BlueGreen Deployment

The goal is to have zero-down time for deployment of the new version of the service. BlueGreen Deployment (BGD) is a technique having two instances (blue and green) of the same deployed service, and changing routing from one to another.

If newly enabled service (green) has bugs, you can rollback, change routing to the previous version of this service (blue).

There are multiple options of routing, which I'm omitting on purpose. What is more important to highlight is database state. You have two options how to make BGD and both have caveats.

Database per instance

This option can be used in the microservices when each service has its own database. In case you are using this option, you need to send POST requests to both services to maintain consistent state of databases.