4. kubectl

The kubectl command-line utility is used to interact with the kubernetes API

Namespaces and (client) Contexts

kubectl config set-context my-context --namespace=mystuff

creates a new context

kubectl config use-context my-context

API Objects

are a RESTful Resource like https://my-k8s.com/api/v1/namespaces/default/pods/my-pod

get

wide / json / yaml

kubectl get pods my-pod -o jsonpath --template={.status.podIP}

describe

kubectl describe pods kuard

apply / delete

are done via yaml or json file -f obj.yaml

Debugging

logging

kubectl logs <pod-name> optionally following -f

execution

kubectl exec kuard date

kubectl exec -it kuard ash

copy

kubectl cp <pod-name>:/path/to/remote/file /path/to/local/file

port forwarding

kubectl port-forward kuard 8080:8080

Help

kubectl help

or

kubectl help <command-name>

5. Services

Create a Deployment:

kubectl run alpaca-prod --image=gcr.io/kuar-demo/kuard-amd64:1 --replicas=3 --port=8080 --labels="ver=1,app=alpaca,env=prod"

Create a Service with ClusterIP from the deployment:

kubectl expose deployment alpaca-prod optionally --type= NodePort or LoadBalancer

This ClusterIP can be resolved via DNS :

;; opcode: QUERY, status: NOERROR, id: 30123
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;alpaca-prod.default.svc.cluster.local.	IN	 A

;; ANSWER SECTION:
alpaca-prod.default.svc.cluster.local.	30	IN	A	10.100.196.205

11. ConfigMaps and Secrets

ConfigMap

kubectl create configmap my-config --from-file=my-config.txt --from-literal=extra-param=extra-value --from-literal=another-param=another-value

Secret

kubectl create secret generic kuard-tls --from-file=kuard.crt --from-file=kuard.key

Also useful imagePullSecrets

Also useful –dry-run -o yaml

kubectl create secret generic kuard-tls --from-file=kuard.crt --from-file=kuard.key --dry-run -o yaml | kubectl replace -f -

12. Deployments

create:

kubectl run nginx --image=nginx:1.7.12i

Relationship to the ReplicaSet is defined by label

kubectl get replicasets --selector=run=nginx

Exporting the yaml

kubectl get deployment nginx --export -o yaml > nginx-deployment.yaml

Updating a Container Image

Updating Image

      containers:
      - image: nginx:1.9.10
        imagePullPolicy: IfNotPresent

Putting an Annotation for Change Cause

  template:
    metadata:
      annotations:
        kubernetes.io/change-cause: "Update nginx to 1.9.10"

kubectl rollout status deployment nginx

kubectl rollout history deployment nginx

kubectl rollout pause deployment nginx

kubectl rollout resume deployment nginx

Undo Rollout

kubectl rollout undo deployment nginx --to-revision=3

13. Integrating Storage

External Database (IP)

A Service can have the type ExternalName.

kind: Service
apiVersion: v1
metadata:
  name: external-database
spec:
  type: ExternalName
  externalName: database.company.com

Or one can configure Endpoints manually for an IP Address.

kind: Service
apiVersion: v1
metadata:
  name: external-ip-database

kind: Endpoints
apiVersion: v1
metadata:
  name: external-ip-database
subsets:
  - addresses:
    - ip: 192.168.0.1
    ports:
    - port: 3306

MySQL Singleton

For example via EBS with PersistentVolume and PersistentVolumeClaim