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Lab 14: Kubernetes StatefulSet

Overview

In this lab, you'll explore Kubernetes StatefulSets, focusing on managing stateful applications with guarantees about the ordering and uniqueness of a set of Pods.

Task 1: Implement StatefulSet in Helm Chart

6 Points:

  1. Understand StatefulSets:

  2. Update Helm Chart:

    • Rename deployment.yml to statefulset.yml.
    • Create a manifest for StatefulSet following the tutorial.
    • Test with command: helm install --dry-run --debug name_of_your_chart path_to_your_chart.
    • Fix any issues and deploy it.
    • Apply best practices by moving values to variables in values.yml meaningfully.

Task 2: StatefulSet Exploration and Optimization

4 Points:

  1. Research and Documentation:

    • Create 14.md report.
    • Include the output of kubectl get po,sts,svc,pvc commands.
    • Use minikube service name_of_your_statefulset command to access your app.
    • Access the root path of your app from different tabs and modes in your browser.
    • Check the content of your file in each pod, e.g., kubectl exec pod/demo-0 -- cat visits, and provide the output for all replicas.
    • Describe and explain differences in the report.

  2. Persistent Storage Validation

    • Delete a pod:

      kubectl delete pod app-stateful-0

    • Verify that the PVC and data persist:

      kubectl get pvc
kubectl exec app-stateful-0 -- cat /data/visits

  3. Headless Service Access

    • Access pods via DNS:

      kubectl exec app-stateful-0 -- nslookup app-stateful-1.app-stateful

    • Document DNS resolution in 14.md.

  4. Monitoring & Alerts

    • Add liveness/readiness probes to your StatefulSet.
    • Describe in 14.md:
      • How probes ensure pod health.
      • Why they’re critical for stateful apps.

  5. Ordering Guarantee and Parallel Operations:

    • Explain why ordering guarantees are unnecessary for your app.
    • Implement a way to instruct the StatefulSet controller to launch or terminate all Pods in parallel.

List of Requirements:

  • Outputs of commands in 14.md.
  • Results of the "number of visits" command for each pod, with an explanation in 14.md.
  • Answers to questions in point 2 of 14.md.
  • Implementation of parallel launch and terminate.

Bonus Task: Update Strategies

2.5 Points:

  1. Apply StatefulSet to Bonus App

    • Convert your bonus app’s Helm chart to use a StatefulSet.

  2. Explore Update Strategies

    • Implement Rolling Updates:

      spec:
  updateStrategy:
    type: RollingUpdate
    rollingUpdate:
      partition: 1

    • Test Canaries: Update a subset of pods first.

    • Document in 14.md:

      • Explain OnDelete, RollingUpdate, and their use cases.
      • Compare with Deployment update strategies.

Guidelines

  • Maintain clear and organized documentation.
  • Use appropriate naming conventions for files and folders.
  • For your repository PR, ensure it's from the lab14 branch to the main branch.

Note: Understanding StatefulSets and their optimization is crucial for managing stateful applications in Kubernetes. Explore the bonus tasks to further enhance your skills.