Module Review

You’ve mastered the art of Kubernetes Scaling. From pod-level resizing to cluster-wide expansion, let’s solidify these concepts.

Key Takeaways

  1. HPA Scales Out: It adds replicas based on utilization = current / request. It needs resources.requests to be set.
  2. VPA Scales Up: It changes pod requests based on historical usage. It requires pod restart (unless updateMode: Off).
  3. CA Scales Nodes: It reacts to Pending Pods, not high CPU. It adds nodes when pods can’t schedule.
  4. Metrics Server is Critical: It’s the source of truth for HPA/VPA. It holds no history (last 60s only).

  5. DaemonSets are Unique: They bypass the scheduler’s replica count logic to ensure one pod per node.

Module Review: Scaling & Operations

[!NOTE] This module explores the core principles of Module Review: Scaling & Operations, deriving solutions from first principles and hardware constraints to build world-class, production-ready expertise.

1. Flashcards

Test your recall. Click to flip.

What triggers the Cluster Autoscaler?

(Click to reveal)

Pending Pods

CA only scales up when a pod cannot be scheduled due to insufficient resources. It does NOT scale on high CPU usage alone.

Why is HPA + VPA on CPU dangerous?

Feedback Loop

HPA adds pods on high CPU. VPA increases requests on high CPU. This leads to larger pods AND more replicas, wasting resources.

What happens if `resources.requests` is missing?

HPA Fails

HPA cannot calculate utilization percentage without a request value. CPU scaling will not work.

Does Metrics Server store history?

No

It only stores the latest scrape (window of ~60s). For history, you need Prometheus.

How do you run a pod on the Master node?

Tolerations

You must add a `toleration` for the `node-role.kubernetes.io/master:NoSchedule` taint.

2. Cheat Sheet: The Scaling Triad

Feature HPA VPA Cluster Autoscaler
Direction Horizontal (More Replicas) Vertical (Larger Replicas) Infrastructure (More Nodes)
Trigger CPU/Mem Utilization > Target Historical Usage > Request Pending Pods
Action Updates replicas in Deployment Updates requests in Pod Spec Calls Cloud Provider API
Downtime None (Zero downtime) Yes (Pod Restart) None (for existing pods)
Best For Stateless Microservices Java Apps / Databases / Monoliths Any Cluster

3. Next Steps

Now that your cluster scales perfectly, how do you secure it?

Next Module: Security & RBAC