AWS Lambda VPC access configuration allows your Lambda functions to access resources within a Virtual Private Cloud (VPC), such as Amazon RDS databases, ElastiCache clusters, or internal APIs that are not exposed to the public internet.
When you configure a Lambda function for VPC access, you must…AWS Lambda VPC access configuration allows your Lambda functions to access resources within a Virtual Private Cloud (VPC), such as Amazon RDS databases, ElastiCache clusters, or internal APIs that are not exposed to the public internet.
When you configure a Lambda function for VPC access, you must specify the following:
1. **VPC ID**: The Virtual Private Cloud where your resources reside.
2. **Subnets**: You should select at least two subnets in different Availability Zones for high availability. Lambda creates Elastic Network Interfaces (ENIs) in these subnets to connect to your VPC resources.
3. **Security Groups**: These control inbound and outbound traffic for your Lambda function within the VPC. The security groups must allow traffic to your target resources.
**Key Considerations:**
- **Internet Access**: When Lambda is configured for VPC access, it loses default internet connectivity. To enable internet access, you must place your function in private subnets with a route to a NAT Gateway or NAT Instance in a public subnet.
- **AWS Service Access**: To access AWS services like DynamoDB or S3 from a VPC-enabled Lambda, use VPC Endpoints (PrivateLink) or route traffic through a NAT Gateway.
- **IAM Permissions**: The Lambda execution role requires permissions including ec2:CreateNetworkInterface, ec2:DescribeNetworkInterfaces, and ec2:DeleteNetworkInterface.
- **Cold Start Impact**: VPC-configured functions previously experienced longer cold starts, but AWS introduced Hyperplane ENIs which significantly reduced this latency.
- **IP Addresses**: Lambda functions use private IP addresses from the specified subnets. Ensure sufficient IP addresses are available in your subnets.
**Best Practices:**
- Use dedicated subnets for Lambda functions
- Configure multiple subnets across AZs
- Plan your CIDR blocks to accommodate ENI requirements
- Implement VPC Endpoints for AWS service access when possible
This configuration is essential for building secure, enterprise-grade serverless applications that need to interact with private resources.
Lambda VPC Access Configuration
Why It Is Important
AWS Lambda functions by default run in an AWS-managed VPC with internet access. However, many enterprise applications require Lambda to access resources inside a private VPC, such as RDS databases, ElastiCache clusters, or internal APIs. Understanding VPC access configuration is crucial for the AWS Developer Associate exam and real-world scenarios where security and network isolation are paramount.
What Is Lambda VPC Access Configuration?
Lambda VPC access configuration allows your Lambda function to connect to resources within your Amazon Virtual Private Cloud. When configured, Lambda creates Elastic Network Interfaces (ENIs) in the subnets you specify, enabling the function to communicate with private resources like databases, internal services, and other VPC-bound components.
Key Components: • VPC ID - The Virtual Private Cloud where your resources reside • Subnet IDs - Private subnets where Lambda creates ENIs (recommend multiple for high availability) • Security Group IDs - Controls inbound and outbound traffic for the Lambda function
How It Works
1. ENI Creation: When you configure VPC access, Lambda uses AWS Hyperplane to create shared ENIs in your specified subnets. These ENIs are managed by Lambda and shared across function invocations.
2. IP Address Assignment: Each ENI receives a private IP address from your subnet's CIDR range. Ensure your subnets have sufficient available IP addresses.
3. Network Path: Traffic from Lambda to VPC resources flows through these ENIs. The function assumes the network identity defined by the associated security groups.
4. Internet Access Consideration: A VPC-enabled Lambda function loses default internet access. To restore it, you must: • Place Lambda in private subnets • Configure a NAT Gateway or NAT Instance in a public subnet • Update route tables to direct internet-bound traffic through the NAT
Required IAM Permissions
The Lambda execution role needs these permissions: • ec2:CreateNetworkInterface • ec2:DescribeNetworkInterfaces • ec2:DeleteNetworkInterface • ec2:AssignPrivateIpAddresses • ec2:UnassignPrivateIpAddresses
The managed policy AWSLambdaVPCAccessExecutionRole includes these permissions.
Cold Start Considerations
VPC-enabled Lambda functions previously had longer cold starts due to ENI provisioning. AWS Hyperplane improvements have significantly reduced this, but understanding the architecture remains important for exam questions.
Exam Tips: Answering Questions on Lambda VPC Access Configuration
• Private Subnet Placement: When a question asks about Lambda accessing private RDS or ElastiCache, the answer involves configuring VPC access with private subnets.
• Internet Access Pattern: If a VPC-enabled Lambda needs to call external APIs or AWS services, look for answers mentioning NAT Gateway in public subnets or VPC Endpoints.
• Security Groups: Remember that Lambda uses security group outbound rules to reach resources, and target resources use inbound rules to accept Lambda traffic.
• IP Exhaustion: Questions about Lambda failures in VPC often relate to insufficient IP addresses in subnets. Solution: use larger subnets or multiple subnets.
• IAM vs VPC: Distinguish between IAM permissions (for AWS API calls) and VPC configuration (for network-level access to resources).
• Multiple Subnets: For high availability, configure Lambda with subnets in multiple Availability Zones.
• VPC Endpoints: For accessing AWS services like DynamoDB or S3 from VPC-enabled Lambda, VPC Endpoints provide private connectivity and are a common exam topic.
• Troubleshooting Pattern: If Lambda times out connecting to VPC resources, check security groups, NACLs, and route tables.