This content originally appeared on DEV Community and was authored by chatgptnexus
Network Address Translation (NAT) instances in AWS sometimes encounter connectivity issues when forwarding traffic from private EC2 instances. Here's a detailed analysis of common problems and their solutions.
Key Configuration Points
Source/Destination Check
- Disable source/destination checking on the NAT instance, as this is often the root cause of connectivity issues[3].
Network Configuration
- Ensure the private subnet's route table directs 0.0.0.0/0 traffic to the NAT instance
- The NAT instance must reside in a public subnet with proper routing to the Internet Gateway
Essential IPTables Configuration
# Enable IP forwarding
echo 1 > /proc/sys/net/ipv4/ip_forward
# Configure NAT rules
iptables -t nat -A POSTROUTING -o eth0 -s 10.0.0.0/16 -j MASQUERADE
iptables -A FORWARD -i eth0 -o eth1 -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT
Security Considerations
Security Group Settings
- NAT instance security group must permit inbound traffic from private subnets
- Allow all outbound traffic
- Private instance security groups need outbound rules to NAT instance[1]
Connection Timeout Issues
The NAT gateway terminates idle connections after 350 seconds. To prevent this:
- Implement TCP keepalive with values under 350 seconds
- Maintain active traffic flow over the connection[1]
Advanced Troubleshooting
Network Connectivity Tests
ping 8.8.8.8
traceroute 8.8.8.8
Consider using AWS NAT Gateway as an alternative for improved reliability and simplified management[1].
情報源
[1] Troubleshoot NAT gateways - Amazon Virtual Private Cloud https://docs.aws.amazon.com/vpc/latest/userguide/nat-gateway-troubleshooting.html
[2] NAT ゲートウェイのトラブルシューティング https://docs.aws.amazon.com/ja_jp/vpc/latest/userguide/nat-gateway-troubleshooting.html
[3] プライベートリソースが VPC の外側で通信できるようにする https://docs.aws.amazon.com/ja_jp/vpc/latest/userguide/work-with-nat-instances.html
[4] nat-instance(terraform-aws-nat-instance)を利用して発生した ... - Qiita https://qiita.com/fkdfkdfkd/items/09a15f32002dc44b6b18
This content originally appeared on DEV Community and was authored by chatgptnexus
chatgptnexus | Sciencx (2025-01-11T13:41:47+00:00) Troubleshooting AWS NAT Instance Connectivity Issues: A Comprehensive Guide. Retrieved from https://www.scien.cx/2025/01/11/troubleshooting-aws-nat-instance-connectivity-issues-a-comprehensive-guide/
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