Blue-green deployments

In blue-green deployments, the current version of the application service, called blue, handles all the application traffic. We then install the new version of the application service, called green, on the production system. The new service is not yet wired with the rest of the application.

Once green is installed, one can execute smoke tests against this new service and, if those succeed, the router can be configured to funnel all traffic that previously went to blue to the new service, green. The behavior of green is then observed closely and, if all success criteria are met, blue can be decommissioned. But if, for some reason, green shows some unexpected or unwanted behavior, the router can be reconfigured to return all traffic to blue. Green can then be removed and fixed, and a new blue-green deployment can be executed with the corrected version: