Blue green deployment is an application release model that gradually transfers user traffic from a previous version of an app or microservice to a nearly identical new release — both of which are running in production. 

A blue/green deployment is a deployment strategy in which you create two separate, but identical environments. One environment (blue) is running the current application version and one environment (green) is running the new application version.

The old version can be called the blue environment while the new version can be known as the green environment. Once production traffic is fully transferred from blue to green, blue can standby in case of rollback or pulled from production and updated to become the template upon which the next update is made.

Using a blue/green deployment strategy increases application availability and reduces deployment risk by simplifying the rollback process if a deployment fails. Once testing has been completed on the green environment, live application traffic is directed to the green environment and the blue environment is deprecated.

There are downsides to this continuous deployment model. Not all environments have the same uptime requirements or the resources to properly perform CI/CD processes like blue green. But many apps evolve to support such continuous delivery as the enterprises supporting them digitally transform.

Blue green deployment and Kubernetes

Kubernetes is a natural fit with all the elements associated with the blue green deployment process, including cloud-native apps, microservices, containers, continuous integration, continuous delivery, continuous deployment, SRE, and DevOps. As an open source platform that automates Linux® container operations, Kubernetes not only helps orchestrate the containers that package cloud-native apps’ microservices, but Kubernetes is also supported by a collection of architectural patterns that developers can reuse instead of creating application architectures from scratch.One of those Kubernetes patterns is known as the Declarative Deployment pattern. Since microservices are inherently small, they can multiply in number very quickly. The Declarative Deployment pattern reduces the manual effort needed to deploy new pods—the smallest and simplest unit in the Kubernetes architecture.