Answer - B and C.
This is mentioned in an AWS whitepaper.
You can shift traffic all at once, or you can do a weighted distribution.
With Amazon Route 53, you can define a percentage of traffic to go to the green environment and gradually update the weights until the green environment carries the full production traffic.
A weighted distribution provides the ability to perform canary analysis where a small percentage of production traffic is introduced to a new environment.
It also allows the green environment to scale out to support the full production load if you're using Elastic Load Balancing, for example.
Elastic Load Balancing automatically scales its request-handling capacity to meet the inbound application traffic.
Option A is invalid since this is used for failover purposes.
Option D is invalid since you should not deploy your applications using just a single AZ.
For more information on Blue Green deployments, please refer to the below URL-
https://d1.awsstatic.com/whitepapers/AWS_Blue_Green_Deployments.pdf
Blue Green Deployment is a technique used for deploying applications in a way that reduces downtime, risk and provides a more seamless deployment experience. It involves creating two identical environments (Blue and Green) and directing traffic between them through a load balancer. Once the new version of the application is tested and validated in the Green environment, traffic is switched from the Blue environment to the Green environment, and the Blue environment is retired.
Here are the options that can help you achieve Blue Green deployments:
A. Use Route 53 with the failover routing policy: Route 53 is a DNS (Domain Name System) service provided by AWS that can be used to direct traffic between two identical environments (Blue and Green) using failover routing policy. This policy is used to direct traffic to a healthy environment (Blue or Green) and automatically switch traffic to a secondary environment if the primary environment fails. Failover routing policy works best when the primary and secondary environments are in different Availability Zones (AZs) to ensure high availability.
B. Use Route 53 with the weighted routing policy: Route 53 can also be used to direct traffic between two identical environments (Blue and Green) using the weighted routing policy. In this policy, traffic is distributed between the two environments based on a specified weight. During a Blue Green deployment, the Green environment can be given a higher weight, and as the application is validated in the Green environment, the weight can be gradually increased, and the Blue environment can be eventually retired.
C. Ensure that the application is placed behind an ELB: An Elastic Load Balancer (ELB) is a service provided by AWS that can be used to distribute traffic across multiple instances of an application deployed in different Availability Zones. ELB can be used to direct traffic between two identical environments (Blue and Green) during a Blue Green deployment. Once the new version of the application is validated in the Green environment, traffic can be directed to the Green environment through ELB, and the Blue environment can be retired.
D. Ensure that the application is placed in a single AZ: Placing the application in a single Availability Zone (AZ) is not recommended as it increases the risk of downtime due to single point of failure. In a Blue Green deployment, it is recommended to place the Blue and Green environments in different AZs to ensure high availability and reduce the risk of downtime.
In conclusion, options A and B can help achieve Blue Green deployments using Route 53 with failover routing policy and weighted routing policy, respectively. Option C using ELB is also a viable solution, while option D is not recommended as it increases the risk of downtime.
