What is blue-green deployment?

Blue-green deployment is a software release strategy that reduces downtime risk and facilitates rollback. It involves having two identical environments: "blue" (current live version) and "green" (new version).

Process:

1. The new application version is deployed in the "green" environment.
2. All necessary tests are conducted in the "green" environment until it is fully ready.
3. Traffic is switched from "blue" to "green" environment. The switch occurs either instantly (e.g., via load balancer configuration change) or gradually.
4. The "blue" environment remains in reserve in case a rollback is needed or can be used for subsequent deployments.

Advantages:

• Minimal downtime: During the traffic switch, the old version continues to operate until the new one becomes primary.
• Easy rollback: If issues are found in the new version, traffic is instantly switched back to the "blue" environment.
• Deployment confidence: The new version is fully tested in a production-like environment before traffic switching.

Disadvantages:

• Infrastructure doubling: Requires two complete identical environments, which can be costly.
• State management: If the application has state (e.g., user sessions), it is necessary to consider how it will be handled during the switch.