Container Network Interface (CNI) in Kubernetes - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the CNI plugin in a Kubernetes pod network configuration.

Kubernetes

cniVersion: "0.3.1"
name: my-network
plugins:
  - type: [1]

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

Abridge

Bdocker

Chost

Dproxy

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'docker' which is not a CNI plugin type

Using 'host' which is a network mode, not a plugin type

The bridge plugin is a common CNI plugin used to create a network bridge for pods.

2fill in blank

medium

Complete the code to assign IP addresses dynamically using the CNI IPAM plugin.

Kubernetes

{
  "cniVersion": "0.3.1",
  "name": "my-network",
  "plugins": [
    {
      "type": "bridge",
      "ipam": {
        "type": [1]
      }
    }
  ]
}

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

Ahost-local

Bdhcp

Cstatic

Dmanual

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'static' which requires manual IP assignment

Using 'dhcp' which is not commonly used in Kubernetes CNI

The host-local IPAM plugin assigns IP addresses dynamically from a local range.

3fill in blank

hard

Fix the error in the CNI configuration by completing the missing field for the bridge name.

Kubernetes

{
  "cniVersion": "0.3.1",
  "name": "my-network",
  "plugins": [
    {
      "type": "bridge",
      "bridge": [1],
      "ipam": {
        "type": "host-local"
      }
    }
  ]
}

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

Aeth0

Bcni0

C"eth0"

D"cni0"

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting quotes causing JSON syntax errors

Using interface names like 'eth0' instead of bridge names

The bridge field requires the bridge name as a string, so it must be quoted like "cni0".

4fill in blank

hard

Fill both blanks to configure a CNI plugin with a bridge name and subnet for IPAM.

Kubernetes

{
  "cniVersion": "0.3.1",
  "name": "my-network",
  "plugins": [
    {
      "type": "bridge",
      "bridge": [1],
      "ipam": {
        "type": "host-local",
        "subnet": [2]
      }
    }
  ]
}

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

A"br0"

B"192.168.1.0/24"

C"10.1.0.0/16"

D"eth1"

Attempts:

3 left

💡 Hint

Common Mistakes

Using interface names instead of bridge names

Providing subnet without quotes causing JSON errors

The bridge name should be a string like "br0", and the subnet must be a valid CIDR string like "192.168.1.0/24".

5fill in blank

hard

Fill all three blanks to create a CNI config with bridge type, IPAM subnet, and gateway.

Kubernetes

{
  "cniVersion": "0.3.1",
  "name": "custom-net",
  "plugins": [
    {
      "type": [1],
      "bridge": [2],
      "ipam": {
        "type": "host-local",
        "subnet": [3],
        "gateway": "192.168.100.1"
      }
    }
  ]
}

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

A"bridge"

B"br-custom"

C"192.168.100.0/24"

D"eth0"

Attempts:

3 left

💡 Hint

Common Mistakes

Using unquoted strings causing JSON errors

Confusing interface names with bridge names

The plugin type is "bridge", the bridge name is "br-custom", and the subnet is "192.168.100.0/24". All must be strings in JSON.

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