Kubernetes Basics

Kubernetes is simple at its core: you declare the desired state in YAML, and controllers continuously reconcile reality to match it.

Four core objects

• Pod: the smallest scheduling unit
• Deployment: manages replicas and rolling updates
• Service: stable access point
• Namespace: logical isolation boundary

Declarative model

• You describe what you want
• Controllers decide how to make it happen
• Reapplying the same YAML is safe and idempotent

Minimal Deployment example

apiVersion: apps/v1
kind: Deployment
metadata:
  name: hello
spec:
  replicas: 2
  selector:
    matchLabels:
      app: hello
  template:
    metadata:
      labels:
        app: hello
    spec:
      containers:
        - name: web
          image: nginx:1.25
          ports:
            - containerPort: 80

Common commands

• kubectl apply -f hello.yaml
• kubectl get deploy,pods
• kubectl describe deploy hello
• kubectl logs deploy/hello

Pitfalls

• Labels and selectors do not match
• Updating YAML without checking rollout status
• Treating Service as a full reverse proxy

Practical notes

• Start with a quick inventory: kubectl get nodes, kubectl get pods -A, and kubectl get events -A.
• Compare desired vs. observed state; kubectl describe usually explains drift or failed controllers.
• Keep names, labels, and selectors consistent so Services and controllers can find Pods.

Quick checklist

• The resource matches the intent you described in YAML.
• Namespaces, RBAC, and images are correct for the target environment.
• Health checks and logs are in place before promotion.

References

• Kubernetes Overview
• Workloads
• Services, Load Balancing, and Networking