Kubernetes: Namespaces

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tags: kubernetes

Namespaces

In Kubernetes, namespaces provide a mechanism for isolating groups of resources within a single cluster. Names of resources need to be unique within a namespace, but not across namespaces. Namespace-based scoping is applicable only for namespaced objects (e.g. Deployments, Services, etc) and not for cluster-wide objects (e.g. StorageClass, Nodes, PersistentVolumes, etc.).

When to Use Multiple Namespaces

Namespaces are intended for use in environments with many users spread across multiple teams, or projects.

Namespaces provide a scope for names. Names of resources need to be unique within a namespace, but not across namespaces. Namespaces cannot be nested inside one another and each Kubernetes resource can only be in one namespace.

Namespaces are a way to divide cluster resources between multiple users (via resource quota).

Initial Namespaces

  • kube-system: “for objects created by the Kubernetes system”
  • default
  • kube-public: “readable by all clients (including those not authenticated)”.
  • kube-node-lease: “holds Lease objects associated with each node”

Policies and Resource Limits

  • Each namespaces can have its own policies and resource limits so that each namespace is allocated with the allowed quota of resources.

DNS

  • Within the same namespace, each service can refer to each other by their service names (no need to specify namespace name).
    • ex: mysql.connect("db-service")
  • If a service wants to reach out to the other service in a different namespace, it’ll need to append the name of the namespace.
    • ex: mysql.connect("db-service.dev.svc.cluster.local")
    • cluster.local: domain
    • svc: service (subdomain)
    • dev: namespace
    • db-service: service name
    • When a service is created, its DNS entry is created automatically.

Commands

# Get a list of pods in a default namespace
kubectl get pods 
# Get a list of pods in a specific namespace
kubectl get pods --namespace=kube-system
# Or
kubectl get pods -n=kube-system
# Create a pod in a default namespace
kubectl create -f pod-definition.yaml
# Create a pod in a specific namespace
kubectl create -f pod-definition.yaml --namespace=dev
# Or
kubectl run <pod_name> --image=<image_name> --namespace=dev

# List all pods under all namespaces:
kubectl get pods --all-namespaces
# Or
kubectl get pods -A

# List all namespaces
kubectl get namespaces
# Or
kubectl get ns

Or, specify a namespace in a pod definition file

# pod-definition.yaml
apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
  namespace: dev
  labels:
    app: myapp
    type: front-end
spec:
  containers:
    - name: nginx-container
      image: nginx

How to Create a New Namespace

With a namespace definition file

# namespace-file.yaml
apiVersion: v1
kind: Namespace
metadata:
  name: dev
  • Run kubectl create -f namespace-file.yaml to create a new namespace

Command

kubectl create namespace dev

How to set a specific namespace as the default namespace

kubectl config set-context $(kubectl config current-context) --namespace=dev
# Or
kubectl config set-context --current --namespace=<insert-namespace-name-here>

Others

We can list all pods under all namespaces:

kubectl get pods --all-namespaces

Resource Quotas

We can limit resources in a namespace by creating a resource quota.

# resource quota definition file
apiVersion: v1
kind: ResourceQuota
metadata:
  name: resource-quota
  namespace: dev
spec:
  hard:
    pods: "5"
    requests.cpu: "4"
    requests.memory: 5Gi
    limits.cpu: "8"
    limits.memory: 10Gi

References


Copyright (c) 2025 Sunmin Kim