Amazon Web Services (AWS) offers various serverless solutions and among them, AWS Lambda is the most prominent one. It allows developers to run their code without worrying about provisioning or managing servers. Lambda works in close relation with the AWS ecosystem, including Virtual Private Cloud (VPC), which offers isolated and secure environments for resources in the AWS cloud. In this article, we will cover how to access private resources in VPCs from Lambda code. This an important topic to grasp for the AWS Certified Developer – Associate (DVA-C02) examination.

Table of Contents

Understanding AWS Lambda

AWS Lambda provides an execution environment for your code, called a “Lambda function”. Within this environment, your code runs in stateless compute containers that are automatically provisioned for you. The best part? You only pay for the compute time that you use – you are not charged when your code is not running.

Understanding AWS VPC

AWS VPC offers a logically isolated part of the AWS cloud where you can launch resources within a defined virtual network which you have complete control over. VPC configurations allow you to manage your own IP address range, subnets, route tables, and network gateways to provide a tailored networking environment.

Accessing Private Resources in VPCs from Lambda

To access resources that are inside a VPC, you need to configure your Lambda function to access the VPC. AWS offers several ways to access your VPC resources from your Lambda function, which include the Elastic Network Interface (ENI) and AWS PrivateLink.

Elastic Network Interface (ENI):

When you add VPC configuration to your Lambda function, it creates an Elastic Network Interface (ENI) in your VPC and uses that network interface to connect to resources in your VPC. The Lambda function received returned responses from the VPC through the same network interface.

const AWS = require('aws-sdk');
const docClient = new AWS.DynamoDB.DocumentClient();

exports.handler = async (event) => {
let params = {
TableName : 'yourdynamodbtable',
Key: { 'ID' : }

let item = '';
let data = await docClient.get(params).promise()
.then((response) => {
item = response.Item;
.catch((err) => console.error(err));

return item;

AWS PrivateLink:

Alternatively, you can use AWS PrivateLink to access services over AWS PrivateLink from your Lambda function. AWS PrivateLink is a highly available, scalable technology that enables you to privately connect your VPC to supported AWS services, services hosted by other AWS accounts, and supported AWS Marketplace services.

Method of Access Elastic Network Interface (ENI) AWS PrivateLink
Connection to VPC Directly through ENI Via VPC endpoint
Security Inherently secure More secure as traffic does not leave AWS network
Scalability Limited by size of subnet Highly scalable
Availability High Higher than ENI
Inter-region support No Yes

In conclusion, AWS Lambda and VPCs work hand-in-hand to enable serverless applications to securely and efficiently communicate with private resources. Understanding the intricacies of accessing private resources in VPC’s from lambda code is a crucial part of mastering AWS, particularly in preparation for the AWS Certified Developer – Associate (DVA-C02) examination. As with any AWS service, it’s essential to refer to the official AWS documentation and follow best practices for security and efficiency.

Practice Test

True/False: AWS Lambda is able to access resources within your VPC by default.

  • False

Answer: False

Explanation: AWS Lambda functions are not able to access resources within your VPC by default. You need to explicitly set the VPC access for the Lambda functions.

Multiple Select: What can be done to give AWS Lambda access to private resources in a VPC?

  • A. Assign IAM roles
  • B. Use security groups
  • C. Create a NAT gateway
  • D. Specify subnets and security groups

Answer: A, B, D

Explanation: IAM roles, security groups and specifying subnets can provide Lambda access to private resources in VPC. Creating a NAT gateway is not directly related to granting Lambda access to resources in a VPC.

True/False: When a Lambda function is configured to access resources within a VPC, it doesn’t lose its internet access.

  • False

Answer: False

Explanation: When a Lambda function is configured to access resources within a VPC, it does lose its internet access unless a NAT gateway is configured.

Single Select: Which AWS service can be used by AWS Lambda to securely access resources inside a VPC?

  • A. Amazon RDS
  • B. Amazon S3
  • C. AWS PrivateLink
  • D. Amazon EC2

Answer: C. AWS PrivateLink

Explanation: AWS PrivateLink enables the private connectivity between VPCs, AWS services, and on-premises applications, all on the same network.

True/False: It is mandatory to use AWS PrivateLink to allow Lambda functions to access resources inside a VPC.

  • False

Answer: False

Explanation: While AWS PrivateLink can provide secure access to resources in a VPC, it is not the only way and hence, not mandatory.

Multiple Select: Which of the following will restrict Lambda’s access to resources within a VPC?

  • A. Limited security group access
  • B. Insufficient IAM permissions
  • C. Connected to public subnets only
  • D. Not connected to an ElastiCache cluster

Answer: A, B, C

Explanation: Limited security group settings, Insufficient IAM permissions and connection to public subnets only can restrict Lambda’s access to resources within a VPC. Connection status with ElastiCache cluster does not influence this access rule.

True/False: AWS Lambda requires an Elastic IP address attached to a NAT gateway to communicate with a private resource in a VPC.

  • True

Answer: True

Explanation: To communicate with a private API inside your VPC, your Lambda function communicates with your NAT gateway over the internet. The NAT gateway must have an associated Elastic IP address.

Single Select: What type of AWS Lambda function access needs NAT or VPC endpoint configuration?

  • A. Access resources over internet
  • B. Access resources in a VPC
  • C. Access resources in a public subnet
  • D. Access resources in other AWS accounts

Answer: B. Access resources in a VPC

Explanation: When AWS Lambda function is set up to access resources inside a VPC, it requires NAT or VPC endpoint configuration.

True/False: When a Lambda function is associated with a VPC, it incurs additional charges.

  • True

Answer: True

Explanation: Network data transfer costs apply when a Lambda function accesses resources across VPCs or VPC peering connections.

Multiple Select: Which of the following are needed to give access to AWS Lambda functions to access resources in a VPC?

  • A. VPC ID
  • B. Subnet IDs
  • C. Security group IDs
  • D. Lambda function ID

Answer: A, B, C

Explanation: To create a VPC-enabled Lambda function, you need to specify the VPC ID, Subnet IDs and Security Group IDs. Lambda function ID is not required.

Interview Questions

What is a VPC in the context of AWS?

Virtual Private Cloud (VPC) is a virtual network dedicated to your AWS account. It is logically isolated from other virtual networks in the AWS cloud, providing you a secure environment to launch your resources.

What is AWS Lambda?

AWS Lambda is a serverless compute service that lets you run your code without provisioning or managing servers. AWS Lambda executes your code only when needed and scales automatically.

How can you connect a Lambda function to an Amazon VPC?

You can configure your Lambda function to access resources within your VPC by providing subnet IDs and security group IDs during the Lambda creation process.

Can an AWS Lambda function in one VPC access resources in another VPC?

Yes, a Lambda function can access resources in another VPC using VPC peering, but the function will require appropriate permissions.

Are there additional charges for running a Lambda function inside a VPC?

You are not charged extra for running a Lambda function in a VPC. However, standard data transfer charges might be applicable based on your usage.

Do you have to modify your security groups to allow AWS Lambda to access resources in your private VPC?

Yes, you need to set up your security groups to allow AWS Lambda to access your resources within your VPC.

How does AWS Lambda gain access to a VPC?

AWS Lambda establishes an elastic network interface in one of the subnets of the VPC you specify, which enables the Lambda function to connect to your VPC resources.

How does AWS Lambda connect to resources in a private subnet?

AWS Lambda uses ENIs (Elastic Network Interfaces) that it sets up in the VPC to connect to resources in a private subnet.

Can you connect a Lambda function to a VPC in a different AWS account?

No, a Lambda function can be connected only to the VPC in the same AWS account.

What happens if the associated VPC of a Lambda function is deleted?

If the VPC is deleted, the Lambda function that depends on it will not be able to execute successfully unless it is reconfigured.

Are there any restrictions in using Amazon S3 with VPC?

You cannot directly access Amazon S3 from within a VPC. You must set up an Internet Gateway in your VPC or use VPC endpoints to connect.

Is it possible to use both VPC and non-VPC resources in the same lambda function?

Yes, it is possible for a Lambda function to access both VPC and non-VPC resources. However, you must configure an Internet Gateway for your VPC in order for the Lambda function to access non-VPC resources.

Can I modify my Lambda function’s VPC settings after it was created?

Yes, you can modify the VPC settings, including the attached subnets and security groups of your Lambda function, after it has been created.

Can a Lambda function in a VPC access the internet?

Yes, but only if the VPC has a configured Internet Gateway and the Lambda function’s security group rules allow outbound internet access.

What are the benefits of running a Lambda function inside a VPC?

Executing a Lambda function within a VPC allows it to access resources within the same VPC, apply security groups and network ACLs to function, and connect to a private endpoint, among other benefits.

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