Network policies for security in Kubernetes - Mini Project: Build & Apply

Network policies for security

📖 Scenario: You are managing a Kubernetes cluster for a small company. You want to control which pods can communicate with each other to improve security.

🎯 Goal: Create a Kubernetes NetworkPolicy that allows only pods with a specific label to communicate with each other inside the same namespace.

📋 What You'll Learn

Create a NetworkPolicy YAML manifest named allow-same-label.yaml

The policy should select pods with label role: frontend

Allow ingress traffic only from pods with label role: frontend

Deny all other ingress traffic by default

💡 Why This Matters

🌍 Real World

NetworkPolicies help secure Kubernetes clusters by controlling pod communication, reducing attack surface.

💼 Career

Understanding NetworkPolicies is essential for Kubernetes administrators and DevOps engineers to enforce security best practices.

1

Create a pod selector with label role: frontend

Create a YAML manifest for a NetworkPolicy named allow-same-label.yaml with a podSelector that selects pods with the label role: frontend. Start with the apiVersion, kind, metadata, and spec fields including the podSelector.

Kubernetes

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-same-label
spec:
  podSelector:
    matchLabels:
      role: frontend
# Your code here

Hint

Use podSelector with matchLabels to select pods with label role: frontend.

2

Add ingress rule to allow traffic from pods with label role: frontend

Add an ingress rule under spec that allows traffic only from pods with the label role: frontend. Use from with podSelector inside the ingress rule.

Kubernetes

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-same-label
spec:
  podSelector:
    matchLabels:
      role: frontend
  ingress:
  # Your code here

Hint

Use ingress with a list containing from that has a podSelector matching role: frontend.

3

Set policy type to Ingress to deny all other traffic

Add policyTypes under spec and set it to - Ingress to ensure all other ingress traffic is denied by default.

Kubernetes

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-same-label
spec:
  podSelector:
    matchLabels:
      role: frontend
  ingress:
  - from:
    - podSelector:
        matchLabels:
          role: frontend
  # Your code here

Hint

Adding policyTypes: [Ingress] tells Kubernetes to deny all ingress traffic except what is allowed.

4

Apply the NetworkPolicy and verify it

Run the command kubectl apply -f allow-same-label.yaml to apply the NetworkPolicy. Then run kubectl get networkpolicy allow-same-label -o yaml to display the applied policy.

Kubernetes

# Run the apply command below
# Your code here

Hint

Use kubectl apply -f allow-same-label.yaml to create the policy and kubectl get networkpolicy allow-same-label -o yaml to verify it.

Practice

1. What is the main purpose of a Kubernetes NetworkPolicy?

easy

A. To update container images automatically

B. To schedule pods on specific nodes

C. To manage storage volumes for pods

D. To control which pods can communicate with each other

Solution

1. Step 1: Understand NetworkPolicy role

   A NetworkPolicy defines rules about pod communication inside a Kubernetes cluster.

2. Step 2: Identify main function

   It controls which pods can send or receive network traffic to improve security.

3. Final Answer:

   To control which pods can communicate with each other -> Option D

4. Quick Check:

   NetworkPolicy controls pod communication = A [OK]

Hint: NetworkPolicy controls pod communication, not scheduling or storage [OK]

Common Mistakes:

• Confusing NetworkPolicy with pod scheduling
• Thinking NetworkPolicy manages storage
• Assuming NetworkPolicy updates images

2. Which of the following is the correct way to specify a pod selector in a NetworkPolicy YAML?

easy

A. podSelector: labels: role: frontend

B. podSelector:
matchLabels:
role: frontend

C. podSelector: role=frontend

D. podSelector: role: frontend

Solution

1. Step 1: Recall podSelector syntax

   In NetworkPolicy YAML, podSelector uses matchLabels to select pods by labels.

2. Step 2: Match correct YAML format

   podSelector: matchLabels: role: frontend correctly uses podSelector with matchLabels syntax.

3. Final Answer:

   podSelector: matchLabels: role: frontend -> Option B

4. Quick Check:

   Correct podSelector uses matchLabels = C [OK]

Hint: Use matchLabels map inside podSelector for correct syntax [OK]

Common Mistakes:

• Using incorrect YAML indentation
• Omitting matchLabels key
• Writing labels without proper mapping

3. Given this NetworkPolicy snippet, what traffic is allowed?

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-nginx
spec:
  podSelector:
    matchLabels:
      app: nginx
  ingress:
  - from:
    - podSelector:
        matchLabels:
          role: frontend
    ports:
    - protocol: TCP
      port: 80

medium

A. Only pods with label role=frontend can access nginx pods on TCP port 80

B. All pods can access nginx pods on any port

C. Only pods with label app=nginx can access frontend pods on port 80

D. No traffic is allowed to nginx pods

Solution

1. Step 1: Analyze podSelector and ingress rules

   The policy selects pods with label app: nginx and allows ingress only from pods with role: frontend on TCP port 80.

2. Step 2: Interpret allowed traffic

   Only pods labeled role=frontend can connect to nginx pods on TCP port 80; other traffic is blocked.

3. Final Answer:

   Only pods with label role=frontend can access nginx pods on TCP port 80 -> Option A

4. Quick Check:

   Ingress from role=frontend on port 80 = B [OK]

Hint: Ingress from podSelector limits source pods and ports [OK]

Common Mistakes:

• Assuming all pods can access nginx
• Confusing source and destination labels
• Ignoring port restrictions

4. You wrote this NetworkPolicy but pods labeled role=frontend still cannot access app=nginx pods on port 80. What is wrong?

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-nginx
spec:
  podSelector:
    matchLabels:
      app: nginx
  ingress:
  - from:
    - podSelector:
        matchLabels:
          role: frontend
    ports:
    - protocol: TCP
      port: 8080

medium

A. The metadata name is incorrect

B. The podSelector is missing in the policy

C. The port in the policy is 8080 but nginx listens on port 80

D. The protocol TCP is not supported in NetworkPolicy

Solution

1. Step 1: Compare port in policy with actual service port

   The policy allows ingress on TCP port 8080, but nginx usually listens on port 80.

2. Step 2: Identify mismatch causing blocked traffic

   Because the port does not match nginx's listening port, traffic is blocked despite correct podSelector.

3. Final Answer:

   The port in the policy is 8080 but nginx listens on port 80 -> Option C

4. Quick Check:

   Port mismatch blocks traffic = D [OK]

Hint: Check port numbers match service and policy exactly [OK]

Common Mistakes:

• Ignoring port mismatch
• Assuming protocol TCP is unsupported
• Thinking metadata name affects traffic

5. You want to create a NetworkPolicy that allows pods labeled role=frontend to access pods labeled app=nginx on port 80, but blocks all other traffic. Which YAML snippet correctly achieves this?

hard

A. spec:
podSelector:
matchLabels:
app: nginx
ingress:
- from:
- podSelector:
matchLabels:
role: frontend
ports:
- protocol: TCP
port: 80

B. spec:
podSelector:
matchLabels:
role: frontend
ingress:
- from:
- podSelector:
matchLabels:
app: nginx
ports:
- protocol: TCP
port: 80

C. spec:
podSelector:
matchLabels:
app: nginx
egress:
- to:
- podSelector:
matchLabels:
role: frontend
ports:
- protocol: TCP
port: 80

D. spec:
podSelector:
matchLabels:
app: nginx
ingress:
- from:
- namespaceSelector:
matchLabels:
role: frontend
ports:
- protocol: TCP
port: 80

Solution

1. Step 1: Identify pods to protect and allowed sources

   The policy must select pods with app: nginx and allow ingress only from pods with role: frontend.

2. Step 2: Check ingress rules and ports

   spec: podSelector: matchLabels: app: nginx ingress: - from: - podSelector: matchLabels: role: frontend ports: - protocol: TCP port: 80 correctly uses podSelector for nginx pods and allows ingress from frontend pods on TCP port 80.

3. Step 3: Confirm other options are incorrect

   The snippet that selects role: frontend in podSelector but has from app: nginx reverses source and destination; the snippet using egress and to controls outgoing traffic; the snippet using namespaceSelector selects entire namespaces instead of specific pods.

4. Final Answer:

   spec: podSelector: matchLabels: app: nginx ingress: - from: - podSelector: matchLabels: role: frontend ports: - protocol: TCP port: 80 -> Option A

5. Quick Check:

   Correct podSelector and ingress from frontend pods = A [OK]

Hint: Select nginx pods and allow ingress from frontend pods on port 80 [OK]

Common Mistakes:

• Mixing up podSelector labels
• Using egress instead of ingress
• Using namespaceSelector instead of podSelector