Deep Dive into Kubernetes Namespaces#

Kubernetes Namespaces provide a mechanism for isolating groups of resources within a single cluster. In this hands-on exercise, we’ll explore Namespaces in depth by creating multiple Kubernetes resources and examining how they interact across namespace boundaries.

What are Kubernetes Namespaces?#

Namespaces in Kubernetes serve several important purposes:

Provide isolation of resources
Help avoid accidental deletion or modification of resources
Allow separation of resources by type, environment, domain, etc.
Enable resources to access each other within the same namespace using their first name, while requiring fully qualified domain names (FQDNs) for cross-namespace communication

Let’s dive into our hands-on exercise to see these concepts in action.

Hands-on Exercise#

Step 1: Create Namespaces#

First, let’s create two namespaces:

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kubectl create namespace ns1
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kubectl create namespace ns2

Step 2: Create Deployments#

Now, let’s create a deployment in each namespace:

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apiVersion: apps/v1
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kind: Deployment
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metadata:
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  name: deploy-ns1
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  namespace: ns1
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spec:
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  replicas: 1
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  selector:
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    matchLabels:
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      app: nginx-ns1
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  template:
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    metadata:
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      labels:
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        app: nginx-ns1
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    spec:
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      containers:
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        - name: nginx
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          image: nginx

Save this as deploy-ns1.yaml and create a similar file for ns2. Then apply both:

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kubectl apply -f deploy-ns1.yaml
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kubectl apply -f deploy-ns2.yaml

Step 3: Get Pod IP Addresses#

Retrieve the IP addresses of the pods:

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kubectl get pods -n ns1 -o wide
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kubectl get pods -n ns2 -o wide

Step 4: Test Pod-to-Pod Communication#

Exec into the pod in ns1 and curl the pod in ns2:

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kubectl exec -it -n ns1 $(kubectl get pod -n ns1 -o jsonpath='{.items[0].metadata.name}') -- /bin/bash
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curl <IP-of-pod-in-ns2>

This should return the nginx welcome page.

Step 5: Scale Deployments#

Scale both deployments to 3 replicas:

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kubectl scale deployment -n ns1 deploy-ns1 --replicas=3
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kubectl scale deployment -n ns2 deploy-ns2 --replicas=3

Step 6: Create Services#

Create services to expose the deployments:

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apiVersion: v1
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kind: Service
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metadata:
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  name: svc-ns1
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  namespace: ns1
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spec:
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  selector:
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    app: nginx-ns1
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  ports:
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    - protocol: TCP
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      port: 80
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      targetPort: 80

Create a similar file for ns2 and apply both:

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kubectl apply -f svc-ns1.yaml
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kubectl apply -f svc-ns2.yaml

Step 7: Test Pod-to-Service Communication#

Exec into a pod in ns1 and curl the service in ns2:

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kubectl exec -it -n ns1 $(kubectl get pod -n ns1 -o jsonpath='{.items[0].metadata.name}') -- /bin/bash
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curl <IP-of-svc-in-ns2>

This should work and return the nginx welcome page.

Step 8: Test Service Name Resolution#

Try to curl the service using just its name:

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curl svc-ns2

This will fail with a name resolution error.

Step 9: Test FQDN Service Name Resolution#

Now, try using the Fully Qualified Domain Name (FQDN) of the service:

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curl svc-ns2.ns2.svc.cluster.local

This should work and return the nginx welcome page.

Step 10: Clean Up#

Delete both namespaces to clean up all resources:

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kubectl delete namespace ns1
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kubectl delete namespace ns2

Key Takeaways#

Namespace Isolation: Namespaces provide a level of isolation between resources.
Cross-Namespace Communication: Pods can communicate across namespaces using IP addresses or FQDNs.
DNS Resolution: Within a namespace, services can be reached by their short names. Across namespaces, FQDNs are required.
Resource Management: Deleting a namespace removes all resources within it, simplifying cleanup.

Conclusion#

Kubernetes Namespaces are a powerful feature for organizing and isolating resources within a cluster. They provide a way to divide cluster resources between multiple users and are essential for multi-tenant environments. Understanding how to work with and communicate across namespaces is crucial for effective Kubernetes management and application design.

References#

DNS Resolution: service-name.namespace.svc.cluster.local