The answer for the question is - Option D (Change the resource record weight to 0)
Reason:- Let’s break the question into parts to get to the answer.
Blue-Green Deployments - this is a technique that reduces downtime and risk by running two identical production environments called Blue & Green.
At any time, only one of the environments is live, with the live environment serving all production traffic. Here, we can consider Blue as live environment.
As you prepare a new version of your software, deployment and the final state of testing takes place in the environment that is not live (Here its Green ). Once you have deployed and fully tested the software in Green, you switch the router so all incoming requests now go to Green instead of Blue. Green is now live, and Blue is idle.
This technique can eliminate downtime due to application deployment. In addition, Blue-Green deployment reduces risk: if something unexpected happens with your new version on Green, you can immediately roll back the last version by switching back to Blue.
80%-20% setup is already done - this means the customer has implemented Weighted Routing Policy.
Weighted Routing Policy - this is used to route traffic to multiple resources in proportions that you specify with a single domain or subdomain name.
In our question it’s mentioned as 80-20 weighted routing is set, and we can consider 80% is Blue (Production), and 20% is Green (New Version).
Now the new deployment is done, and the customer wants to send the complete traffic to the updated one i.e., the current 80%-20% needs to be made to 100% only. To do this, the resource which is having older version ‘weight’ should be assigned ‘0’. Once this value is given, the traffic will not be going to this server.