Container Network Interface (CNI) in Kubernetes - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of the Container Network Interface (CNI) in Kubernetes?

CNI provides a standard way to configure network interfaces for containers, enabling them to communicate within a Kubernetes cluster.

beginner

Name two popular CNI plugins used in Kubernetes.

Calico and Flannel are two popular CNI plugins that provide networking capabilities for Kubernetes clusters.

intermediate

How does CNI help with container IP address management?

CNI plugins allocate and assign IP addresses to containers, ensuring each container has a unique IP for communication.

intermediate

What file format does CNI use to define network configurations?

CNI uses JSON files to define network configurations that specify how container interfaces should be set up.

intermediate

Explain the role of the CNI plugin during pod creation in Kubernetes.

When a pod is created, the CNI plugin is called to set up the network interface, assign an IP, and connect the pod to the cluster network.

What does CNI stand for in Kubernetes networking?

A Container Network Interface

B Cluster Node Integration

C Container Node Interaction

D Cluster Network Interface

CNI stands for Container Network Interface, which standardizes container networking.

Which file format is used to configure CNI plugins?

A YAML

B JSON

C XML

D INI

CNI configurations are defined using JSON files.

Which of the following is NOT a CNI plugin?

A Calico

B Weave Net

C Flannel

D Docker Swarm

Docker Swarm is a container orchestration tool, not a CNI plugin.

What is the role of a CNI plugin when a pod starts?

A Assign IP and configure network interface

B Create storage volumes

C Schedule the pod on a node

D Monitor pod health

CNI plugins assign IP addresses and set up network interfaces for pods.

Why is CNI important in Kubernetes?

A It schedules pods

B It manages container storage

C It standardizes container networking

D It monitors cluster health

CNI standardizes how container networking is configured and managed.

Describe what the Container Network Interface (CNI) does in a Kubernetes cluster.

Think about how containers get connected inside the cluster.

List some common CNI plugins and explain why you might choose one over another.

Consider what features or needs your cluster might have.

Practice

1. What is the main purpose of the Container Network Interface (CNI) in Kubernetes?

easy

A. To manage storage volumes for containers

B. To provide IP addresses and networking for pods

C. To schedule pods on nodes

D. To monitor container resource usage

Solution

1. Step 1: Understand CNI role in Kubernetes

   CNI is responsible for setting up networking so pods can communicate.

2. Step 2: Identify correct function

   Providing IP addresses and network connectivity to pods is the core function of CNI.

3. Final Answer:

   To provide IP addresses and networking for pods -> Option B

4. Quick Check:

   CNI = Pod networking [OK]

Hint: CNI is about pod networking, not storage or scheduling [OK]

Common Mistakes:

• Confusing CNI with storage management
• Thinking CNI schedules pods
• Assuming CNI monitors resources

2. Which of the following is a valid CNI configuration file format?

easy

A. XML

B. CSV

C. INI

D. JSON

Solution

1. Step 1: Recall CNI config formats

   CNI plugins use JSON or YAML files to configure networking.

2. Step 2: Identify valid format

   JSON is the standard format for CNI configuration files.

3. Final Answer:

   JSON -> Option D

4. Quick Check:

   CNI config = JSON [OK]

Hint: CNI configs are JSON or YAML, not XML or INI [OK]

Common Mistakes:

• Choosing XML as config format
• Confusing INI or CSV with CNI config
• Not knowing CNI uses JSON

3. Given this CNI config snippet:

{
  "cniVersion": "0.4.0",
  "name": "mynet",
  "type": "bridge",
  "bridge": "cni0",
  "ipMasq": true,
  "ipam": {
    "type": "host-local",
    "subnet": "10.22.0.0/16"
  }
}

What IP subnet will pods get addresses from?

medium

A. 172.16.0.0/12

B. 192.168.1.0/24

C. 10.22.0.0/16

D. None, IPs are assigned dynamically

Solution

1. Step 1: Locate subnet in config

   The subnet is specified inside the "ipam" section as "10.22.0.0/16".

2. Step 2: Understand IP assignment

   Pods will get IPs from the defined subnet range in the config.

3. Final Answer:

   10.22.0.0/16 -> Option C

4. Quick Check:

   Subnet in ipam = 10.22.0.0/16 [OK]

Hint: Look inside "ipam" for subnet to find pod IP range [OK]

Common Mistakes:

• Ignoring the subnet field
• Choosing default Kubernetes pod subnet
• Thinking IPs are random without subnet

4. You installed a CNI plugin but pods cannot communicate across nodes. What is a likely cause?

medium

A. CNI config file missing or incorrect

B. Pods have no CPU limits set

C. Kubernetes API server is down

D. Node disk space is full

Solution

1. Step 1: Analyze pod network failure

   Pods not communicating across nodes usually means network setup is broken.

2. Step 2: Check CNI config

   If the CNI config file is missing or wrong, networking won't work properly.

3. Final Answer:

   CNI config file missing or incorrect -> Option A

4. Quick Check:

   Network issues = CNI config problem [OK]

Hint: Check CNI config file first for network issues [OK]

Common Mistakes:

• Blaming CPU limits for network problems
• Assuming API server affects pod networking directly
• Ignoring CNI config correctness

5. You want to deploy a new CNI plugin that supports network policies and IP address management. Which step is NOT required?

hard

A. Restart the Kubernetes API server

B. Create a CNI configuration file in /etc/cni/net.d/

C. Install the CNI plugin binaries on all nodes

D. Ensure kubelet is configured to use the new CNI

Solution

1. Step 1: Understand CNI plugin deployment steps

   You must install plugin binaries, add config files, and configure kubelet to use it.

2. Step 2: Identify unnecessary step

   Restarting the Kubernetes API server is not needed for CNI plugin changes.

3. Final Answer:

   Restart the Kubernetes API server -> Option A

4. Quick Check:

   API server restart NOT needed for CNI install [OK]

Hint: API server restart not needed when changing CNI [OK]

Common Mistakes:

• Thinking API server restart is required
• Forgetting to install plugin binaries
• Not placing config in correct directory