For more details see the Knowledge Center article with this video: https://aws.amazon.com/premiumsupport/knowledge-center/ec2-systems-manager-vpc-endpoints/ Amrutha shows you how to create VPC endpoints so that you can use Systems Manager to manage private EC2 instances without internet access.
Configure Amazon EC2 Instances at Scale by Executing Chef Recipes with AWS Systems Manager
How do I use AWS Systems Manager to join a new instance to my AWS Directory Service domain?
AWS re:Invent 2018: [REPEAT 1] Managing Modern Infrastructure in Enterprises (ENT227-R1)
AWS re:Invent 2017: Use Amazon EC2 Systems Manager to Perform Automated Resilience T (DEV338)
AWS re:Invent 2017: GPS: Too Many Tools? Amazon EC2 Systems Manager Bridges Operatio (GPSTEC307)