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Kubernetes: 4. Namespaces

  • All the default pods that are required for networking, DNS etc are kept in kube-system namespace
  • The resource that are to be made available to the public are kept in kube-public namespace
  • All the user created resources can be kept in the default namespace or a custom namespace

Custom Namespaces
  • Can have their own policies, defining what can be done in the namespace
  • Resource quotas [CPU, Memory] can be enforced in the namespace
  • Each resource within the namespace can be reached directly by its service name
  • A resource in a namespace can reach to the resource in another namespace by appending the namespace name and further appending ".svc.cluster.local"
  • So a db-service pod in a dev namespace can reached as db-service.dev.svc.cluster.local
  • Note that we are referring to service-name here and NOT the pod-name
  • This is because when a service is created a DNS entry is automatically created in the above format
    • cluster.local is the domain name
    • svc is the sub-domain for service
    • dev is the namespace
    • db-service is the service name
  • To set the quota limits in a namespace, create the resource definition file for the namespace and set the limits in it

ResourceQuota
  • If a resource quota is applied to a namespace then all pod containers have to declare the requests and limits for CPU and Memory
  • Sum of all the CPU/Memory requests/limits in the pod cannot be more than what is declared in ResourceQuota for namespace
  • Requests are what containers gets for sure
  • Limits are the threshold values beyond which a container cannot go
  • Limit is always  set greater than requests otherwise kubernetes throws an error

namespace-definition.yaml
apiVersion: v1
kind: Namespace
metadata:
    name: dev

compute-resource-quota-definition.yaml
apiVersion: v1
kind: ResourceQuota
metadata:
    name: compute-quota
    namespace: dev

spec:
    hard:
        pods: "10"
        requests.cpu: "4"
        requests.memory: "5Gi"
        limits.cpu: "10"
        limits.memory: "10Gi"

pod-definition-with-namespace.yaml
apiVersion: v1
kind: Pod
metadata:
    name: myapp-pod
    namespace: dev
    labels:
        app: myapp
        location: IN

spec:
    containers:
    - name: nginx-container
    image: nginx
    - name: backed-db
    image: redis

pod-definition.yaml
apiVersion: v1
kind: Pod
metadata:
    name: myapp-pod
    labels:
        app: myapp
        location: IN

spec:
    containers:
    - name: nginx-container
    image: nginx
    - name: backed-db
    image: redis

kubectl get pods                         
-> Get pods from default namespace

kubectl get pods --namespace kube-system 
-> Get pods from kube-system namespace

kubectl create -f pod-definition.yaml    
-> Create pod from definition file in default namespace

kubectl create -f pod-definition.yaml --namespace=dev 
-> Create pod from definition file in dev namespace, alternatively provide the namespace in metadata section

kubectl create -f namespace-definition.yaml 
-> Create[kubernetes resource] a namespace from definition file

kubectl create namespace dev             
-> Create a namespace from CLI

kubectl config set-context $(kubectl config current-context) --namespace=dev 
-> Set the dev namespace as the default namespace in the current context

kubectl get pods --all-namespaces        
-> Get pods from all the namespaces

kubectl create -f compute-resource-quota-definition.yaml 
-> Create[kubernetes resource] namespace and define the quotas in the namespace

kubectl get ns                           
-> Get the namespaces

kubectl get namespace                    
-> Get the namespaces



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