Use k8s api to get service endpoint information

Order

This article mainly studies how to use k8s api to obtain service endpoint information

mac m2 install k8s

Install multipass

Visit https://multipass.run/install, download and install

Create instance

multipass launch --name primary --cpus 2 --disk 20G --memory 4G

Install microk8s

sudo snap install microk8s --classic
sudo usermod -a -G microk8s $USER
sudo chown -f -R $USER ~/.kube
microk8s status --wait-ready

Configure aliases(~/.bash_aliases)

alias kubectl='microk8s kubectl'

Check if it is ready

kubectl get node

If it is not ready, there is a high probability that the pause image cannot be pulled. Use pullk8s to correct it and make a slight change

#!/bin/bash

check(){
  if [ "$1"x == "--microk8s"x ]
  then
    logs=`microk8s kubectl get pod --all-namespaces|tail -n + 2|grep -v Running|while read line
    do
     declare -a arr=( $line )
     microk8s kubectl describe pod ${arr[1]} --namespace=${arr[0]}
    done|grep -i "image"|sed -nr 's/.*(failed to pull|Back-off pulling) image "([^"] + )". */\2/p'|uniq`
    echo ${logs}
  the fi
}

pull(){
  image=$1
  imageName=${image/#registry\.k8s\.io\//}
  if [ "$image"x == "$imageName"x ]
  then
    imageName=${image/#gcr\.io\/google_containers\//}
  the fi
  echo Pull $imageName ...
  if [ "$image"x == "$imageName"x ]
  then
    echo Pull $imageName ...
    docker pull $image
    exit 0
  the fi
  hubimage=${imageName//\//\-}

  if [ -n "$hubimage" ]
  then
    echo Pull $imageName ...
    docker pull opsdockerimage/$hubimage
    docker tag opsdockerimage/$hubimage $1
    docker rmi opsdockerimage/$hubimage
    if [ "$2"x == "--microk8s"x ]
    then
      saveImage=${1#:}
      docker save $saveImage > ~/.docker_image.tmp.tar
      microk8s ctr image import ~/.docker_image.tmp.tar
      rm ~/.docker_image.tmp.tar
    the fi
  the fi
}

then execute

pullk8s check --microk8s
pullk8s pull registry.k8s.io/pause:3.7 --microk8s
microk8s stop
microk8s start

Example

Create nginx

kubectl create deployment nginx --image=nginx
kubectl expose deployment nginx --port=8000 --target-port=80 --name=ngsvc
kubectl scale deployment nginx --replicas=3

View with kubectl

kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.152.183.1 <none> 443/TCP 87m
ngsvc ClusterIP 10.152.183.50 <none> 8000/TCP 3m44s

kubectl get pods
NAME READY STATUS RESTARTS AGE
nginx-77b4fdf86c-xbd6s 1/1 Running 0 18m
nginx-77b4fdf86c-g9gt5 1/1 Running 0 2m35s
nginx-77b4fdf86c-xq76f 1/1 Running 0 2m35s

kubectl get endpoints
NAME ENDPOINTS AGE
kubernetes 192.168.64.2:16443 85m
ngsvc 10.1.226.133:80,10.1.226.134:80,10.1.226.135:80 64s

Use api view in pod

kubectl get pods
kubectl exec -it nginx-77b4fdf86c-xbd6s sh


# Point to the hostname of the internal API server
APISERVER=https://kubernetes.default.svc

# Path to the service account token
SERVICEACCOUNT=/var/run/secrets/kubernetes.io/serviceaccount

# Read the Pod's namespace
NAMESPACE=$(cat ${SERVICEACCOUNT}/namespace)

# Read the holder token of the service account
TOKEN=$(cat ${SERVICEACCOUNT}/token)

# reference the internal certificate authority (CA)
CACERT=${SERVICEACCOUNT}/ca.crt

# Use the token to access the API
curl --cacert ${CACERT} --header "Authorization: Bearer ${TOKEN}" -X GET ${APISERVER}/api/v1/namespaces/default/endpoints/ngsvc

returns as follows:

{
  "kind": "Endpoints",
  "apiVersion": "v1",
  "metadata": {
    "name": "ngsvc",
    "namespace": "default",
    "uid": "bccd1acd-a8e2-419f-925e-8ae324bf2e8b",
    "resourceVersion": "5344",
    "creationTimestamp": "2023-07-22T05:57:24Z",
    "labels": {
      "app": "nginx"
    },
    "annotations": {
      "endpoints.kubernetes.io/last-change-trigger-time": "2023-07-22T05:58:26Z"
    },
    "managedFields": [
      {
        "manager": "kubelite",
        "operation": "Update",
        "apiVersion": "v1",
        "time": "2023-07-22T05:58:26Z",
        "fieldsType": "FieldsV1",
        "fieldsV1": {
          "f:metadata": {
            "f:annotations": {
              ".": {},
              "f:endpoints.kubernetes.io/last-change-trigger-time": {}
            },
            "f:labels": {
              ".": {},
              "f:app": {}
            }
          },
          "f:subsets": {}
        }
      }
    ]
  },
  "subsets": [
    {
      "addresses": [
        {
          "ip": "10.1.226.133",
          "nodeName": "primary",
          "targetRef": {
            "kind": "Pod",
            "namespace": "default",
            "name": "nginx-77b4fdf86c-xbd6s",
            "uid": "ebc83b51-a438-40a8-b543-17a14d98a267"
          }
        },
        {
          "ip": "10.1.226.134",
          "nodeName": "primary",
          "targetRef": {
            "kind": "Pod",
            "namespace": "default",
            "name": "nginx-77b4fdf86c-g9gt5",
            "uid": "956cda5b-1724-49f3-9bc6-96c523c3c946"
          }
        },
        {
          "ip": "10.1.226.135",
          "nodeName": "primary",
          "targetRef": {
            "kind": "Pod",
            "namespace": "default",
            "name": "nginx-77b4fdf86c-xq76f",
            "uid": "731f4544-2ccc-46c0-aeb6-610bd2a4fdf8"
          }
        }
      ],
      "ports": [
        {
          "port": 80,
          "protocol": "TCP"
        }
      ]
    }
  ]
}

Access outside the container

Get api address

kubectl get endpoints kubernetes
NAME ENDPOINTS AGE
kubernetes 192.168.64.2:16443 108m

View token

/var/snap/microk8s/current/credentials/known_tokens.csv

Get admin token

Visit

curl -k --header "Authorization: Bearer ${token}" -X GET https://192.168.64.2:16443/api/v1/namespaces/default/endpoints/ngsvc

Replace the token obtained in the previous step with ${token}

Summary

The api of k8s provides an interface for obtaining endpoints, and the list of corresponding pods can be obtained according to the service

doc

• Use multipass to build a linux development environment on mac
• github.com/OpsDocker/pullk8s
• Access the Kubernetes API from within a pod