Cannot connect p2p, issue with launchers that download games or other software.

Based on your description, it sounds like you're experiencing network connectivity issues with your Windows Server Core AMI instance, specifically with peer-to-peer (P2P) connections and game launchers.

Even though you've opened all inbound and outbound traffic in your security groups and disabled the Windows Firewall, there could be several other factors causing these connectivity issues:

1. Internet Gateway Configuration: Ensure your EC2 instance is in a public subnet with a properly attached Internet Gateway. Your instance needs a route to the Internet Gateway (0.0.0.0/0 → IGW) in its associated route table.

2. Public IP Address: Verify that your instance has a public IP address (either an Elastic IP or auto-assigned public IP). Without a public IP, external services cannot establish connections to your instance.

3. Network ACLs: Check your Network Access Control Lists (NACLs) to ensure they're not blocking the required traffic. Even if security groups are open, restrictive NACLs could block connections.

4. DNS Configuration: Ensure DNS hostnames and DNS resolution are enabled for your VPC. This is crucial for proper name resolution.

5. NAT Requirements: Some game launchers and P2P applications may require specific NAT configurations that aren't fully supported in the AWS environment.

6. MTU Settings: Maximum Transmission Unit misconfigurations can sometimes cause issues with certain types of traffic, particularly P2P connections.

7. Application-Level Restrictions: Some applications may have built-in restrictions when running on server operating systems or detect virtualized environments.

To troubleshoot:

• Try using basic network diagnostic tools like ping, traceroute, and nslookup to verify basic connectivity
• Check if you can access websites using curl or a browser
• Verify your route table configuration with ip route command
• Consider using AWS's VPC Reachability Analyzer to diagnose network path issues
• Try a different instance type or AMI to see if the issue persists

If these steps don't resolve your issue, you might need to contact AWS Support for more in-depth troubleshooting, as there could be specific limitations with running game launchers on Windows Server Core in AWS.
Sources
Internet outbound problem | AWS re:Post
EC2 Instances in the us-east-1 and us-east-2 region can ping outside but not able to curl/wget/telnet | AWS re:Post