The correct answer is B because when an IAM role is attached to an Amazon EC2 instance through an instance profile, changes to the permissions policy for that role propagate automatically to applications that use the instance role credentials. This is the least disruptive approach because the developer does not need to restart, hibernate, terminate, or replace the EC2 instance.

AWS documentation explains that applications running on EC2 can obtain temporary security credentials from the instance metadata service for the attached IAM role. When the IAM policy attached to that role is updated to allow Amazon S3 read access , new temporary credentials issued for the role will reflect the updated permissions. This makes it possible to correct the access issue without changing the application deployment model or interrupting the running instance.

Option A is unnecessary because terminating and relaunching the instance causes avoidable disruption. Option C is also unnecessary because hibernation and restart are not required for IAM policy changes to take effect. Option D is not the best answer because although bucket policies can grant access, the issue identified is specifically that the instance role lacks S3 read permission , and restarting the instance is still unnecessary.

The AWS best-practice approach is to grant the required permission directly to the IAM role used by the EC2 instance. This keeps authorization centralized and lets the running application continue using temporary role credentials with minimal operational impact.

Therefore, the solution with the least application disruption is to add the S3 read permission to the IAM role , making B the correct answer.