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Run two copies of production and switch traffic between them for risk-free releases.
Quick Definition
Blue-green deployment is a release strategy that runs two identical environments, one live (blue), one staging the new version (green). Traffic switches to green once validated, enabling near-zero-downtime releases and instant rollback, though running parallel environments temporarily increases cost.
Blue-green deployment keeps two identical production environments. Blue serves users while green receives the new release. Once green is verified, traffic flips over instantly. If anything breaks, traffic flips back just as fast.
The reliability win is obvious: releases stop being scary. The cost angle is less discussed: you are paying for two production environments during the switchover. Disciplined teams keep that overlap short, or use ephemeral environments and autoscaling so the idle color shrinks when not in use.
Example. A payments team deploys on Friday afternoons without fear: the new version goes to green, automated checks run for 20 minutes, traffic flips, and blue stays warm for an hour as an instant rollback. Total extra cost: about one hour of duplicate capacity per release.
Blue-green pairs naturally with strong CI/CD. These CI/CD best practices cover how teams automate the whole flow.
Near-zero-downtime releases with an instant rollback path, since the previous version stays running until you retire it.
Briefly, double the production capacity. Keeping the overlap window short keeps the cost small.
Blue-green switches all traffic at once between two environments. Canary shifts a small percentage gradually to the new version.