Blue-Green Deployment

Problem

Replacing production version 1 with version 2 directly creates a dangerous transition. If version 2 is broken, rollback may take time.

Solution — Blue-Green

Maintain two environments:
Blue  → v1 ← users
Green → v2 ← test
When Green is ready, switch traffic:
users → Green

To check Green with real users before sending everyone, a router that supports weighted traffic can send it 5% while Blue receives 95%. Increase Green's share after checking errors and response times. Blue-green describes the two separate environments; canary describes testing a release with a small share of production traffic before expanding it. You can combine both by using a canary rollout between Blue and Green.

Core idea: blue-green deployment makes release switching and rollback largely a traffic-routing decision.