Your application is currently hosted in an Elastic Beanstalk environment. Configuration changes need to be made to the environment. You have been told that the changes should not affect the current environment since downtime needs to be minimized. The code needs to be deployed only to the new instances. Which of the following Elastic Deployment mechanisms would you consider using?

Answer options:

A.All at Once
B.Rolling
C.Rolling with Additional Batch
D.Immutable

Answer - D
The AWS Documentation mentions the following.
Immutable updates are an alternative to rolling updates where a temporary Auto Scaling group is launched outside of your environment with a separate set of instances running on the new configuration, which are placed behind your environment`s load balancer. Old and new instances both serve traffic until the new instances pass health checks. The new instances are then moved into your environment`s Auto Scaling group and the temporary group and old instances are terminated.
All other options are invalid since it clearly mentions that the current environment should not be changed.
For more information on updating environments, please refer to the below URL
https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/environments-updating.html
Note:
Rolling updates have downtime. However, it is not for the entire infrastructure. It will be divided into batches. 
AWS Docs says that "When a configuration change requires instances to be replaced, Elastic Beanstalk can perform the update in batches to avoid downtime while the change is propagated. During a rolling update, capacity is only reduced by a single batch size, which you can configure. Elastic Beanstalk takes one batch of instances out of service, terminates them, and then launches a batch with the new configuration. After the new batch starts serving requests, Elastic Beanstalk moves on to the next batch."