Why Kubernetes networking matters - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a Kubernetes Service that exposes a Pod on port 80.

Kubernetes

kubectl expose pod my-pod --port=[1]

Drag options to blanks, or click blank then click option'

A443

B80

C22

D8080

Attempts:

3 left

💡 Hint

Common Mistakes

Using port 443 which is for HTTPS, not HTTP.

Using port 22 which is for SSH.

The standard HTTP port is 80, so exposing the pod on port 80 allows web traffic.

2fill in blank

medium

Complete the command to list all Services in the default namespace.

Kubernetes

kubectl get [1]

Drag options to blanks, or click blank then click option'

Anodes

Bpods

Cservices

Ddeployments

Attempts:

3 left

💡 Hint

Common Mistakes

Listing pods instead of services.

Listing nodes which are cluster machines.

Services are listed with 'kubectl get services'.

3fill in blank

hard

Fix the error in the Service YAML to correctly specify the target port.

Kubernetes

spec:
  ports:
  - port: 80
    targetPort: [1]

Drag options to blanks, or click blank then click option'

A80

BservicePort

Chttp

DnodePort

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'http' which is not a valid port number here.

Confusing servicePort and nodePort.

The targetPort should be the port number the container listens on, usually 80 for HTTP.

4fill in blank

hard

Fill both blanks to create a NetworkPolicy that allows traffic only from pods with label 'app=frontend' to pods with label 'app=backend'.

Kubernetes

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-frontend
spec:
  podSelector:
    matchLabels:
      app: [1]
  ingress:
  - from:
    - podSelector:
        matchLabels:
          app: [2]

Drag options to blanks, or click blank then click option'

Abackend

Bfrontend

Cdatabase

Dcache

Attempts:

3 left

💡 Hint

Common Mistakes

Reversing the labels for source and destination pods.

Using unrelated labels like 'database' or 'cache'.

The policy selects pods with label 'app=backend' and allows ingress from pods labeled 'app=frontend'.

5fill in blank

hard

Fill all three blanks to define a Service of type NodePort exposing port 80 and targeting port 8080 on pods labeled 'app=web'.

Kubernetes

apiVersion: v1
kind: Service
metadata:
  name: web-service
spec:
  type: [1]
  selector:
    app: [2]
  ports:
  - port: [3]
    targetPort: 8080

Drag options to blanks, or click blank then click option'

AClusterIP

Bweb

C80

DNodePort

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'ClusterIP' which is internal only.

Mismatching selector labels.

Wrong port numbers.

The Service type should be 'NodePort' or 'LoadBalancer' to expose externally; here 'NodePort' is chosen. The selector matches pods labeled 'app=web'. The port exposed is 80, targeting 8080 on pods.

Practice

1. Why is networking important in Kubernetes clusters?

easy

A. It stores data persistently for applications.

B. It schedules Pods to nodes automatically.

C. It manages user authentication and permissions.

D. It connects different parts of applications and users.

Solution

1. Step 1: Understand Kubernetes networking role

   Kubernetes networking allows communication between application parts and external users.

2. Step 2: Differentiate networking from other functions

   Storage, authentication, and scheduling are handled by other Kubernetes components, not networking.

3. Final Answer:

   It connects different parts of applications and users. -> Option D

4. Quick Check:

   Networking = Connect apps and users [OK]

Hint: Networking links app parts and users in Kubernetes [OK]

Common Mistakes:

• Confusing networking with storage
• Mixing networking with authentication
• Thinking scheduling is networking

2. Which of the following is the correct way to expose a Pod using a Service in Kubernetes?

easy

A. kubectl service create mypod --port=80

B. kubectl expose pod mypod --port=80 --target-port=8080 --type=ClusterIP

C. kubectl create pod mypod --expose --port=80

D. kubectl expose service mypod --port=80

Solution

1. Step 1: Identify correct command to expose a Pod

   The command 'kubectl expose pod' is used to expose a Pod as a Service with specified ports and type.

2. Step 2: Check syntax correctness

   kubectl expose pod mypod --port=80 --target-port=8080 --type=ClusterIP uses correct syntax with --port, --target-port, and --type flags. Other options use invalid commands or flags.

3. Final Answer:

   kubectl expose pod mypod --port=80 --target-port=8080 --type=ClusterIP -> Option B

4. Quick Check:

   Expose Pod = kubectl expose pod [OK]

Hint: Use 'kubectl expose pod' with ports and type [OK]

Common Mistakes:

• Using 'kubectl create pod' to expose
• Trying to expose a service instead of a pod
• Missing required flags like --port

3. Given the following NetworkPolicy YAML snippet, what traffic is allowed?

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

medium

A. Only frontend Pods can access backend Pods on TCP port 80.

B. No traffic is allowed to backend Pods.

C. Backend Pods can access frontend Pods on TCP port 80.

D. All Pods can access backend Pods on any port.

Solution

1. Step 1: Analyze podSelector and ingress rules

   The policy selects Pods with label role=backend and allows ingress only from Pods with role=frontend on TCP port 80.

2. Step 2: Understand traffic direction and port restrictions

   Only traffic from frontend Pods to backend Pods on TCP port 80 is allowed; other traffic is denied.

3. Final Answer:

   Only frontend Pods can access backend Pods on TCP port 80. -> Option A

4. Quick Check:

   NetworkPolicy limits ingress to frontend on port 80 [OK]

Hint: Check podSelector and ingress from labels and ports [OK]

Common Mistakes:

• Assuming all Pods can access backend
• Confusing ingress with egress
• Ignoring port restrictions

4. You created a NetworkPolicy to allow traffic only from Pods with label app=frontend to Pods with label app=backend. However, backend Pods are still accessible from other Pods. What is the likely cause?

medium

A. The NetworkPolicy is applied in the wrong namespace.

B. The NetworkPolicy is missing a podSelector, so it applies to all Pods.

C. The backend Pods do not have the label app=backend.

D. The NetworkPolicy does not specify any ingress rules, so all traffic is allowed.

Solution

1. Step 1: Verify label matching on backend Pods

   If backend Pods lack the label app=backend, the NetworkPolicy does not select them, so it does not restrict their traffic.

2. Step 2: Check other possible causes

   NetworkPolicy without ingress rules denies all traffic, missing podSelector applies to all Pods, wrong namespace means policy doesn't affect target Pods.

3. Final Answer:

   The backend Pods do not have the label app=backend. -> Option C

4. Quick Check:

   Labels must match for NetworkPolicy to apply [OK]

Hint: Check Pod labels match NetworkPolicy selectors [OK]

Common Mistakes:

• Assuming NetworkPolicy applies without matching labels
• Ignoring namespace differences
• Thinking missing ingress means allow all

5. You want to ensure that your multi-tier app in Kubernetes allows only the frontend Pods to communicate with backend Pods, and backend Pods to communicate with database Pods, but no other traffic. Which combination of Kubernetes networking features should you use?

hard

A. Use Services to expose Pods and NetworkPolicies to restrict traffic between tiers.

B. Use only Services with type LoadBalancer for all Pods.

C. Use NetworkPolicies to expose Pods externally and Services for internal traffic.

D. Use Ingress resources to control Pod-to-Pod communication.

Solution

1. Step 1: Understand role of Services and NetworkPolicies

   Services provide stable network endpoints to reach Pods, while NetworkPolicies control which Pods can communicate with each other.

2. Step 2: Apply correct features for multi-tier communication

   Use Services to expose frontend, backend, and database Pods internally. Use NetworkPolicies to restrict traffic so only allowed Pods communicate.

3. Final Answer:

   Use Services to expose Pods and NetworkPolicies to restrict traffic between tiers. -> Option A

4. Quick Check:

   Services expose; NetworkPolicies restrict traffic [OK]

Hint: Combine Services for access and NetworkPolicies for control [OK]

Common Mistakes:

• Using LoadBalancer for internal Pod communication
• Confusing Ingress with Pod-to-Pod control
• Relying only on NetworkPolicies without Services