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What is a Namespace?

A Namespace is used to isolate resources within a single cluster. Each namespace can have its own policies, permissions (RBAC), and resource controls. In other words, it is used to isolate users’ accessibility. By default, Kubernetes creates 4 namespaces:
NamespaceDescription
defaultThe namespace you can deploy to without creating a new namespace when starting a new cluster.
kube-systemNamespace for objects created by the Kubernetes system (kube-dns, kube-proxy, kubernetes-dashboard, etc.).
kube-publicContains resources readable publicly by all users without authentication. Mainly reserved for cluster usage.
kube-node-leaseHolds Lease objects associated with each node. Node leases allow kubelet to send heartbeats so the control plane can detect node failure.

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Commands

kubectl get <resource> -n <namespace-name>
kubectl get <resource> --namespace=<namespace-name>
kubectl get <resource> --all-namespaces

# Example
kubectl get pods -n dev

# Create a namespace
kubectl create namespace dev

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Switch Namespace Permanently

To switch to another namespace permanently (so you don’t have to specify it each time): 
kubectl config set-context $(kubectl config current-context) --namespace=<namespace-name>

kubectl get <resource>  # defaults to your namespace
A context is a set of access parameters that define a cluster, namespace, and user in Kubernetes. Contexts are stored in the kubeconfig YAML file and are used to manage multiple clusters or environments from the same system.

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Namespace YAML

apiVersion: v1
kind: Namespace
metadata:
  name: dev

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Using a Namespace in Resource YAML

apiVersion: v1
kind: Pod
metadata:
  name: sample-nginx-pod
  namespace: dev
spec:
  containers:
    - name: nginx
      image: nginx

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Connecting to Services in Other Namespaces

To connect to a service in another namespace, reference its DNS entry (automatically added when the service is created): 
Format:  <service-name>.<namespace>.svc.cluster.local
Example: db-svc.prod.svc.cluster.local
  • cluster.local is the default domain name of the Kubernetes cluster.

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Resource Quota for a Namespace

You can limit the total resources used within a namespace.
  • Scope: Applies to an entire namespace
  • Purpose: Enforces overall resource usage limits for all pods
  • Usage: Ensures total consumption (CPU, memory, number of pods) does not exceed specified limits
resource-quota.yaml
apiVersion: v1
kind: ResourceQuota
metadata:
  name: team-a-quota
  namespace: dev
spec:
  hard:
    pods: "15"             # Total pods cannot exceed 15
    requests.cpu: "2"      # Total CPU requests cannot exceed 2 cores
    requests.memory: 2Gi   # Total memory requests cannot exceed 2Gi
    limits.cpu: "4"        # Total CPU limits cannot exceed 4 cores
    limits.memory: 4Gi     # Total memory limits cannot exceed 4Gi

kubectl get quota -n dev
kubectl describe quota team-a-quota -n dev

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Limit Range for a Namespace

The max and min values in a LimitRange apply to both resource requests and limits.
You can set default minimum and maximum limits for CPU and memory for pods in a namespace. If you create or change a LimitRange, it will not affect existing pods.
  • Scope: Applies to individual containers or pods within a namespace
  • Purpose: Sets default, minimum, and maximum resource usage limits
  • Usage: Ensures each container or pod has resource requests and limits within specified bounds
cpu-limit-range.yaml
apiVersion: v1
kind: LimitRange
metadata:
  name: cpe-resource-constraint
spec:
  limits:
    - default:          # Default limits for containers
        cpu: 500m
        memory: 512Mi
      defaultRequest:   # Default requests for containers
        cpu: 500m
        memory: 512Mi
      max:              # Maximum allowed
        cpu: "1"
        memory: 1Gi
      min:              # Minimum allowed
        cpu: 100m
        memory: 256Mi
      type: Container
Example scenarios:
ConfigurationResult
No resources specifiedContainer gets 500m CPU and 512Mi memory (defaults).
Explicitly set 200m CPU and 300Mi memoryValid — within min/max range.
Explicitly set 50m CPU and 200Mi memoryFails — below the min values.
Explicitly set 2 CPU and 2Gi memoryFails — exceeds the max values.

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