Troubleshooting VPC Connectivity Issues with EC2 Instances

Answer - D.

All of the settings are right to ensure traffic can reach the external web server.

In the end, the issue could be at the web server end and it is blocking traffic.

Option A is incorrect since NAT gateways should be used for Instances in private subnets.

Option B is incorrect since the route table is already correct.

Option C is incorrect since not having a route to the NAT gateway would not cause the underlying issue.

For more information on Amazon VPC, one can visit the below URL.

https://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Introduction.html

Based on the provided information, the issue could be related to the routing of traffic. Let's analyze the details:

• An internet gateway is assigned to the VPC(10.0.0.0/16): This means that the VPC is properly connected to the internet and can send and receive traffic to/from the internet.

• The route table has a route for 0.0.0.0/0 to the Internet gateway: This route allows all traffic (0.0.0.0/0) to be directed to the internet gateway, which is the correct setup for internet connectivity.

• The Security Groups allow Outbound Traffic on port 443: The security groups are configured to allow outbound traffic on port 443, which means that the instances should be able to initiate connections to external servers on this port.

• The NACL allows Outbound Traffic on port 443 and Inbound Traffic for ephemeral ports: The network ACLs are configured to allow outbound traffic on port 443, and inbound traffic on ephemeral ports. This means that the instances should be able to establish connections to external servers on port 443, and receive responses on ephemeral ports.

Given the above details, we can conclude that the issue is not related to the VPC setup, but rather to the instances themselves or the external web server. Here are a few possibilities:

• The instances might have firewall rules that are blocking outbound traffic on port 443. To rule out this possibility, check the instance-level security groups and firewall configurations.

• The external web server might be blocking inbound traffic on port 443 from the VPC's IP address range. To rule out this possibility, check the web server's firewall or access control configurations.

In summary, the most likely cause of the issue is either firewall rules on the instances themselves or on the external web server. It is not related to the VPC setup or routing configurations.