A company needs to manage Amazon EC2 instances through command line interfaces for Linux hosts and Windows hosts. The EC2 instances are deployed in…

AWS Systems Manager Session Manager is designed to provide secure, auditable management of EC2 instances without needing inbound ports, bastion hosts, or SSH keys. By deploying VPC endpoints for Systems Manager, the SSM Agent on the instances can communicate with the Systems Manager service privately within the AWS network, satisfying the "no route to the internet" requirement. Session Manager integrates directly with AWS IAM, allowing for fine-grained, role-based access control to specific instances. This approach centralizes access control and eliminates the overhead of managing network infrastructure (like VPN/Direct Connect) or instance-level credentials, making it the solution with the least maintenance.

A. Setting up AWS Direct Connect is a high-overhead solution for dedicated network connectivity. It does not inherently provide the required role-based access control at the instance level without significant additional credential management.

C. An AWS Site-to-Site VPN introduces network management overhead and, like Direct Connect, only provides network-level access. It does not solve the need for granular, role-based instance access control without separate credential management.

D. Deploying a publicly accessible appliance (a bastion host) contradicts the "no route to the internet" constraint and introduces significant maintenance overhead for patching, securing, and managing the appliance itself.

1. AWS Systems Manager User Guide, "What is AWS Systems Manager Session Manager?": This document states, "Session Manager provides secure and auditable instance management without the need to open inbound ports, manage bastion hosts, or manage SSH keys... You can control which users can start sessions on which instances, and which commands they can run, by using AWS Identity and Access Management (IAM) policies."

2. AWS Systems Manager User Guide, "Step 2: Create VPC endpoints": This section details the procedure for using Session Manager in private subnets. It states, "If you're using a virtual private cloud (VPC) for your instances, you can optionally configure AWS PrivateLink to improve your security posture... By using AWS PrivateLink, you can connect to Systems Manager through a private endpoint in your VPC instead of connecting over the internet." This confirms its suitability for environments with no internet route.

3. AWS PrivateLink Developer Guide, "AWS services that integrate with AWS PrivateLink": This guide lists the service endpoints required for Systems Manager to function through VPC endpoints (ssm, ssmmessages, and ec2messages), confirming the technical feasibility of the solution in option B.

4. AWS Direct Connect User Guide, "What is AWS Direct Connect?": This document describes Direct Connect as a service to "establish a dedicated network connection from your premises to AWS." Its primary purpose is large-scale hybrid networking, making it overly complex and high-maintenance for the specific task of instance management.