🛂 Namespaces

Namespaces #

Kubernetes provides a way of logically separating resources. Kubernetes resources are either namespaced or cluster-scoped. Namespaces themselves are a resource, but namespaces are not a namespaced resource, which means that namespaces can not be put into namespaces. Namespace is a cluster-scoped resource. On the other hand all of resources we went through in the introduction are namespaced. Meaning that they will always live in the scope of a namespace.

A namespace can quickly be created using kubectl

kubectl create namespace my-namespace

A namespace can also be created by writing out the YAML resource and applying it to the cluster like we did with the Deployment earlier.

apiVersion: v1
kind: Namespace
metadata:
  name: my-namespace

Specifying namespace #

The Deployment we applied earlier didn’t specify a namespace, which caused Kubernetes to put it in the default namespace. If we want the deployment to live in a namespace other than the default, we can do one of two things.

  • Set the namespace explicitly in the metadata
  • Tell kubectl to use a specific namespace

If we set the namespace explicitly in the deployment resource, it will look something like this

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  namespace: my-namespace
  labels:
    app: nginx
spec:
  replicas: 3
  # ...

Instead explicitly setting the namespace in the Deployment we could also have used the --namespace flag when applying the resource.

kubectl apply --namespace my-namespace -f nginx-deployment.yaml

Getting the namespace name inside a pod #

The following will serve as an example of three things:

We will use the downward API to set an environment variable in the pod containing the name of the namespace in which the pod is running.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: echo-namespace
  labels:
    app: echo-namespace
spec:
  replicas: 3
  selector:
    matchLabels:
      app: echo-namespace
  template:
    metadata:
      labels:
        app: echo-namespace
    spec:
      containers:
      - name: echosvc
        image: blacksails/echosvc
        args:
        - "Hello from the namespace called '$(POD_NAMESPACE)'"
        env:
        - name: POD_NAMESPACE
          valueFrom:
            fieldRef:
              fieldPath: metadata.namespace
        ports:
        - containerPort: 8080

The downward API let’s us read fields in the resource and set their value as environment variables. The image we are running is a simple service which replies with the message that it is configured with. You can find the source code under exercises/kubernetes/namespaces.

Depending on what namespace we deploy the above example to, we will get different results when we send a request.

Exercises #

Echo namespace in different namespaces #

  • Apply the echo-namespace Deployment to two different namespaces.
  • Port-forward each of the deployments to a different port on your host machine and verify that you get a different result depending on which of the ports you hit.

When running kubectl port-forward be sure to specify the namespace using the -n/--namespace flag when you reference the deployment. Otherwise kubectl will assume the default namespace.

Echo a message from a configmap #

Instead of echoing the namespace message, change the message so that it echos another environment variable set from a configmap.

You can reuse the way that the POD_NAMESPACE variable is set. valueFrom excepts a configmap source. Take a look at the Kubernetes API reference.

August 17, 2025