Cluster upgrade strategies in Kubernetes - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Rolling Upgrade Strategy

Which statement best describes the rolling upgrade strategy in Kubernetes cluster upgrades?

A Upgrade nodes one at a time, maintaining cluster availability throughout.

B Upgrade all nodes simultaneously, causing a brief downtime.

C Upgrade only the master nodes and leave worker nodes unchanged.

D Upgrade nodes randomly without any order or plan.

💡 Hint

Think about how to keep the cluster available during upgrades.

The rolling upgrade strategy upgrades nodes one by one, ensuring the cluster remains available without downtime.

💻 Command Output

intermediate

Output of draining a node before upgrade

What is the expected output when running kubectl drain node-1 --ignore-daemonsets --delete-local-data?

Kubernetes

kubectl drain node-1 --ignore-daemonsets --delete-local-data

A Warning: ignoring DaemonSet-managed pods: kube-proxy, fluentd

B Error from server (NotFound): nodes "node-1" not found

C node/node-1 cordoned and drained

D node/node-1 drained

💡 Hint

Draining a node marks it unschedulable and evicts pods.

The command cordons the node (marks unschedulable) and drains pods, so the output confirms both actions.

🔀 Workflow

advanced

Correct sequence for a blue-green cluster upgrade

What is the correct order of steps in a blue-green upgrade strategy for Kubernetes clusters?

A 1,3,2,4

B 1,2,3,4

C 2,1,3,4

D 3,1,2,4

💡 Hint

Think about deploying, testing, switching traffic, then removing old cluster.

First deploy green cluster, then test it, switch traffic, and finally remove blue cluster.

❓ Troubleshoot

advanced

Troubleshooting node upgrade failure due to pod eviction

During a node upgrade, kubectl drain fails with the error: error when evicting pod: pods "my-pod" is not managed by a controller. What is the most likely cause?

A The pod has completed successfully and is terminating.

B The node is already drained and cordoned.

C The pod is managed by a ReplicaSet controller.

D The pod is a static pod and cannot be evicted automatically.

💡 Hint

Pods not managed by controllers are harder to evict.

Static pods are created directly by kubelet and are not managed by controllers, so they cannot be evicted by drain.

✅ Best Practice

expert

Best practice for minimizing downtime during cluster upgrade

Which practice best minimizes downtime during a Kubernetes cluster upgrade?

A Upgrade all nodes at once during a maintenance window.

B Use a rolling upgrade with pod disruption budgets configured.

C Delete all pods before upgrading nodes to avoid conflicts.

D Upgrade only worker nodes and skip control plane nodes.

💡 Hint

Consider how to keep pods available during node upgrades.

Using rolling upgrades with pod disruption budgets ensures pods remain available and downtime is minimized.

Practice

1. What is the recommended order when upgrading a Kubernetes cluster?

easy

A. Upgrade all nodes simultaneously

B. Upgrade worker nodes first, then control plane nodes

C. Upgrade control plane nodes first, then worker nodes

D. Upgrade only the worker nodes

Solution

1. Step 1: Understand the role of control plane nodes

   Control plane nodes manage the cluster state and API server, so they must be stable first.

2. Step 2: Upgrade worker nodes after control plane

   Worker nodes run workloads and depend on the control plane, so upgrade them after control plane nodes.

3. Final Answer:

   Upgrade control plane nodes first, then worker nodes -> Option C

4. Quick Check:

   Control plane first, workers second = A [OK]

Hint: Always upgrade control plane nodes before worker nodes [OK]

Common Mistakes:

• Upgrading worker nodes before control plane
• Upgrading all nodes at once causing downtime
• Skipping control plane upgrade

2. Which command correctly drains a node before upgrading it?

easy

A. kubectl drain --ignore-daemonsets --delete-local-data

B. kubectl upgrade node

C. kubectl delete node

D. kubectl cordon --force

Solution

1. Step 1: Identify the correct drain command syntax

   The command to safely evict pods is 'kubectl drain' with flags to ignore daemonsets and delete local data.

2. Step 2: Verify other options are incorrect

   Upgrade and delete commands do not drain nodes; cordon only marks unschedulable but does not evict pods.

3. Final Answer:

   kubectl drain <node-name> --ignore-daemonsets --delete-local-data -> Option A

4. Quick Check:

   Drain command with correct flags = A [OK]

Hint: Use 'kubectl drain' with flags to safely evict pods [OK]

Common Mistakes:

• Using 'kubectl cordon' instead of 'drain'
• Deleting nodes instead of draining
• Missing flags causing pod eviction failure

3. Given this upgrade sequence, what is the expected cluster state?

1. Drain node1
2. Upgrade node1
3. Uncordon node1
4. Repeat for node2 and node3

medium

A. Control plane nodes are upgraded last

B. Cluster remains available with minimal downtime

C. Pods are deleted permanently during upgrade

D. Cluster goes down during node upgrades

Solution

1. Step 1: Analyze the upgrade steps

   Each node is drained to safely evict pods, upgraded, then uncordoned to resume scheduling.

2. Step 2: Understand impact on cluster availability

   Upgrading nodes one by one with draining keeps workloads running on other nodes, minimizing downtime.

3. Final Answer:

   Cluster remains available with minimal downtime -> Option B

4. Quick Check:

   Draining and upgrading nodes one by one = D [OK]

Hint: Upgrade nodes one at a time with drain/un-cordon for uptime [OK]

Common Mistakes:

• Assuming cluster goes down during upgrades
• Not draining nodes causing pod failures
• Upgrading all nodes simultaneously

4. You ran kubectl drain node1 but pods did not evict. What is the likely cause?

medium

A. DaemonSet pods are blocking eviction

B. Node is already uncordoned

C. Control plane node cannot be drained

D. Pods have no local storage

Solution

1. Step 1: Understand drain behavior with DaemonSets

   By default, drain blocks if DaemonSet pods are running unless --ignore-daemonsets is used.

2. Step 2: Check other options for correctness

   Uncordon status does not block eviction; control plane nodes can be drained; pods without local storage do not block drain.

3. Final Answer:

   DaemonSet pods are blocking eviction -> Option A

4. Quick Check:

   DaemonSet pods block drain without flag = C [OK]

Hint: Use --ignore-daemonsets flag to drain nodes with DaemonSet pods [OK]

Common Mistakes:

• Not using --ignore-daemonsets flag
• Confusing cordon with drain
• Assuming control plane nodes cannot be drained

5. You want to upgrade a large Kubernetes cluster with minimal downtime. Which strategy is best?

hard

A. Upgrade all control plane nodes simultaneously, then all workers simultaneously

B. Skip draining and upgrade nodes in random order

C. Drain all nodes at once, upgrade, then uncordon all nodes

D. Use cloud provider upgrade tools to upgrade control plane, then drain and upgrade workers one by one

Solution

1. Step 1: Consider cloud provider tools for control plane upgrade

   Cloud tools often automate safe control plane upgrades reducing manual errors.

2. Step 2: Upgrade worker nodes one by one with drain/un-cordon

   This approach avoids downtime by keeping workloads running on other nodes during upgrade.

3. Step 3: Evaluate other options for risks

   Upgrading all nodes simultaneously or skipping drain risks downtime and pod failures.

4. Final Answer:

   Use cloud provider upgrade tools to upgrade control plane, then drain and upgrade workers one by one -> Option D

5. Quick Check:

   Cloud tools + sequential worker upgrade = B [OK]

Hint: Use cloud tools and upgrade workers one at a time with drain [OK]

Common Mistakes:

• Upgrading all nodes simultaneously causing downtime
• Skipping drain causing pod disruption
• Ignoring cloud provider upgrade features