AKS networking (kubenet, Azure CNI) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is kubenet in AKS networking?

Kubenet is a basic network plugin in AKS that uses Kubernetes' own network model. It assigns IP addresses to pods from a private address space and uses network address translation (NAT) to communicate outside the cluster.

beginner

What does Azure CNI provide in AKS networking?

Azure CNI assigns IP addresses to pods directly from the Azure Virtual Network, allowing pods to have full network connectivity and be treated like regular Azure resources with their own IPs.

intermediate

What is a key difference between kubenet and Azure CNI in AKS?

Kubenet uses NAT and private IPs for pods, limiting direct access, while Azure CNI assigns real Azure VNet IPs to pods, enabling direct connectivity and better integration with Azure services.

intermediate

Why might you choose kubenet over Azure CNI in AKS?

You might choose kubenet for simpler setups or when you want to conserve IP addresses in your Azure VNet, as it uses fewer IPs by NATing pod traffic through node IPs.

intermediate

What is a limitation of Azure CNI in AKS related to IP address management?

Azure CNI requires enough free IP addresses in the Azure VNet for all pods, which can limit scalability if the subnet is small or IPs are scarce.

Which AKS networking option assigns IP addresses to pods from the Azure Virtual Network?

A kubenet

B Calico

C Flannel

D Azure CNI

Azure CNI assigns IP addresses directly from the Azure VNet to pods.

What does kubenet use to allow pods to communicate outside the cluster?

A Direct IP routing

B Load balancer

C Network Address Translation (NAT)

D VPN tunneling

Kubenet uses NAT to translate pod IPs to node IPs for external communication.

Which networking option in AKS requires more IP addresses from the Azure VNet?

A Azure CNI

B kubenet

C Both require the same

D Neither requires IP addresses

Azure CNI assigns IPs to each pod from the VNet, needing more IPs.

If you want pods to have direct network access like regular Azure resources, which AKS networking should you choose?

A kubenet

B Azure CNI

C Host networking

D Bridge networking

Azure CNI allows pods to have direct IPs on the Azure VNet.

Which AKS networking option is simpler and conserves IP addresses?

A kubenet

B Azure CNI

C Calico

D Weave

Kubenet is simpler and uses NAT, conserving IP addresses.

Explain the main differences between kubenet and Azure CNI networking options in AKS.

Think about how pods get their IP addresses and how they connect to the network.

Describe a scenario where choosing kubenet over Azure CNI would be beneficial in AKS.

Consider IP address availability and network complexity.

Practice

1. What is the main difference between kubenet and Azure CNI networking in AKS?

easy

A. Both assign IPs from the Azure subnet but differ in routing protocols.

B. Kubenet uses NAT and assigns pod IPs from a private range, Azure CNI assigns IPs from the Azure subnet directly.

C. Kubenet assigns IPs from the Azure subnet, Azure CNI uses NAT for pod IPs.

D. Azure CNI uses NAT, while kubenet assigns IPs from the Azure subnet.

Solution

1. Step 1: Understand kubenet networking

   Kubenet assigns pod IPs from a private IP range and uses NAT to allow pods to communicate outside the cluster.

2. Step 2: Understand Azure CNI networking

   Azure CNI assigns pod IPs directly from the Azure virtual network subnet, allowing pods to have direct IP addresses visible in the Azure network.

3. Final Answer:

   Kubenet uses NAT and assigns pod IPs from a private range, Azure CNI assigns IPs from the Azure subnet directly. -> Option B

4. Quick Check:

   Kubenet = NAT, Azure CNI = Azure subnet IPs [OK]

Hint: Kubenet uses NAT; Azure CNI uses Azure subnet IPs [OK]

Common Mistakes:

• Confusing which method uses NAT
• Thinking both assign IPs from Azure subnet
• Assuming Azure CNI uses private IP range

2. Which of the following is the correct way to specify Azure CNI networking when creating an AKS cluster using Azure CLI?

easy

A. az aks create --name myAKS --resource-group myRG --network-plugin azure

B. az aks create --name myAKS --resource-group myRG --network-plugin kubenet

C. az aks create --name myAKS --resource-group myRG --network-plugin azure-cni

D. az aks create --name myAKS --resource-group myRG --network-plugin azurecni

Solution

1. Step 1: Identify the correct network plugin name for Azure CNI

   The Azure CLI uses the exact string azure to specify Azure CNI networking.

2. Step 2: Check the command syntax

   The command must include --network-plugin azure to enable Azure CNI networking.

3. Final Answer:

   az aks create --name myAKS --resource-group myRG --network-plugin azure -> Option A

4. Quick Check:

   Azure CNI plugin = azure [OK]

Hint: Azure CNI plugin is exactly 'azure' in CLI [OK]

Common Mistakes:

• Using 'azure-cni' instead of 'azure'
• Confusing kubenet with Azure CNI plugin name
• Typos in the network plugin parameter

3. Given an AKS cluster configured with kubenet, what will happen if a pod tries to communicate with another pod in a different node?

medium

A. Pods communicate directly using their Azure subnet IPs without NAT.

B. Pod traffic is blocked by default between nodes.

C. Pods cannot communicate across nodes in kubenet mode.

D. The pod-to-pod traffic will be routed through the node's NAT IP and may require additional routing setup.

Solution

1. Step 1: Understand pod communication in kubenet mode

   In kubenet, pods get private IPs and use NAT on the node to communicate outside their node.

2. Step 2: Analyze cross-node pod communication

   Traffic between pods on different nodes goes through the node's NAT IP, requiring routing rules to allow this traffic.

3. Final Answer:

   The pod-to-pod traffic will be routed through the node's NAT IP and may require additional routing setup. -> Option D

4. Quick Check:

   Kubenet cross-node uses NAT routing [OK]

Hint: Kubenet pods use NAT IPs for cross-node traffic [OK]

Common Mistakes:

• Assuming direct pod IP communication in kubenet
• Thinking pods cannot communicate across nodes
• Believing pod traffic is blocked by default

4. You deployed an AKS cluster with Azure CNI but pods are not getting IP addresses from the Azure subnet. What is the likely cause?

medium

A. The Azure subnet does not have enough free IP addresses for pods.

B. The cluster was created with kubenet instead of Azure CNI.

C. The pods are configured to use host networking.

D. The Azure CNI plugin is not installed on the nodes.

Solution

1. Step 1: Check IP availability in Azure subnet

   Azure CNI assigns pod IPs from the Azure subnet. If the subnet IP pool is exhausted, pods cannot get IPs.

2. Step 2: Verify cluster network plugin and configuration

   Since the cluster is deployed with Azure CNI, the plugin is installed. Host networking would not prevent IP assignment.

3. Final Answer:

   The Azure subnet does not have enough free IP addresses for pods. -> Option A

4. Quick Check:

   Subnet IP exhaustion blocks pod IP assignment [OK]

Hint: Check subnet IP availability first for Azure CNI issues [OK]

Common Mistakes:

• Assuming plugin is missing when cluster uses Azure CNI
• Ignoring subnet IP exhaustion
• Confusing host networking with IP assignment

5. You want to deploy an AKS cluster that allows pods to communicate directly with other Azure resources in the same virtual network using their pod IPs. Which networking option should you choose and why?

hard

A. Use kubenet with additional routing rules to enable pod IP visibility.

B. Use kubenet because it saves IP addresses and allows direct pod IP communication.

C. Use Azure CNI because it assigns pod IPs from the Azure subnet enabling direct communication with Azure resources.

D. Use Azure CNI but disable IP assignment to pods for better security.

Solution

1. Step 1: Identify networking needs for direct pod-to-Azure resource communication

   Direct communication requires pods to have IPs visible in the Azure virtual network.

2. Step 2: Compare kubenet and Azure CNI capabilities

   Kubenet uses NAT and private IPs, so pods are not directly reachable. Azure CNI assigns pod IPs from the Azure subnet, enabling direct communication.

3. Final Answer:

   Use Azure CNI because it assigns pod IPs from the Azure subnet enabling direct communication with Azure resources. -> Option C

4. Quick Check:

   Azure CNI = direct pod IPs in Azure subnet [OK]

Hint: Azure CNI enables direct pod IP communication with Azure resources [OK]

Common Mistakes:

• Choosing kubenet for direct pod IP communication
• Thinking kubenet allows direct pod IP visibility
• Disabling IP assignment in Azure CNI disables communication