Blue-green deployment is a deployment strategy that utilizes two identical environments, a “blue” (aka staging) and a “green” (aka production) environment with different versions of an application or service. Quality assurance and user acceptance testing are typically done within the blue environment that hosts new versions or changes. User traffic is shifted from the green environment to the blue environment once new changes have been testing and accepted within the blue environment. You can then switch to the new environment once the deployment is successful.

Blue-Green vs Canary Deployment Strategies: The Blue-Green Deployment

Pros:

One of the benefits of the blue-green deployment is that it is simple, fast, well-understood, and easy to implement. Rollback is also straightforward, because you can simply flip traffic back to the old environment in case of any issues. Blue-green deployments are therefore not as risky compared to other deployment strategies.

Cons:

Cost is a drawback to blue-green deployments. Replicating a production environment can be complex and expensive, especially when working with microservices. Quality assurance and user acceptance testing may not identify all of the anomalies or regressions either, and so shifting all user traffic at once can present risks. An outage or issue could also have a wide-scale business impact before a rollback is triggered, and depending on the implementation, in-flight user transactions may be lost when the shift in traffic is made. 

https://www.harness.io/blog/blue-green-canary-deployment-strategies