Introduction

Network Policies in Kubernetes are a way to control the communication between pods and other network endpoints. They allow you to specify how groups of pods are allowed to communicate with each other and other network endpoints. This is crucial for securing your applications and ensuring that only the necessary communication paths are open.

Key Concepts

NetworkPolicy Resource: A Kubernetes resource used to define network policies.
Selectors: Used to specify which pods the policy applies to.
Ingress and Egress Rules: Define the allowed incoming and outgoing traffic to/from the selected pods.
Namespaces: Network policies are namespace-scoped.

Creating a Network Policy

Example: Deny All Traffic

This example demonstrates how to create a network policy that denies all incoming and outgoing traffic to a specific set of pods.

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: deny-all
  namespace: default
spec:
  podSelector: {}
  policyTypes:
  - Ingress
  - Egress

Explanation:

apiVersion: Specifies the API version.
kind: Specifies the type of resource.
metadata: Contains the name and namespace of the policy.
spec: Defines the policy rules.
- podSelector: Selects the pods to which the policy applies. An empty selector applies to all pods in the namespace.
- policyTypes: Specifies the types of traffic (Ingress and Egress) the policy applies to.

Example: Allow Specific Ingress Traffic

This example shows how to allow incoming traffic to a specific set of pods from other pods with a specific label.

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-specific-ingress
  namespace: default
spec:
  podSelector:
    matchLabels:
      app: myapp
  policyTypes:
  - Ingress
  ingress:
  - from:
    - podSelector:
        matchLabels:
          role: frontend
    ports:
    - protocol: TCP
      port: 80

Explanation:

podSelector: Selects the pods with the label app: myapp.
policyTypes: Specifies that this policy applies to Ingress traffic.
ingress: Defines the allowed incoming traffic.
- from: Specifies the source of the allowed traffic.
  - podSelector: Selects the pods with the label role: frontend.
- ports: Specifies the allowed ports and protocols.

Practical Exercise

Task

Create a network policy that allows incoming traffic to pods with the label app: backend only from pods with the label role: frontend on port 8080.

Solution

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-frontend-to-backend
  namespace: default
spec:
  podSelector:
    matchLabels:
      app: backend
  policyTypes:
  - Ingress
  ingress:
  - from:
    - podSelector:
        matchLabels:
          role: frontend
    ports:
    - protocol: TCP
      port: 8080

Explanation:

podSelector: Selects the pods with the label app: backend.
policyTypes: Specifies that this policy applies to Ingress traffic.
ingress: Defines the allowed incoming traffic.
- from: Specifies the source of the allowed traffic.
  - podSelector: Selects the pods with the label role: frontend.
- ports: Specifies the allowed port (8080) and protocol (TCP).

Common Mistakes and Tips

Empty Pod Selector: An empty podSelector applies the policy to all pods in the namespace. Be cautious when using it.
Policy Types: Always specify policyTypes to avoid confusion about whether the policy applies to Ingress, Egress, or both.
Namespace Scope: Remember that network policies are namespace-scoped. They do not apply across namespaces unless explicitly configured.

Conclusion

Network Policies are a powerful tool for securing your Kubernetes clusters by controlling pod communication. By understanding and correctly implementing network policies, you can ensure that your applications are secure and only the necessary communication paths are open. In the next module, we will explore storage options in Kubernetes, starting with Volumes.

Network Policies

Introduction

Key Concepts

Creating a Network Policy

Example: Deny All Traffic

Example: Allow Specific Ingress Traffic

Practical Exercise

Task

Solution

Common Mistakes and Tips

Conclusion

Kubernetes Course

Module 1: Introduction to Kubernetes

Module 2: Core Kubernetes Components

Module 3: Configuration and Secrets Management

Module 4: Networking in Kubernetes

Module 5: Storage in Kubernetes

Module 6: Advanced Kubernetes Concepts

Module 7: Monitoring and Logging

Module 8: Security in Kubernetes

Module 9: Scaling and Performance

Module 10: Kubernetes Ecosystem and Tools

Module 11: Case Studies and Real-World Applications

Module 12: Preparing for Kubernetes Certification