🟦 Blue-Green Deployment

✅ Concept

Blue-Green deployment means you maintain two identical production environments:

Blue = Current Production
Green = New Version

Only one is active at a time.

✔ How it works

Deploy new application version to the Green environment.
Test it thoroughly (Smoke tests, automation, health checks).
Switch the traffic from Blue → Green (load balancer flip).
If something goes wrong:
- Switch traffic back to Blue (instant rollback).

🟢 Diagram (Simple Flow)

⭐ Advantages

Benefit	Description
Zero downtime deployment	Users don't see any interruption.
Instant rollback	One flip back to Blue.
Full environment testing	Green can be validated before traffic shift.

⚠️ Disadvantages

Issue	Explanation
Costly	Two full environments required.
Data sync complexity	DB schema changes require careful planning.

📌 When to Use Blue-Green

Releases require zero downtime.
System is stable, and deployments are less frequent.
Company can afford 2 parallel production environments.

🟧 Canary Deployment

✅ Concept

Canary deployment gradually releases the new version to a small subset of users first.

Like in coal mines, a "canary" tests the environment for problems.

✔ How it works

Deploy new version v2 to a small percentage (e.g., 1% of users).
Monitor behaviors (errors, CPU, logging, metrics).
Gradually increase traffic:

1% → 5% → 25% → 50% → 100%

If issues appear:

Stop rollout
Rollback to previous version

🟡 Diagram (Traffic Split)

⭐ Advantages

Benefit	Description
Very safe	Only a small portion sees new version first.
Real user testing	Validates with live traffic.
Fine-grained rollout control	You can stop at any time.

⚠️ Disadvantages

Issue	Description
More complex	Requires intelligent traffic routing & monitoring.
Harder to implement	Needs advanced infra (Istio, Envoy, Feature Flags).
Multiple versions live at once	Must manage compatibility.

📌 When to Use Canary Deployment

High-traffic applications.
Releases must be very cautious (e.g., banking/fintech).
Microservices environment.
Strong observability is in place (Prometheus, Grafana, ELK, AWS CloudWatch).

🆚 Blue-Green vs Canary — Quick Comparison

Feature	Blue-Green	Canary
Rollback	Instant	Gradual
Complexity	Low	High
Cost	High (2 environments)	Moderate
Risk Level	Medium	Very Low
Traffic Control	All users at once	Small → full rollout
Use Case	Enterprise apps, stable releases	Microservices, critical apps

🟩 Real-World Examples (Cloud & Kubernetes)

☁️ AWS Example

Blue-Green:

Using AWS Elastic Beanstalk, ALB switch, or CodeDeploy (blue/green).

Canary:

Using API Gateway Canary Release or App Mesh.

☸️ Kubernetes Example

Blue-Green:

Deploy new version as deployment-green, switch service selector.

Canary:

Using:

Istio VirtualService
Linkerd
Argo Rollouts
Flagger

Traffic can be:

5% to canary
95% to stable

🧠 Interview-Ready Summary

🟦 Blue-Green Deployment

➡ Two production environments.
➡ Switch traffic when new version is ready.
➡ Zero downtime + instant rollback.
➡ Easy but expensive.