Which solution will meet these requirements?
Create a network ACL that blocks outbound traffic on port 80. Associate the network ACL with all subnets in the application account. In the application account and the core account, deploy one EC2 instance that runs a custom VPN server. Create a VPN tunnel to access the private VPC. Update the route table in the application account.
Create private VIFs for Systems Manager and Amazon S3. Delete the NAT gateway from the VPC in the application account. Create a transit gateway to access the patch source repository EC2 instances in the core account. Update the route table in the core account.
Create VPC endpoints for Systems Manager and Amazon S3. Delete the NAT gateway from the VPC in the application account. Create a VPC peering connection to access the patch source repository EC2 instances in the core account. Update the route tables in both accounts.
Create a network ACL that blocks inbound traffic on port 80. Associate the network ACL with all subnets in the application account. Create a transit gateway to access the patch source repository EC2 instances in the core account. Update the route tables in both accounts.
Explanations:
While creating a VPN server could provide connectivity, it does not effectively prevent all internet access or simplify the architecture. Using a NAT gateway is incompatible with the requirement to prevent all EC2 instances from accessing the internet. The solution is more complex and does not address connectivity to Systems Manager and S3.
Creating private VIFs is not necessary as AWS already provides VPC endpoints for Systems Manager and S3. Moreover, this option involves deleting the NAT gateway and setting up a transit gateway, which may be overly complicated and does not ensure that all EC2 instances are isolated from the internet.
This solution effectively addresses all requirements. By creating VPC endpoints for Systems Manager and Amazon S3, the EC2 instances can access these services without needing internet access. Additionally, a VPC peering connection allows access to the patch source repository in the core account, while ensuring that the NAT gateway is deleted, preventing any internet access.
Blocking inbound traffic on port 80 does not prevent outbound internet access and does not fulfill the requirement of preventing all EC2 instances from accessing the internet. A transit gateway could facilitate connectivity, but without the correct access methods to Systems Manager and S3, this option falls short of the requirements.
I opine that the answer is:
Create VPC endpoints for Systems Manager and Amazon S3. Delete the NAT gateway from the VPC in the application account. Create a VPC peering connection to access the patch source repository EC2 instances in the core account. Update the route tables in both accounts.