Deployments & Strategies

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

1. The Logic Hierarchy

You rarely create Pods directly. You create Deployments.

1. Deployment: Manages Releases (Updates, Rollbacks).
2. ReplicaSet: Manages Scale (Ensures N copies are running).
3. Pod: The actual application.

Deployment → manages → ReplicaSet → manages → Pod

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2. Update Strategies

1. RollingUpdate (Default)

Updates Pods incrementally. Zero Downtime.

• MaxUnavailable: How many pods can be down during update (e.g., 25%).
• MaxSurge: How many extra pods can be created (e.g., 25%).

2. Recreate

Kills ALL old pods, then starts ALL new pods.

• Downtime: Yes.
• Use Case: Database schema changes where versions cannot coexist.

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3. Interactive: Rolling Update Simulator

Watch how v1 is replaced by v2 without downtime.

Cluster State

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4. Rollbacks

Mistake in v2? Undo it instantly. kubectl rollout undo deployment/my-app

Kubernetes keeps a history of ReplicaSets. It basically scales v1 RS up and v2 RS down.

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5. Code Example: Deployment YAML

Diff

Full YAML

 apiVersion: apps/v1
 kind: Deployment
 metadata:
   name: backend
 spec:
   replicas: 3
   template:
   spec:
     containers:
-      - image: my-app:v1
+      - image: my-app:v2

apiVersion: apps/v1
kind: Deployment
metadata:
  name: backend
spec:
  replicas: 3
  selector:
  matchLabels:
    app: backend
  strategy:
  type: RollingUpdate
  rollingUpdate:
    maxSurge: 1
    maxUnavailable: 0
  template:
  metadata:
    labels:
    app: backend
  spec:
    containers:
    - name: server
    image: nginx:1.14.2
    ports:
    - containerPort: 80