EC2 - Access to internet is not working
Hi everyone. My 2 EC2 (Windows Server 2022) instances are not able to reach any destination on internet. I'm on east-2 region and the problem started with one of the instances; hours latter the second one got the same problem. I have apps that connects to remote databases, but the connections fail because the remote servers aren't reachable.
In other hand, I can connect to those apps from outside, so the problem is not with the incoming traffic. I've checked the VPC configuration, and nothing has changed since along time ago.
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- Make sure of the routing of the EC2 subnet route table, if the EC2 is in private subnet (has only private IP address) then make sure it has a default route to the NAT Gateway, or if the EC2 is in public subnet (has a public IP address) then make sure it has a default route to the Internet Gateway.
- Make sure of the security group and the ACLs are not blocking the traffic.
- If the above does not resolve the issue, then enable VPC flow logs and see how the traffic flow https://docs.aws.amazon.com/vpc/latest/userguide/working-with-flow-logs.html
The screenshot shows you can get in okay, is this directly by RDP over the internet to the public IP, or another method (e.g. bastion host, peered VPC, Direct Connect, or others)?
The route table for the subnet in which the Windows instance is provisioned would be the best place to start looking, extensive advice on how to troubleshoot and what to look out for is in https://repost.aws/knowledge-center/troubleshoot-vpc-route-table
As @Matt_E says, also check outbound security group rules, and if you're not getting anywhere then turn on VPC flow logs.
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