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Kubernetes - Objects: Annotations

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• Kubernetes - Objects: Annotations
  • Annotation
    • Imperative Commands
    • Declarative Manifest
  • Lab: Annotation

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Annotation

• limitation of labels:

  • maximum length of a label value is only 63 characters
  • the value can’t contain whitespace at all.

• Annotation

  • a key–value pair of metadata attached to an object that is intended only for information storage and reference
  • not for identification, grouping, or selection.
  • up to 256 KB
  • can contain any character
  • must be a string
    • can contain plain text, YAML, JSON, or even a Base64-Encoded value.

• Common use cases:

  • attach the URL of the Git repository
  • the Git commit hash
  • the build timestamp
  • pod description
  • creator of the object
  • bool value to signal to the deployment tool

• vs label

  • Labels: selection & grouping
  • Annotations: configuration & behavior

• Whether trigger roll out?

  • only when the Pod template changed in Deployment
    • .spec.template.metadata.annotations triggers roll out
  • not when pod, svc, etc.

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Imperative Commands

CMD	DESC
kubectl annotate pod mypod key=value	Add an annotation
kubectl annotate pod mypod key=value key2=value2	Add multiple annotations
kubectl annotate pod mypod key=value --overwrite	Update existing annotation
kubectl annotate pod mypod key-	Delete an annotation
kubectl annotate pod mypod --list	List annotations on the object
kubectl annotate deploy myapp team=backend	Annotate a Deployment
kubectl annotate svc mysvc description="internal service"	Annotate a Service
kubectl annotate node node1 zone=us-east-1a	Annotate a Node
kubectl annotate ns dev owner=platform-team	Annotate a Namespace
kubectl annotate pod mypod key=value --record	Record annotation change in rollout history

• Create pod with annotation

kubectl run nginx-demo --image=nginx --annotations="owner=platform-team,env=dev,purpose=demo"

• View Annotations

CMD	DESC
kubectl get pod mypod -o yaml	View all annotations
kubectl describe pod mypod	Human readable annotation view
kubectl get pod mypod -o jsonpath='{.metadata.annotations}'	Print annotations only

• Real-World Examples

Purpose	Example
AWS ALB	alb.ingress.kubernetes.io/scheme=internet-facing
cert-manager	cert-manager.io/cluster-issuer=letsencrypt-prod
ArgoCD	argocd.argoproj.io/sync-wave=5
Helm	meta.helm.sh/release-name=myapp

---

Declarative Manifest

apiVersion: v1
kind: Pod
metadata:
  name: nginx-annotated
  labels:
    app: nginx
  annotations:
    # pod info
    description: "Demo nginx pod with annotations"
    owner: "platform-team"
    last-updated-by: "kubectl"
    purpose: "testing-annotation"
    # Auto Scrape
    prometheus.io/scrape: "true"
    prometheus.io/port: "80"
    prometheus.io/path: "/metrics"
spec:
  containers:
    - name: nginx
      image: nginx:latest
      ports:
        - containerPort: 80

---

Lab: Annotation

# create pod with annotation
kubectl run nginx --image=nginx --annotations="owner=platform-team,env=dev,purpose=demo"
# pod/nginx created

kubectl describe pod nginx
# Annotations:      owner: platform-team,env=dev,purpose=demo

# add annotation
kubectl annotate pod nginx created-by='creator' managed-by='terraform'
# pod/nginx annotated

# confirm
kubectl get pod nginx -o jsonpath='{.metadata.annotations}'
# '{"created-by":"'creator'","managed-by":"'terraform'","owner":"platform-team,env=dev,purpose=demo"}'

# update
kubectl annotate pod nginx managed-by='helm' --overwrite
# pod/nginx annotated

# confirm
kubectl get pod nginx -o jsonpath='{.metadata.annotations.managed-by}'
# ''helm''

# delete
kubectl annotate pod nginx managed-by- created-by-
# pod/nginx annotated

# confirm 
kubectl get pod nginx -o=jsonpath="{.metadata.annotations}"
# {"owner":"platform-team,env=dev,purpose=demo"}