EC2 Instance Connect Endpoint is the correct answer because it allows secure SSH access to private EC2 instances without public IP addresses, bastion hosts, NAT gateways, or inbound internet access. This directly satisfies the company’s restrictions and supports cost reduction by allowing the NAT gateways to be decommissioned if they are only used for this troubleshooting access pattern. Session Manager is not valid because the company does not support installing agents, and Session Manager requires the SSM Agent and Systems Manager connectivity. Bastion hosts require additional EC2 infrastructure and inbound access controls. Client VPN adds VPN management and does not remove the need for routing design across all VPCs as cleanly as EC2 Instance Connect Endpoint.