#Kubernetes Architecture & Core Concepts¶

Kubernetes (K8s) is the industry-standard container orchestration platform. It automates deployment, scaling, and management of containerised applications.

Why Kubernetes?¶

Running one container on one server is easy. Running thousands of containers across hundreds of servers is not. Kubernetes solves:

Scheduling — which containers run on which nodes?
Self-healing — restart failed containers automatically
Scaling — add more instances when load increases
Rolling updates — deploy new versions with zero downtime
Service discovery — containers find each other by name, not IP

The Control Plane¶

┌─────────────────────────────────────────────────┐
│               Kubernetes Cluster                 │
│                                                  │
│  ┌─────────────────────────────────────────┐    │
│  │            Control Plane                 │    │
│  │  ┌──────────┐  ┌───────┐  ┌──────────┐  │    │
│  │  │ API Server│  │  etcd │  │ Scheduler│  │    │
│  │  └──────────┘  └───────┘  └──────────┘  │    │
│  └─────────────────────────────────────────┘    │
│                                                  │
│  ┌──────────┐    ┌──────────┐    ┌──────────┐   │
│  │  Node 1  │    │  Node 2  │    │  Node 3  │   │
│  │ ┌──────┐ │    │ ┌──────┐ │    │ ┌──────┐ │   │
│  │ │ Pod  │ │    │ │ Pod  │ │    │ │ Pod  │ │   │
│  │ └──────┘ │    │ └──────┘ │    │ └──────┘ │   │
│  └──────────┘    └──────────┘    └──────────┘   │
└─────────────────────────────────────────────────┘

Core Objects¶

Pod¶

The smallest deployable unit — one or more containers that share networking and storage.

yaml

10 lines

1apiVersion: v1
2kind: Pod
3metadata:
4  name: my-app
5spec:
6  containers:
7  - name: app
8    image: my-app:1.0
9    ports:
10    - containerPort: 3000

Deployment¶

Manages a set of identical Pods. Handles rolling updates and rollbacks.

yaml

26 lines

1apiVersion: apps/v1
2kind: Deployment
3metadata:
4  name: my-app
5spec:
6  replicas: 3              # Run 3 Pods
7  selector:
8    matchLabels:
9      app: my-app
10  template:
11    metadata:
12      labels:
13        app: my-app
14    spec:
15      containers:
16      - name: app
17        image: my-app:1.0
18        ports:
19        - containerPort: 3000
20        resources:
21          requests:
22            cpu: "100m"
23            memory: "128Mi"
24          limits:
25            cpu: "250m"
26            memory: "256Mi"

Service¶

Provides a stable network endpoint to reach a set of Pods.

yaml

11 lines

1apiVersion: v1
2kind: Service
3metadata:
4  name: my-app-svc
5spec:
6  selector:
7    app: my-app
8  ports:
9  - port: 80
10    targetPort: 3000
11  type: ClusterIP    # or LoadBalancer for external access

Essential kubectl Commands¶

bash

8 lines

1kubectl get pods                     # List pods
2kubectl get deployments              # List deployments
3kubectl describe pod my-app          # Detailed info
4kubectl logs my-app-abc123           # Pod logs
5kubectl exec -it my-app-abc123 -- sh # Shell into pod
6kubectl apply -f deployment.yaml     # Apply config
7kubectl scale deploy/my-app --replicas=5  # Scale up
8kubectl rollout undo deploy/my-app   # Rollback

Why Kubernetes?¶

Running one container on one server is easy. Running thousands of containers across hundreds of servers is not. Kubernetes solves:

Scheduling — which containers run on which nodes?

Self-healing — restart failed containers automatically

Scaling — add more instances when load increases

Rolling updates — deploy new versions with zero downtime

Service discovery — containers find each other by name, not IP

The Control Plane¶

┌─────────────────────────────────────────────────┐ │ Kubernetes Cluster │ │ │ │ ┌─────────────────────────────────────────┐ │ │ │ Control Plane │ │ │ │ ┌──────────┐ ┌───────┐ ┌──────────┐ │ │ │ │ │ API Server│ │ etcd │ │ Scheduler│ │ │ │ │ └──────────┘ └───────┘ └──────────┘ │ │ │ └─────────────────────────────────────────┘ │ │ │ │ ┌──────────┐ ┌──────────┐ ┌──────────┐ │ │ │ Node 1 │ │ Node 2 │ │ Node 3 │ │ │ │ ┌──────┐ │ │ ┌──────┐ │ │ ┌──────┐ │ │ │ │ │ Pod │ │ │ │ Pod │ │ │ │ Pod │ │ │ │ │ └──────┘ │ │ └──────┘ │ │ └──────┘ │ │ │ └──────────┘ └──────────┘ └──────────┘ │ └─────────────────────────────────────────────────┘

Core Objects¶

The smallest deployable unit — one or more containers that share networking and storage.

yaml

10 lines

1apiVersion: v1
2kind: Pod
3metadata:
4  name: my-app
5spec:
6  containers:
7  - name: app
8    image: my-app:1.0
9    ports:
10    - containerPort: 3000

Deployment¶

Manages a set of identical Pods. Handles rolling updates and rollbacks.

yaml

26 lines

1apiVersion: apps/v1
2kind: Deployment
3metadata:
4  name: my-app
5spec:
6  replicas: 3              # Run 3 Pods
7  selector:
8    matchLabels:
9      app: my-app
10  template:
11    metadata:
12      labels:
13        app: my-app
14    spec:
15      containers:
16      - name: app
17        image: my-app:1.0
18        ports:
19        - containerPort: 3000
20        resources:
21          requests:
22            cpu: "100m"
23            memory: "128Mi"
24          limits:
25            cpu: "250m"
26            memory: "256Mi"

Service¶

Provides a stable network endpoint to reach a set of Pods.

yaml

11 lines

1apiVersion: v1
2kind: Service
3metadata:
4  name: my-app-svc
5spec:
6  selector:
7    app: my-app
8  ports:
9  - port: 80
10    targetPort: 3000
11  type: ClusterIP    # or LoadBalancer for external access

Essential kubectl Commands¶

bash

8 lines

1kubectl get pods                     # List pods
2kubectl get deployments              # List deployments
3kubectl describe pod my-app          # Detailed info
4kubectl logs my-app-abc123           # Pod logs
5kubectl exec -it my-app-abc123 -- sh # Shell into pod
6kubectl apply -f deployment.yaml     # Apply config
7kubectl scale deploy/my-app --replicas=5  # Scale up
8kubectl rollout undo deploy/my-app   # Rollback