Kubernetes - Namespace

Default namespace created by Kubernetes 

• kube-system
• kube-public
• default

How it is helpful ?

• These different namespace 
• can be used by same cluster for DEV and PROD environment.
• they will have isolated resources between them so that DEV will have their own resource and PROD will have their own resource.
• they will have their own policies that define who can do what
• Each namespace has a max limit of resources and are not allowed to use more than its allowed limit. 
• We can define policy such that for example, while working in DEV environment, we can't modify a resource of PRODUCTION.

Example usage of custom namespace. 

• Dev
• Test
• Prod

How to name resources of a namespace?

• Same namespace 
• Resources in same namespace ca access via db-service
• Different namespace
• Resources in other namespace can access resources in other namespace via ( say DEV resources via - db-service.dev.svc.cluster.local 

Name details

db-service.dev.svc.cluster.local 

• db-service - Name of the service
• dev - namespace
• svc - service
• cluster.local - domain.

How to create Namspace Or Pod Inside Namespace

• Create in default namespace
• kubectl create -f pod-definition.yml -f
• Create a particular namespace
• kubectl create -f pod-definition --namespace dev
• kubectl create -f pod-definition -n dev
• Create a Namespace
• kubectl create -f namespace-dev.yaml
• kubectl create namespace dev
• Sample Yaml file for Namespace
• apiVersion: v1
• kind: Namespace
• metadata:
• name: dev
• Create POD under a namespace through Yaml file
• apiVersion: v1
• kind: Pod
• metadata
• name: myapp-pod
• namespace: dev
• label
• app: myapp
• type: front-end
• spec
• container:
• name: nginx-container
• image: nbinx
• Accessing Namespace
• Scenario -1 : Access default namespace
• kubectl get pods 
• kubectl get pods --namespace dev
• kubectl get pods --namespace prod

• Change the default namespace to namespace = dev
• kubectl config set-context  $(kubectl config current-context) --namespace dev
• kubectl get pods  <<<< This will show Pods from namespace = DEV.
• kubectl get pods --namespace default << To access default namespace
• kubectl get pods --namespace prod << To access PROD namespace
• Resource Quota
• Resources can be limited in a namespace.
• apiVersion: v1
• kind: ResourceQuota
• metadata:
• name: compute-quota
• namespace: dev
• spec:
• hard:
• pods: "10",
• requests-cpu: "4"
• requests-memory: 5Gi
• limts-cpu: "10"
• limits-memory: 10Gi

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Kubernetes- Deployment

- Defines how to deploy application in production environment.

Scenarios

• Old instance running - Multiple Pod having applications are running in production environment.
• New version of application is available - need to upgrade seamlessly- without any downtime.
• Rolling update
• For this we don't want to upgrade all of them at once as this may impact accessibility. 
• One by one upgrade - And we might want to upgrade one after other.
• In case of failure - we should be able to rollback the upgrade.
• Multiple change to environment - 
• Ex - Scaling the environment, Modifying resource allocation etc.
• And this change should be done for all PODS together and then activated for all Pods as the same time.

Kubernetes Deployment

• Comes at the top of the hierarchy.
• Comes at top of Pod and Replica Set.

• Available with
• Rolling update
• Undo changes
• Pause changes
• Resume changes

How to create deployment

Yaml file 

• same as ReplicaSet except for change in KIND.

apiVersion: apps/v1   

kind: Deployment      << Only change done for Deployment

metadata:

  name: myapp-replicaset

  labels:

    app: myapp

    type: front-end

spec:

  template:   <<< Here need to provide template for POD. We just to insert metadata + spec section of POD.

    metadata:

      name: myapp-pod

      labels:

        app: myapp

        type: front-end

    

    spec:   

      containers: 

        name: nginx-container

        image: nginx

  replicas: 3   <<< This is sibling of template

  selector:        

    matchLabels:

      type: front-end

Commands

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