What is Kubernetes Namespaces

Namespaces in Kubernetes provide a way to divide cluster resources between multiple users. They're useful in environments with many users spread across multiple teams, or when different projects share the same cluster. Think of namespaces as virtual clusters that sit on top of the same physical cluster.

Analogy

Imagine two boys named Mark, each from a different family. To avoid confusion, they are called by their last names: Mark Smith and Mark Williams. Similarly, Kubernetes uses namespaces to organize resources within a cluster, ensuring there are no naming conflicts between objects in different namespaces.

Default Namespaces

Kubernetes automatically creates three namespaces when the cluster is initialized:

default: This is where resources are created if no other namespace is specified.
kube-system: This namespace contains Kubernetes internal components like the DNS server and networking components.
kube-public: Resources in this namespace are available to all users.

Creating a Namespace

You can create your own namespaces to logically separate environments like dev, test, and production. Use the following command to create a namespace:

kubectl create namespace dev

Example output:

namespace/dev created

You can also define a namespace in a YAML configuration file:

apiVersion: v1
kind: Namespace
metadata:
  name: dev

Apply the YAML file with the following command:

kubectl apply -f namespace.yaml

Example output:

namespace/dev created

Listing All Namespaces

To list all the namespaces in your cluster, use the following command:

kubectl get namespaces

Example output:

NAME              STATUS   AGE
default           Active   24d
kube-system       Active   24d
kube-public       Active   24d
dev               Active   1h

Viewing Resources in a Namespace

To view resources, such as pods, in a specific namespace, use:

kubectl get pods -n dev

Example output:

NAME                        READY   STATUS    RESTARTS   AGE
my-app-1-7d8cfdcbfd-pqj7r    1/1     Running   0          3m
my-app-2-8476c9946b-vlqcp    1/1     Running   0          5m

Setting a Default Namespace for kubectl

If you frequently work within a specific namespace, you can set a default context for it:

kubectl config set-context --current --namespace=dev

Example output:

Context "minikube" modified.

Now, whenever you use kubectl, it will automatically operate in the dev namespace unless you specify otherwise.

Deleting a Namespace

To delete a namespace and all the resources within it, use the following command:

kubectl delete namespace dev

Example output:

namespace "dev" deleted

Namespace Resource Quotas

You can limit the resources a namespace can use by creating a resource quota. Here's an example YAML definition:

apiVersion: v1
kind: ResourceQuota
metadata:
  name: dev-quota
  namespace: dev
spec:
  hard:
    pods: "10"
    requests.cpu: "4"
    requests.memory: 8Gi
    limits.cpu: "8"
    limits.memory: 16Gi

Apply the quota with the following command:

kubectl apply -f resource-quota.yaml

Example output:

resourcequota/dev-quota created

Viewing Resource Quota Usage

To see the current usage of the resource quota in the dev namespace:

kubectl get resourcequota dev-quota -n dev --output=yaml

Example output:

apiVersion: v1
kind: ResourceQuota
metadata:
  name: dev-quota
  namespace: dev
spec:
  hard:
    limits.cpu: "8"
    limits.memory: 16Gi
    pods: "10"
    requests.cpu: "4"
    requests.memory: 8Gi
status:
  hard:
    limits.cpu: "8"
    limits.memory: 16Gi
    pods: "10"
    requests.cpu: "4"
    requests.memory: 8Gi
  used:
    limits.cpu: "2"
    limits.memory: 4Gi
    pods: "5"
    requests.cpu: "1"
    requests.memory: 2Gi