Serverless AWS Lambda Development · Lesson

Network Security Best Practices

Implement robust network security for Lambda functions in a VPC using security groups, network ACLs, and private endpoints to minimize attack surface.

Network Security Best Practices is a free Serverless AWS Lambda Development lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Serverless AWS Lambda Development learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Secure Lambda in a VPC

When your AWS Lambda function operates within a Virtual Private Cloud (VPC), it gains access to private resources like databases. This also means you need to secure its network communication.

Network security is critical to prevent unauthorized access and data breaches for your serverless applications.

Security Groups Explained

Security Groups (SGs) act as virtual firewalls for your Lambda's network interfaces within a VPC.

They control inbound and outbound traffic at the instance (ENI) level.
SGs are stateful: if you allow outbound traffic, the return inbound traffic is automatically allowed.
You attach SGs directly to your Lambda function's ENIs when it's configured in a VPC.

SG Rules: Least Privilege

When setting up Security Group rules, always follow the principle of least privilege.

Inbound Rules: Specify which traffic is allowed into your Lambda (e.g., from a database).
Outbound Rules: Specify which traffic your Lambda is allowed to send out (e.g., to S3 or a database).

Only open ports and allow traffic from trusted sources or to necessary destinations.

Network ACLs (NACLs)

Network Access Control Lists (NACLs) provide an additional layer of security at the subnet level within your VPC.

NACLs are stateless: you must explicitly allow both inbound and outbound return traffic.
They can include both allow and deny rules, processed in order by rule number.
NACLs apply to all resources within a subnet, including your Lambda's ENIs.

SG vs. NACL Comparison

Both Security Groups and NACLs filter network traffic, but they operate at different levels:

Security Groups: Instance-level (ENI), stateful, allow rules only.
NACLs: Subnet-level, stateless, allow & deny rules, processed by rule number.

Typically, you use SGs for granular control over specific resources and NACLs as a broader, coarser security layer for subnets.

Accessing AWS Services Privately

When your Lambda function is in a VPC, its traffic to public AWS services (like S3, DynamoDB, CloudWatch) would normally exit the VPC via a NAT Gateway or Internet Gateway.

This can introduce security risks and extra costs. VPC Endpoints allow private, secure communication to these services within your VPC.

Interface Endpoints Explained

Interface Endpoints (powered by AWS PrivateLink) provide a private connection to services using an Elastic Network Interface (ENI) in your VPC.

They allow your Lambda to access services like S3, DynamoDB, and CloudWatch Logs without traversing the public internet.
Traffic stays entirely within the AWS network, enhancing security and potentially reducing latency.

Endpoint Security

VPC Endpoints themselves can be secured:

Endpoint Policies: You can attach IAM resource policies directly to an endpoint to control which principals can use it and what actions they can perform.
Security Groups: For Interface Endpoints, you can associate a Security Group with the endpoint's ENIs. This SG controls traffic to and from the endpoint.

This ensures only authorized Lambda functions or resources can use the private connection.

Secure S3 Access Scenario

Imagine a Lambda function in a VPC that needs to upload files to an S3 bucket.

To do this securely and privately, you would:

Configure the Lambda in a private subnet with specific Security Group rules.
Set up an S3 Interface Endpoint in your VPC.
Apply an Endpoint Policy to the S3 Endpoint and attach a Security Group to its ENIs.

This ensures S3 traffic never leaves the AWS private network.

Lambda S3 Interaction

This Python Lambda function uploads a simple text file to an S3 bucket. When deployed within a VPC, its network access to S3 would be governed by the Security Groups, Network ACLs, and VPC S3 Endpoint configured in your VPC.

import boto3
import os

def lambda_handler(event, context):
    s3_client = boto3.client('s3')
    bucket_name = os.environ.get('BUCKET_NAME', 'your-secure-bucket-name')
    file_content = "Hello from a secure Lambda!"
    file_name = "secure_lambda_output.txt"

    try:
        s3_client.put_object(Bucket=bucket_name, Key=file_name, Body=file_content)
        return {
            'statusCode': 200,
            'body': f'Successfully uploaded {file_name} to {bucket_name}'
        }
    except Exception as e:
        print(f"Error uploading to S3: {e}")
        return {
            'statusCode': 500,
            'body': f'Failed to upload to S3: {str(e)}'
        }

Network Security Check

Which of the following statements about network security for Lambda functions in a VPC are TRUE?

Recap & Best Practices

You've learned how to secure your Lambda functions within a VPC!

Security Groups offer stateful, instance-level traffic control.
Network ACLs provide stateless, subnet-level filtering.
VPC Endpoints enable private access to other AWS services like S3 and DynamoDB.

Always apply the principle of least privilege to minimize your attack surface and keep your serverless applications secure.

Frequently asked questions

Is the “Network Security Best Practices” lesson free?

Yes — the full text of “Network Security Best Practices” is free to read here on the web, and the Serverless AWS Lambda Development course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Serverless AWS Lambda Development course, upgrade to CoddyKit PRO.

What will I learn in “Network Security Best Practices”?

Implement robust network security for Lambda functions in a VPC using security groups, network ACLs, and private endpoints to minimize attack surface. You practise Serverless AWS Lambda Development with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Serverless AWS Lambda Development?

No prior experience is required. Serverless AWS Lambda Development on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Network Security Best Practices” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Serverless AWS Lambda Development lesson?

Yes. Every Serverless AWS Lambda Development lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

Lambda in a VPC for Private Resources
Accessing Databases in VPC
Network Security Best Practices
NAT Gateways and Internet Access from a VPC

← Back to Serverless AWS Lambda Development