Can you explain the concept of Blue–green deployment and how it is used to update systems without downtime?

Blue–green deployment is a deployment strategy where there are two identical environments: "blue" (the current live environment) and "green" (the new version of the application). The new version is deployed in the green environment, and after successful testing, traffic is switched from blue to green.

Advantages:

• The update occurs without downtime, as users always work with one of the two environments.
• Fast rollback: if issues are found in the new version, traffic can be quickly switched back to the blue environment.

Implementation:

1. Deploy the new version of the application in the green environment.
2. Conduct testing and verify functionality.
3. Switch the load balancer or DNS so that users start accessing the green environment.
4. The blue environment remains as a backup in case of rollback.

Thus, blue-green deployment minimizes risks and ensures system continuity during updates.