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Docker vs Kubernetes (Production Reality)

1. Why This Guide Exists (The Real Confusion)

The Problem: "Should I use Docker or Kubernetes?" is a category error. It's like asking "Should I use a Brick or a House?" - You typically use both. - Docker is the Format (The Brick). - Kubernetes is the Orchestrator (The Architect & Construction Crew).

However, you can run Docker without Kubernetes (Docker Compose). This guide explains when to switch.

2. Mental Model (Antigravity View)

  • Docker Engine: Manual Transmission. You control every gear shift. Great for track days (Dev), tiring for detailed traffic (Prod).
  • Docker Compose: Cruise Control. Keeps slight order on one highway (Single Server).
  • Kubernetes: Self-Driving Traffic Network. Coordinates thousands of cars across a city, rerouting around accidents automatically.

3. Core Differences Table

Feature Docker Compose (Single Node) Kubernetes (Cluster)
Scope Single VM / Laptop Multiple VMs / Data Centers
Scaling Manual (docker-compose up --scale) Auto (HPA / Cluster Autoscaler)
High Availability None. If VM dies, App dies. High. Reschedules Pods to healthy nodes.
Load Balancing Simple (Round Robin DNS) Advanced (Ingress, Service Mesh)
Storage Host Volumes (Locked to VM) CSI (EBS/EFS moves with Pod)
Complexity Low (1 YAML file) High (Lots of YAML + Control Plane)
Cost Cheap (1 Server) Expensive (Control Plane + min 2 Nodes)

4. Production Architecture (Docker Compose)

Best For: MVPs, Admin Tools, Low-Traffic internal apps.

[ User ]
    |
[ Nginx Reverse Proxy (Container) ]
    | (Docker Internal Network)
    +---> [ App Container 1 ]
    |
    +---> [ App Container 2 ]
    |
[ Database Container ] (Volume mapped to Host /mnt/data)
The Failure Mode: If the EC2 instance has a hardware failure, your site is down until you manually spin up a new EC2 and run docker-compose up.

5. Production Architecture (Kubernetes)

Best For: Critical Business Apps, Microservices, 24/7 Availability.

[ User ] --> [ AWS ALB (Public) ]
                  |
         [ K8s Ingress Controller ]
                  |
    +-------------+-------------+
    |                           |
[ Node 1 ]                  [ Node 2 ]
(App Pod A)                 (App Pod B)
    |                           |
    +---> [ PostgreSQL RDS (External) ]
The Reliability Mode: 1. Node 1 catches fire. 2. K8s Control Plane detects "Node NotReady". 3. K8s schedules replacement Pod A onto Node 2. 4. Site remains up (Pod B handles traffic during switch).

6. The "Transition Point" (When to switch)

You are running Docker Compose on one big EC2. Switch to Kubernetes when: 1. Downtime is Unacceptable: You need Zero-Downtime deployments (Rolling Updates). Docker Compose restarts cause brief downtime. 2. Scale limit: Your traffic exceeds what the largest single EC2 (u-12tb1.112xlarge) can handle. 3. Team Size: You have > 5 developers pushing code daily. Coordinate "who updates the server" becomes a bottleneck. 4. Microservices: You split your monolith into 5+ services. Managing networking/discovery manually in Compose is painful.

7. Hybrid Patterns (The Middle Ground)

ECS (Elastic Container Service)

  • Mental Model: K8s "Lite".
  • Pros: Deep AWS integration, much simpler than K8s, reliable.
  • Cons: AWS Proprietary (Vendor Lock-in).

App Runner / Google Cloud Run

  • Mental Model: Serverless Containers.
  • Pros: "Here is my image, run it." Zero infrastructure.
  • Cons: Cold starts, less control over networking/caching.

8. Command Comparison

Action Docker Compose Kubernetes
Start docker-compose up -d kubectl apply -f folder/
Logs docker-compose logs -f kubectl logs -l app=backend -f
Shell docker-compose exec app bash kubectl exec -it pod-name -- bash
Scale docker-compose scale app=3 kubectl scale deploy/app --replicas=3
Delete docker-compose down kubectl delete -f folder/

9. Secrets Management Reality

  • Docker Compose: .env files. (Risk: Often checked into git accidental).
  • Kubernetes: Secrets API + External Secrets Operator (Syncs from AWS Secrets Manager). Much more secure/auditable.

10. Summary Recommendation

  1. Learning / Local Dev: Docker Compose. (K8s is too heavy for localhost unless using Minikube/Kind).
  2. Startups / MVPs: ECS / App Runner. (Save DevOps salary for features).
  3. Enterprise / Scale: EKS (Kubernetes). (Standardization, Ecosystem, Hiring pool).

Antigravity Rule: Do not use Kubernetes until you feel the pain of not having it. The "Pain of K8s" is high, so ensure the "Pain of Management" is higher.