What really happens after you run kubectl apply?

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Why this guide exists

Most Kubernetes tutorials teach you the components one at a time. You learn that Deployments manage ReplicaSets, that the Scheduler assigns Pods to nodes, that the Kubelet starts containers — and you can define each of them in isolation.

Then someone asks a simple question:

"What actually happens after you run kubectl apply?"

…and the individual definitions don't add up to an answer.

This guide takes a different approach. Instead of studying Kubernetes as a collection of independent parts, we follow one single Deployment — from the moment it leaves your terminal until a client receives a response from the running application. Every major component performs its role, then hands responsibility to the next.

The goal isn't to memorize Kubernetes. It's to understand how it thinks.

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Who it's for

• Software engineers deploying applications to Kubernetes
• DevOps engineers managing clusters
• SREs operating production workloads
• Platform engineers building internal developer platforms
• Students preparing for certifications or interviews

You don't need to be an expert. If you've written a Deployment before and know roughly what a Pod is, you have everything you need.

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The journey

kubectl apply → API Server → Authentication → Authorization → Admission Controllers
    → etcd → Deployment Controller → ReplicaSet → Pods → Scheduler → Worker Node
    → Kubelet → Container Runtime → Running Application → Service → EndpointSlice
    → kube-proxy → Client Request → Response

Every chapter is one station on that path.

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Contents

Part	Chapters
I — The Journey Begins	What Really Happens When You Run kubectl apply?
II — Entering the Cluster	The API Server · etcd: The Source of Truth
III — Kubernetes Starts Working	Understanding Controllers · The Deployment Controller · ReplicaSets
IV — Scheduling Workloads	Pods Waiting for a Home · The Scheduler · The Kubelet · Container Runtimes
V — Making Your App Reachable	The Problem with Pod IPs · Services · EndpointSlices · kube-proxy · Headless Services
VI — Self-Healing & Rolling Updates	Rolling Updates · Kubernetes Never Stops Watching
VII — Establishing Trust	Trust Between Components · Client & Server Certificates · kubeconfig
VIII — Bringing It Together	Following One Deployment From Start to Finish

Plus a Production Debugging Guide, a Component Reference, and Appendices A–E.

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Jump straight to a chapter

The reader supports deep links — handy for sharing a single answer:

Link	Topic
/#ch7	Why is my Pod stuck in Pending?
/#ch8	How the Scheduler picks a node
/#ch13	EndpointSlices — why Endpoints: <none>
/#ch14	kube-proxy, iptables, and IPVS
/#ch16	Rolling updates & zero-downtime deploys
/#debugging	Production Debugging Guide
/#reference	Every component at a glance

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Ten misconceptions this guide corrects

❌ Myth	✅ Reality
Deployments create Pods directly	Deployments create ReplicaSets; ReplicaSets create Pod objects
Kubernetes constantly polls the cluster	It's event-driven, via the Watch API
kube-proxy creates Pod networking	The CNI plugin does; kube-proxy handles Service traffic
Services own Pods	Services discover Pods using label selectors
Kubernetes runs containers	It delegates to a Container Runtime through the CRI
The Scheduler starts Pods	It only assigns them; the Kubelet starts them

…and four more inside.

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Running it locally

It's a single self-contained HTML file — no build step, no dependencies.

git clone https://github.com/<you>/inside-kubernetes.git
cd inside-kubernetes
open index.html          # macOS
# xdg-open index.html    # Linux

Fonts and diagrams are embedded, so it works fully offline.

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Repository layout

index.html                 # the book (self-contained: fonts + diagrams inlined)
inside-kubernetes.pdf      # 164-page print edition
og-image.png               # social preview card
favicon.png
robots.txt · sitemap.xml

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Contributing

Found a technical error, a typo, or a diagram that could be clearer? Open an issue — corrections are genuinely welcome.

If you're proposing a change to the text, quote the chapter and section so it's easy to locate.

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License

Released under CC BY-NC-SA 4.0.

You're free to share and adapt it with attribution, for non-commercial use.

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"Kubernetes doesn't execute commands. It reconciles desired state."

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