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Topic 2: Deployments And ReplicaSets

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Topic 2: Deployments And ReplicaSets

Official baseline: (The Kubernetes Authors, 2026a, 2026b). My working version: A Deployment is a rollout controller. ReplicaSets are the machinery it uses to keep the right number of Pods alive.

Mental Model

A Deployment is a rollout controller. ReplicaSets are the machinery it uses to keep the right number of Pods alive.

Notes

  • The default rolling update is good until migrations or compatibility make two versions unsafe.
  • Read rollout history before guessing what changed.
  • A failed Deployment is often an image, readiness, quota, or scheduling problem.

Homelab Angle

This is the default shape for stateless homelab services: dashboards, APIs, bots, and internal tools.

Verify It

  • Read the object status before changing the manifest.
  • Check events for the controller or node that is actually complaining.
  • Confirm the official source linked below still matches the cluster version you run.

Common Failure Modes

  • Treating the YAML object as the system, instead of one input to a reconciliation loop.
  • Debugging from outside the cluster when the failure only exists inside cluster networking or node state.
  • Forgetting that Kubernetes version, addon version, and runtime behavior are linked.

Sources

  • Deployments - source path: content/en/docs/concepts/workloads/controllers/deployment.md, commit 8cc9e19b8eec8d5cf49eacd66f86a81648edb1a0.
  • ReplicaSet - source path: content/en/docs/concepts/workloads/controllers/replicaset.md, commit 8cc9e19b8eec8d5cf49eacd66f86a81648edb1a0.
  • Kubernetes documentation is licensed under CC BY 4.0; these notes are original commentary and link back to the official source.
The Kubernetes Authors. (2026a). Deployments. https://kubernetes.io/docs/concepts/workloads/controllers/deployment/
The Kubernetes Authors. (2026b). ReplicaSet. https://kubernetes.io/docs/concepts/workloads/controllers/replicaset/

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