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What is a label?

Learn to tag resources with labels.

What is a label?

A label is a key: value pair attached to objects. Kubernetes links objects to each other not by name but by label: a Service finds its pods and a Deployment its ReplicaSets by label. Labels are also used for filtering and organization:

metadata:
  name: web-7c5b9f6d8-abcde
  labels:
    app: web
    katman: on
    ortam: prod
    app.kubernetes.io/version: "1.4.2"

The recommended common labels are app.kubernetes.io/name, /instance, /version, /component and /part-of.

Label rules

A label key consists of an optional prefix (domain.com/) and a name of at most 63 characters; the value is also at most 63 characters and may contain letters, digits, -, _ and .. Spaces and Turkish characters can't be used. Numbers like version numbers are quoted in YAML:

labels:
  app: web            # valid
  surum: "2"          # a number: quote it
  takim: odeme-ekibi  # valid
  aciklama: ana sayfa # INVALID: space

Practice A labelled pod

Write a pod YAML: name web; labels app: web, katman: on, ortam: prod; container named nginx, image nginx:1.27.

Starter code

terminal
# buraya yaz

Sample solution

terminal
apiVersion: v1
kind: Pod
metadata:
  name: web
  labels:
    app: web
    katman: on
    ortam: prod
spec:
  containers:
    - name: nginx
      image: nginx:1.27

Expected output

pod/web created

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What is the difference between a label and an annotation?

  • Labels can't be changed
  • Labels are used in selectors; annotations are extra info that can't be selected Correct answer
  • They are the same
  • Annotations exist only on pods

Explanation: Annotations are for data like long text, URLs and tool settings.

2 Define the object's labels.

Question 
metadata:
  name: web
  ____:
    app: web
Answer 
metadata:
  name: web
  labels:
    app: web

Explanation: labels is under metadata.

3 Match.

Term Meaning
label Selectable key-value
annotation Non-selectable extra info
app.kubernetes.io/name Recommended common label
63 karakter Name/value limit

All lessons in Intermediate

1 What is Kubernetes?

  1. What is Kubernetes?
  2. Why Kubernetes?
  3. Cluster architecture
  4. Control plane
  5. Worker node
  6. Summary - What is Kubernetes

2 Minikube

  1. What is Minikube?
  2. Installing Minikube
  3. minikube start
  4. minikube status
  5. minikube dashboard
  6. Summary - Minikube

3 kubectl basics

  1. What is kubectl?
  2. kubectl get
  3. kubectl describe
  4. kubectl apply
  5. kubectl delete
  6. Summary - kubectl

4 Pod

  1. What is a Pod?
  2. Pod YAML
  3. Creating a Pod
  4. Pod status
  5. Multi-container Pod
  6. Summary - Pod

5 Deployment

  1. What is a Deployment?
  2. Deployment YAML
  3. Replica count
  4. Rolling update
  5. Rollback
  6. Summary - Deployment

6 ReplicaSet

  1. What is a ReplicaSet?
  2. ReplicaSet YAML
  3. ReplicaSet selector
  4. Scaling
  5. Self-healing
  6. Summary - ReplicaSet

7 Service

  1. What is a Service?
  2. ClusterIP
  3. NodePort
  4. LoadBalancer
  5. Service selector
  6. Summary - Service

8 ConfigMap

  1. What is a ConfigMap?
  2. ConfigMap YAML
  3. Environment variable
  4. Mounting as a volume
  5. kubectl create configmap
  6. Summary - ConfigMap

9 Secret

  1. What is a Secret?
  2. Secret types
  3. Secret YAML
  4. Mounting a Secret
  5. kubectl create secret
  6. Summary - Secret

10 Namespace

  1. What is a Namespace?
  2. kubectl get namespaces
  3. Creating a Namespace
  4. The -n flag
  5. Default Namespace
  6. Summary - Namespace

11 Labels and selectors

  1. What is a label?
  2. Adding labels
  3. Label selector
  4. kubectl get -l
  5. Equality and set selectors
  6. Summary - Labels

12 Project: Multi-tier app

  1. Project design
  2. Database Deployment
  3. Web Deployment
  4. ConfigMap and Secret
  5. Putting it together - multi-tier

13 Troubleshooting

  1. kubectl logs
  2. kubectl exec
  3. kubectl describe pod
  4. CrashLoopBackOff
  5. Pending Pod
  6. Summary - Troubleshooting

14 Intermediate final

  1. Challenge - Pod YAML
  2. Challenge - Deployment
  3. Challenge - Service
  4. Challenge - ConfigMap
  5. Challenge - Intermediate project