Kubernetes - Lab - Label and selectors

 

Labels and selectors

go down for lab

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Kubernetes objects 

Imperative LAB tasks

Here, is a POD definition file.

# cat pod-definition-file.yaml

apiVersion: v1

kind: Pod

metadata:

  name: myapp-pod

  labels:

    app: myapp

    type: front-end-service

sepc: 

    nodeName: 

    containers:

    - name: nginx-container

      image: nginx:1.19

      ports:

        - containerPort: 8080

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Group them based on need

label - 

class kind and color

we created different objects - pod, services, replica sets, deployment 

group and select

Labels

app: app1

function: frond-end

app: app2

function: web-services

app: app3

function: Images-proc

app: app5

function: DB

How do you specify lables in kubernetes

In pod definition file, under metadata, there is a section called labels

# cat pod-definition-file.yaml

apiVersion: v1

kind: Pod

metadata:

  name: myapp-pod

  labels:

    app: myapp1

    function: Front-end

    type: front-end-service

sepc: 

    containers:

    - name: nginx-container

      image: nginx:1.19

      ports:

        - containerPort: 8080

# kc apply -f pod.yaml

# kc get pods --selector app=app1

Lets create a replicaSet with three replicas

# cat pod-definition-file.yaml

apiVersion: v1

kind: Replicaset

metadata:

  name: myapp-pod

  labels:

    app: myApp1 # this is the label for replicaset

    function: Front-end

  annotations:

      buildversion: 1.34

sepc: 

  replicas: 3

  selector:

    matchLabels:

      app: myApp1

  template:

    metadata:

      labels:

        app: myApp1 # label defined at template section is for POD

        function: Front-end

    spec:

      containers:

      - name: nginx-container

        image: nginx:1.19

Lab - Label and selectors

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1. We have deployed a number of PODs. They are labelled with 'tier', 'env' and 'bu'. How many PODs exist in the 'dev' environment?

Use selectors to filter the output

-> Run the command 'kubectl get pods --selector env=dev'

# kc get pods

# kc get pors --show-labels

# kc get pods -l env=dev --no-headers | wc -l 

or

# kc get pods --selector env=dev 

2. How many PODs are in the 'finance' business unit ('bu')?

-> Run the command 'kubectl get pods --selector bu=finance'

# kc get pods --selector bu=finance 

or

# kc get pods -l bu=finance --no-headers | wc -l

3. How many objects are in the 'prod' environment including PODs, ReplicaSets and any other objects?

-> Run the command 'kubectl get all --selector env=prod'

# kc get pods --selector env=prod

or

kc get pods -l env=prod --no-headers

we need all object, not only pod, so run all

# kc get all -l env=prod --no-headers | wc -l

count all output, here 7

5. Identify the POD which is part of the prod environment, the finance BU and of frontend tier?

-> Run the command 'kubectl get all --selector env=prod,bu=finance,tier=frontend'

# kc get pods --selector env=prod,bu=finance,tier=frontend

# kc get all --selector env=prod,bu=finance,tier=frontend

or

# kc get pods -l env=prod,bu=finance,tier=frontned

6. A ReplicaSet definition file is given 'replicaset-definition-1.yaml'. Try to create the replicaset. There is an issue with the file. Try to fix it.

    ReplicaSet: replicaset-1

    Replicas: 2 

-> Set the labels on the pod definition template to frontend

here, lets go ahead and create replicaset

# kc create -f replica-definition-1.yaml

error with selector does not match template 'labels'

edit the file,

# cat replica-definition-1.yaml

apiVersion: v1

kind: ReplicaSet

metadata:

  name: replicaset-1

 

sepc: 

    replicas: 2

    selector:

      matchLabels:

        tier: frontend

    template:

      metadata:

        labels:

          tier: frontend

      spec:

        containers:

        - name: nginx

          image: nginx

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