes is through it. All controllers / operators work through API for read, update and control.

todo: use v=9 tracing