How do I troubleshoot timeout issues with a Lambda function that's in an Amazon VPC?

Resolution

Confirm that there's a valid network path to the endpoint that your function is trying to reach. To review your network settings, see How do I give internet access to a Lambda function that's connected to an Amazon VPC?

Important: If you're using a custom Dynamic Host Configuration Protocol (DHCP) options set, then confirm that your custom DNS server is working as expected.

Configure the following network settings:

• Route tables
• Subnets
• Security groups
• Network access control lists (network ACLs)
  Note: Security groups require outbound rules only for Lambda. Network ACLs require both inbound and outbound rules for Lambda.
• DNS hostnames and DNS resolution
• NAT and virtual private cloud (VPC) endpoints
  Note: Internet access from a private subnet requires NAT. To give internet access to an VPC-connected Lambda function, route the outbound traffic to a NAT gateway or NAT instance in a public subnet.

If you're using an AWS SDK, then check if the SDK provides any error logs that can help you determine what's causing the timeouts.

Related information

How do I troubleshoot issues with Amazon VPC route tables?

How does DNS work and how do I troubleshoot partial or intermittent DNS failures?

How do I troubleshoot connectivity issues between an interface Amazon VPC endpoint and an endpoint service?

Troubleshoot networking issues in Lambda