What are the common deployment strategies? What is the difference between Blue-Green and Canary deployments?

Four Main Deployment Strategies

Rolling Update Gradually replaces old version instances, updating one batch at a time.

• Pros: Low resource usage, no extra infrastructure needed
• Cons: Old and new versions coexist during transition; rollback is slower
• Best for: Routine updates to general web applications

Blue-Green Deployment Maintains two identical production environments (Blue=old, Green=new), then switches all traffic to the new environment at once.

• Pros: Instant switch, second-level rollback (just switch back to Blue)
• Cons: Resource costs double
• Best for: Critical systems requiring fast rollback capability

Canary Deployment Routes a small percentage of traffic (e.g., 5%) to the new version, then gradually increases the percentage as metrics look healthy.

• Pros: Lowest risk, limited blast radius if problems occur
• Cons: Longer deployment cycle, requires monitoring infrastructure
• Best for: High-traffic, high-risk feature updates

A/B Testing Similar to Canary, but the goal is comparing business metrics (conversion rate, click-through rate) between versions, not testing stability.

Comparison Summary

Strategy	Rollback Speed	Resource Cost	Risk
Rolling	Slow	Low	Medium
Blue-Green	Fast (seconds)	High (2x)	Low
Canary	Medium	Medium	Lowest