Learn Kubernetes Basics

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Declare Network Policy

This document helps you get started using the Kubernetes NetworkPolicy API to declare network policies that govern how pods communicate with each other.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:

To check the version, enter kubectl version.

Make sure you’ve configured a network provider with network policy support. There are a number of network providers that support NetworkPolicy, including:

Note: The above list is sorted alphabetically by product name, not by recommendation or preference. This example is valid for a Kubernetes cluster using any of these providers.

Create an nginx deployment and expose it via a service

To see how Kubernetes network policy works, start off by creating an nginx deployment.

kubectl run nginx --image=nginx --replicas=2
deployment.apps/nginx created

And expose it via a service.

kubectl expose deployment nginx --port=80
service/nginx exposed

This runs two nginx pods in the default namespace, and exposes them through a service called nginx.

kubectl get svc,pod
NAME                        CLUSTER-IP    EXTERNAL-IP   PORT(S)    AGE
service/kubernetes          10.100.0.1    <none>        443/TCP    46m
service/nginx               10.100.0.16   <none>        80/TCP     33s

NAME                        READY         STATUS        RESTARTS   AGE
pod/nginx-701339712-e0qfq   1/1           Running       0          35s
pod/nginx-701339712-o00ef   1/1           Running       0          35s

Test the service by accessing it from another pod

You should be able to access the new nginx service from other pods. To test, access the service from another pod in the default namespace. Make sure you haven’t enabled isolation on the namespace.

Start a busybox container, and use wget on the nginx service:

kubectl run busybox --rm -ti --image=busybox /bin/sh
Waiting for pod default/busybox-472357175-y0m47 to be running, status is Pending, pod ready: false

Hit enter for command prompt

/ # wget --spider --timeout=1 nginx
Connecting to nginx (10.100.0.16:80)
/ #

Limit access to the nginx service

Let’s say you want to limit access to the nginx service so that only pods with the label access: true can query it. To do that, create a NetworkPolicy that allows connections only from those pods:

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: access-nginx
spec:
  podSelector:
    matchLabels:
      run: nginx
  ingress:
  - from:
    - podSelector:
        matchLabels:
          access: "true"

Assign the policy to the service

Use kubectl to create a NetworkPolicy from the above nginx-policy.yaml file:

kubectl apply -f nginx-policy.yaml
networkpolicy.networking.k8s.io/access-nginx created

Test access to the service when access label is not defined

If we attempt to access the nginx Service from a pod without the correct labels, the request will now time out:

kubectl run busybox --rm -ti --image=busybox /bin/sh
Waiting for pod default/busybox-472357175-y0m47 to be running, status is Pending, pod ready: false

Hit enter for command prompt

/ # wget --spider --timeout=1 nginx
Connecting to nginx (10.100.0.16:80)
wget: download timed out
/ #

Define access label and test again

Create a pod with the correct labels, and you’ll see that the request is allowed:

kubectl run busybox --rm -ti --labels="access=true" --image=busybox /bin/sh
Waiting for pod default/busybox-472357175-y0m47 to be running, status is Pending, pod ready: false

Hit enter for command prompt

/ # wget --spider --timeout=1 nginx
Connecting to nginx (10.100.0.16:80)
/ #

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