Can you explain the concept and working principle of Blue-Green deployment?

Blue-Green deployment is an application update strategy that minimizes downtime and risks when releasing a new version.

The idea is that you have two identical environments (Blue and Green). One of them is active and serving users (for example, Blue), while the other (Green) is prepared with the new version of the application. After testing the new version in Green, traffic is switched from Blue to Green. If something goes wrong, you can quickly roll back by switching traffic back to Blue.

Example:

• Blue — current live version
• Green — new version

Advantages:

• Minimal downtime
• Quick rollback
• Ability to test in a real environment without affecting users

In Node.js, this can be implemented through a load balancer that directs traffic to the appropriate environment.