These are used to organize our application.
Lables
Labels are key:value pairs. These can be attached to objects like pods, services, deployments. Labels are mainly used to organize Kubernetes objects.
Why labels?
a. Users can easily identify the objects.
b. Used to organize clusters
Can I change the labels at runtime?
Labels can be added at deployment time and can be changed at any time.
Example
environment:prod
release:beta
service:front-end
For example, you have hundreds of microservices running in Kubernetes Environment. By providing labels like appType, environment you can easily organize them. Below image depicts the same.
From the above image, you can easily query for all the pods that of type ‘weservice’ and running in prod environment.
employeeServiceDeployment.yml
apiVersion: apps/v1
kind: Deployment
metadata:
name: employee-service-deployment
labels:
app: employee-service-deployment
author: krishna
serviceType: webservice
........
........
In the above example, I added labels app, author, serviceType to the Deployment.
Selectors
Label selectors are used to identify a group of objects.
Types of selectors
a. Equality Based Selector: =, !=
b. Set Based Selector: IN, NONIN, EXISTS
Label Selectors are used with kubectl command.
Namespaces
Allow multiple virtual clusters backed by the same physical cluster. When you launch Kubernetes, a ‘default’ namespace is created. Objects are placed in ‘default’ namespace by default.
Annotations
Annotations provide detailed metadata in an object (For example, who created this pod etc.,). Annotations are used by tools.
Syntax to create annotation
kubectl annotate pod {podName} annotation1=value1
Can I use annotations in queries?
No, annotation is used to provide additional information.
Let’s create a deployment and add labels and annotations to it.
Step 1: Create a deployment.
employeeServiceDeployment.yml
apiVersion: apps/v1
kind: Deployment
metadata:
name: employee-service-deployment
labels:
app: employee-service-deployment
author: krishna
serviceType: webservice
spec:
template:
metadata:
name: employee-service
labels:
app: employee-service
author: krishna
serviceType: webservice
spec:
containers:
- name: employee-service-container
image: jboss/wildfly
replicas: 5
selector:
matchLabels:
app: employee-service
As you see the definition file, I added three labels to the deployment.
labels:
app: employee-service-deployment
author: krishna
serviceType: webservice
Create deployment by executing the below command.
$kubectl create -f employeeServiceDeployment.yml
deployment.apps/employee-service-deployment created
You can get all the deployments by executing the below command.
$kubectl get deployments
NAME READY UP-TO-DATE AVAILABLE AGE
employee-service-deployment 5/5 5 5 29s
Step 2: Let's add a label to the deployment ‘employee-service-deployment’.
kubectl label deployment employee-service-deployment env=prod version=1.24
Above statement adds two labels env, version to the deployment ‘employee-service-deployment’.
$kubectl label deployment employee-service-deployment env=prod version=1.24
deployment.apps/employee-service-deployment labelled
Step 3: Let’s see the labels by executing the below command.
kubectl get deployments --show-labels
$kubectl get deployments --show-labels
NAME READY UP-TO-DATE AVAILABLE AGE LABELS
employee-service-deployment 5/5 5 5 3m15s app=employee-service-deployment,author=krishna,env=prod,serviceType=webservice,version=1.24
Step 4: Let's create other deployments to understand the usage of selectors.
notificationServiceDeployment.yml
apiVersion: apps/v1
kind: Deployment
metadata:
name: notification-service-deployment
labels:
app: notification-service-deployment
author: krishna
serviceType: webservice
spec:
template:
metadata:
name: notification-service
labels:
app: notification-service
author: krishna
serviceType: webservice
spec:
containers:
- name: notification-service-container
image: jboss/wildfly
replicas: 10
selector:
matchLabels:
app: notification-service
Create the deployment by executing the below command.
$kubectl create -f notificationServiceDeployment.yml
deployment.apps/notification-service-deployment created
Let’s see the labels associated with all the deployments.
$kubectl get deployments --show-labels
NAME READY UP-TO-DATE AVAILABLE AGE LABELS
employee-service-deployment 5/5 5 5 6m42s app=employee-service-deployment,author=krishna,env=prod,serviceType=webservice,version=1.24
notification-service-deployment 5/10 10 5 27s app=notification-service-deployment,author=krishna,serviceType=webservice
Step 5: Query the deployments using selectors.
kubectl get deployments --selector app=employee-service-deployment
kubectl get deployments --selector version=1.24
$kubectl get deployments --selector app=employee-service-deployment
NAME READY UP-TO-DATE AVAILABLE AGE
employee-service-deployment 5/5 5 5 8m51s
$
$
$kubectl get deployments --selector version=1.24
NAME READY UP-TO-DATE AVAILABLE AGE
employee-service-deployment 5/5 5 5 9m13s
Step 6: You can even get the selector used by Kubernetes for the deployments by executing ‘kubectl describe’ command.
kubectl describe deployment employee-service-deployment
$kubectl describe deployment employee-service-deployment
Name: employee-service-deployment
Namespace: default
CreationTimestamp: Sun, 07 Jun 2020 15:12:19 +0530
Labels: app=employee-service-deployment
author=krishna
env=prod
serviceType=webservice
version=1.24
Annotations: deployment.kubernetes.io/revision: 1
Selector: app=employee-service
Replicas: 5 desired | 5 updated | 5 total | 5 available | 0 unavailable
StrategyType: RollingUpdate
MinReadySeconds: 0
RollingUpdateStrategy: 25% max unavailable, 25% max surge
Pod Template:
Labels: app=employee-service
author=krishna
serviceType=webservice
Containers:
employee-service-container:
Image: jboss/wildfly
Port: <none>
Host Port: <none>
Environment: <none>
Mounts: <none>
Volumes: <none>
Conditions:
Type Status Reason
---- ------ ------
Available True MinimumReplicasAvailable
Progressing True NewReplicaSetAvailable
OldReplicaSets: <none>
NewReplicaSet: employee-service-deployment-dff6c9cdf (5/5 replicas created)
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal ScalingReplicaSet 14m deployment-controller Scaled up replica set employee-service-deployment-dff6c9cdf to 5
As you see the output, you will find the below statement.
Selector: app=employee-service
How to delete a label?
$kubectl get deployments --show-labels
NAME READY UP-TO-DATE AVAILABLE AGE LABELS
notification-service-deployment 10/10 10 10 26s app=notification-service-deployment,author=krishna,serviceType=webservice
Using – operator, we can delete the label.
For example, below statement delete the label app from the deployment.
kubectl label deployments notification-service-deployment app-
Let's delete the label for pods.
$kubectl get pods --show-labels
NAME READY STATUS RESTARTS AGE LABELS
notification-service-deployment-7dc84f6d4-5wtsg 1/1 Running 0 2m33s app=notification-service,author=krishna,pod-template-hash=7dc84f6d4,serviceType=webservice
notification-service-deployment-7dc84f6d4-7cc8p 1/1 Running 0 2m33s app=notification-service,author=krishna,pod-template-hash=7dc84f6d4,serviceType=webservice
notification-service-deployment-7dc84f6d4-92ftm 1/1 Running 0 2m33s app=notification-service,author=krishna,pod-template-hash=7dc84f6d4,serviceType=webservice
notification-service-deployment-7dc84f6d4-9prw6 1/1 Running 0 2m33s app=notification-service,author=krishna,pod-template-hash=7dc84f6d4,serviceType=webservice
notification-service-deployment-7dc84f6d4-crknr 1/1 Running 0 2m33s app=notification-service,author=krishna,pod-template-hash=7dc84f6d4,serviceType=webservice
notification-service-deployment-7dc84f6d4-ct7bq 1/1 Running 0 2m33s app=notification-service,author=krishna,pod-template-hash=7dc84f6d4,serviceType=webservice
notification-service-deployment-7dc84f6d4-g8hc6 1/1 Running 0 2m33s app=notification-service,author=krishna,pod-template-hash=7dc84f6d4,serviceType=webservice
notification-service-deployment-7dc84f6d4-mnlb2 1/1 Running 0 2m33s app=notification-service,author=krishna,pod-template-hash=7dc84f6d4,serviceType=webservice
notification-service-deployment-7dc84f6d4-sgrm4 1/1 Running 0 2m33s app=notification-service,author=krishna,pod-template-hash=7dc84f6d4,serviceType=webservice
notification-service-deployment-7dc84f6d4-tlsb4 1/1 Running 0 2m33s app=notification-service,author=krishna,pod-template-hash=7dc84f6d4,serviceType=webservice
Below statement delete the label author from the pods.
kubectl label pods notification-service-deployment-7dc84f6d4-5wtsg author-
$kubectl label pods notification-service-deployment-7dc84f6d4-5wtsg author-
pod/notification-service-deployment-7dc84f6d4-5wtsg labeled
$
$kubectl get pods notification-service-deployment-7dc84f6d4-5wtsg --show-labels
NAME READY STATUS RESTARTS AGE LABELS
notification-service-deployment-7dc84f6d4-5wtsg 1/1 Running 0 4m36s app=notification-service,pod-template-hash=7dc84f6d4,serviceType=webservice
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