Setting up a Virtual Private Cloud (VPC) in AWS can be a challenging task, especially if you encounter unexpected issues. In this post, I’ll share the problems I faced while configuring a VPC, along with the solutions that worked for me. As I'm still working on my VPC setup, I’ll continue to update this post with any new issues and resolutions I come across.

The approach in this blog is straightforward: I’ll first describe the problem and then provide the solution I used. Please note that while these solutions worked for me, there might be more efficient ways to resolve these issues.

Issue 1: Timeout When Communicating with DynamoDB or Other AWS Services from Lambda/EC2 after Setting Up a VPC Endpoint (Interface)

Problem:

After setting up a VPC Endpoint of type Interface, I encountered timeouts when my Lambda function or EC2 instance tried to communicate with DynamoDB or other AWS services.

Solution:

When you create an Interface-type VPC Endpoint, AWS provides a DNS name in its configuration. To ensure successful communication with DynamoDB or other AWS services, you need to use this DNS name in your code.

Additionally, double-check the security group (SG) rules:

• The outbound rule in your Lambda-linked security group should be configured to allow connections to AWS services via the endpoint.
• The security group linked with your VPC Endpoint must have an inbound rule that permits connections from the Lambda’s security group.

For more detailed steps, you can refer to my other blog post on creating and linking VPC Endpoints of type Interface.

Issue 2: Timeout When Connecting to Third-Party APIs Outside AWS (e.g., Stripe, Firebase)

Problem:

I experienced timeouts when trying to connect to third-party APIs, such as Stripe or Firebase, that are external to the AWS environment.

Solution:

This issue is often caused by misconfigured Network Address Translation (NAT) or Internet Gateway (IG) settings. Here’s what worked for me:

• Ensure the Internet Gateway is associated with the route table of the subnet designated as a public subnet.
• If your Lambda function or EC2 instance is in a private subnet and needs to connect to the public internet, configure a NAT. When setting up the NAT, make sure it’s associated with the public subnet where the Internet Gateway is linked. Then, associate the NAT with the route table of the private subnet.

For more details on setting up VPCs, check out these posts: Setting Up a VPC for Your App Using AWS Management Console and Setting Up a VPC and Lambda Function with Terraform.

Issue 3: Unable to Delete Subnets Linked to Lambda, Even After Detaching the VPC

Problem:

I wasn’t able to delete subnets linked to my Lambda function, even after detaching the VPC from Lambda.

Solution:

Before you can delete subnets, you need to remove any Network Interfaces (ENIs) associated with the Lambda function. However, in my case, the Network Interfaces were still marked as In-use despite detaching the VPC.

This was due to Lambda versioning. Even though I removed the VPC from the latest Lambda version, previous versions were still attached to the VPC. The solution was to delete the older Lambda versions, which then allowed me to remove the Network Interfaces and delete the subnets.

If you're facing similar issues, this GitHub repo was helpful for me. It contains a script that identifies what might be holding up your Network Interface. If the script doesn’t find any issues, consider contacting AWS support for further assistance.

Conclusion

Setting up a VPC in AWS can be tricky, but by understanding the common issues and how to resolve them, you can avoid a lot of frustration. Whether you're dealing with timeouts when connecting to services or issues with deleting resources, the solutions provided here should help you navigate these challenges.

I’ll continue updating this blog as I encounter new issues and find solutions, so be sure to check back for more insights!