Introduction: Secure File Transfers with AWS Transfer Family
In an era where data is the lifeblood of business, securely and efficiently exchanging files with external partners, customers, and systems is not just a technical requirement—it’s a critical business function. With over 90% of organizations using the cloud1, traditional, self-managed Secure File Transfer Protocol (SFTP) servers are increasingly being replaced by managed, cloud-native solutions. AWS Transfer Family offers a powerful platform to modernize these workflows, providing a fully managed service for file transfers into and out of Amazon S3 or Amazon EFS.
HWS helps organizations unlock the full potential of AWS Transfer Family, offering end-to-end support for design, deployment, and optimization of secure file transfer workflows. Whether you’re migrating from legacy systems or building a new solution from scratch, HWS ensures a seamless transition with minimal disruption and maximum efficiency.
The Challenge of secure External File Exchange
Organizations often struggle with the operational overhead of traditional SFTP servers. This includes patching operating systems, managing server uptime, scaling for performance, and ensuring a strong security posture against constant threats. Self-managed solutions can become costly bottlenecks, demanding significant time and resources that could be better spent on core business initiatives.
Why Choose HWS for Your AWS Transfer Family Setup?
Implementing AWS Transfer Family involves more than just spinning up a server—it requires thoughtful architecture, secure identity integration, and scalable design. Here’s how HWS adds value:
• Expert Architecture Design: HWS architects tailor your AWS Transfer Family setup to meet your specific security, compliance, and performance needs—whether public-facing or VPC-hosted.
• Custom Identity Integration: We specialize in building Lambda-based identity providers that connect to your existing systems (e.g., Microsoft Entra ID, Secrets Manager, or custom databases).
• Accelerated Deployment: With proven templates and automation, HWS reduces setup time and ensures best practices are followed from day one.
• Security & Compliance: Our team ensures your file transfer workflows meet industry standards, with fine-grained IAM roles and audit logging.
• Ongoing Support & Optimization: From performance tuning to cost optimization, HWS provides continuous support to keep your solution running smoothly.
Whether you’re exchanging data with external partners or internal systems, HWS transforms AWS Transfer Family into a strategic asset for your organization.
Introducing AWS Transfer Family & SFTP
AWS Transfer Family eliminates this undifferentiated heavy lifting. It is a fully managed service supporting SFTP, FTPS, FTP and AS2 protocols, enabling secure file transfer directly into AWS storage services. You can setup public endpoint accessible over internet or setup SFTP instance inside a VPC for internal purpose or expose via Elastic IP addresses for certain IP addresses only (using security groups). As a cornerstone of secure data exchange, SFTP provides encryption for data in transit, ensuring confidentiality and integrity. AWS provides AWS Transfer Family Web Apps as add-on which can be enabled if you want to setup custom & simple web-based interface for transferring data to and from Amazon S3 over a web browser. AWS transfer family support custom identity providers which can be AWS API Gateway or an AWS Lambda function directly. As backend storage, it supports AWS S3 and AWS EFS (Elastic File System). AWS transfer family also provides connectors. The purpose of a connector is to establish a relationship between your AWS storage and a partner’s SFTP server. You can send files from AWS S3 to an external, partner owner destination. You can also use SFTP connector to retrieve files from a partner’s SFTP server.
Why Public Endpoint with direct Lambda Authentication? Benefits and Use-Cases
While AWS transfer family supports a variety of identity providers, using a public endpoint with a direct AWS Lambda integration offers a unique combination of accessibility and control. It is easy to setup and offer flexibility with no operational overhead.
· Ultimate Flexibility: You can write custom code to connect to any identity source, whether it’s a proprietary database, a third-party API, or a service like AWS Secrets Manager.
· Dynamic Authorization: Go beyond simple authentication. Your Lambda function can dynamically generate and assign fine-grained permissions on a per-user, per-session basis, defining exactly what S3 prefixes a user can access.
· Serverless Operations: By leveraging Lambda, your authentication mechanism becomes completely serverless. It scales automatically with demand, and you only pay for the compute time you consume, eliminating the need to manage another server.
· External Accessibility: A public endpoint makes your SFTP server accessible over the internet, which is essential for working with external partners and customers who cannot connect through a private VPC.
Understanding the Core Components for a Robust SFTP Solution
Before diving into the implementation, it’s essential to understand the roles of the key AWS services that form our solution.
AWS Transfer Family: Your Managed SFTP Server
AWS Transfer Family is the central component, providing the managed SFTP server endpoint. It handles all the underlying infrastructure, protocol negotiations, and client connection management. You configure the server’s endpoint (publicly accessible or VPC-hosted), choose your protocols (SFTP in our case), and define how users will be authenticated. This service abstracts away the complexity of running a highly available and scalable file transfer service.
Amazon S3: The Scalable and Secure Storage Backend
Amazon S3 serves as the durable and scalable storage layer for all files transferred through the SFTP server. When a user uploads a file, it is written directly to an S3 bucket. This native integration means you can immediately leverage other AWS services like AWS Glue for ETL, Amazon SageMaker for machine learning, or Amazon Athena for analytics on your transferred data without needing to move it.
AWS Lambda: The Heart of Custom Identity Management
AWS Lambda is the engine of our custom authentication logic. When a user attempts to log in to the SFTP server, AWS Transfer Family invokes our Lambda function via an API Gateway endpoint. The function receives the user’s provided credentials (like a password), validates them against a chosen identity source, and returns a response to Transfer Family. This response dictates whether the login is successful and specifies the user’s access level, including their home directory and the IAM role that defines their permissions within Amazon S3.
Architectural Deep Dive: Public Endpoint with Direct Lambda Authentication
Understanding the flow of information is key to troubleshooting and securing the system.
High-Level Flow: User Connection to S3 Storage
1. Connection Request: An SFTP user connects to the public endpoint of the AWS Transfer Family server using their client software, providing a username and password.
2. Authentication Trigger: AWS Transfer Family receives the request and, as configured, calls the specified API Gateway endpoint, forwarding the user’s credentials.
3. Lambda Invocation: API Gateway triggers the associated AWS Lambda function, passing the authentication request details in the event payload.
4. Identity Verification: The Lambda function executes your custom code. It parses the username and password, then validates them against your identity source (e.g., querying a database, checking a secret in Secrets Manager).
5. Authorization Response: If authentication is successful, the Lambda function constructs a JSON response. This response must include an IAM role ARN granting S3 permissions and can optionally specify the user’s home directory within the S3 bucket.
6. Session Granted: AWS Transfer Family receives the successful response from Lambda and grants the user a session. The permissions for this session are strictly scoped to the IAM role returned by the Lambda function.
7. File Transfer: The user can now perform file operations (upload, download, list), and all actions are translated into S3 API calls under the assumed IAM role.
Step-by-Step Implementation Guide: Building Your SFTP Server
This section provides a high-level guide to configuring the necessary components.
Preparing Your Amazon S3 Storage
First, create an S3 bucket to serve as the storage backend. It’s best practice to create a logical folder structure within the bucket to house user directories, for example, /my-sftp-bucket/home/.
Developing the AWS Lambda Identity Provider Function
Create a Lambda function that will handle authentication. This function needs an IAM execution role that allows it to write logs to CloudWatch. The core logic involves:
1. Parsing the incoming event from AWS transfer family SFTP server to extract username and password.
2. Validating the password. For simplicity, you could use a hardcoded dictionary, but a production system should query a secure source like AWS Secrets Manager or a database or Microsoft Entra ID (via Graph API).
3. If valid, return a JSON object with Role, HomeDirectory, and optionally a Policy field for inline session policies. The Role must be an ARN of an IAM role that Transfer Family can assume.
Configuring the AWS Transfer Family SFTP Server
1. In the AWS Transfer Family console, create a new server.
2. Select SFTP as the protocol.
3. For the identity provider, choose Custom identity provider and select your Lambda function.
4. Choose a Publicly accessible endpoint for SFTP server instance.
5. Select Amazon S3 as the storage backend.
6. Finalize the configuration, including any logging roles.
User Provisioning and Home Directory Configuration
User provisioning is managed entirely by your identity backend. When you add a user to your database or secrets store, they can be authenticated by your Lambda. The Lambda function is responsible for mapping a username to a specific home directory in S3. A common pattern is to return HomeDirectory: /${transfer:HomeBucket}/${transfer:UserName} to automatically map users to a folder matching their username within the designated S3 bucket.
Testing Your Public SFTP Endpoint
Once the server is created, use its public DNS hostname to connect with any standard SFTP client (e.g., FileZilla, WinSCP, or the command-line sftp). Use the credentials for a user defined in your identity source. A successful connection and the a
Considerations, Performance, and Cost Optimization
This serverless architecture is highly cost-effective. You pay for AWS Transfer Family based on the hours the endpoint is active, and the amount of data transferred. You also incur standard costs for S3 storage, API Gateway requests, and AWS Lambda execution time. Because all components scale on demand, you avoid paying for idle capacity.
Conclusion
By combining AWS Transfer Family with a direct AWS Lambda authentication provider, you can build a highly secure, scalable, and flexible public-facing SFTP server. This architecture removes the operational burden of managing traditional servers while providing granular control over user authentication and authorization. You gain the ability to integrate with any identity system, enforce the principle of least privilege with dynamic IAM policies, and leverage the full power of the AWS ecosystem for your data. This serverless approach not only modernizes your file transfer workflows but also strengthens your security posture, ensuring that your data exchanges are both efficient and protected against emerging threats.
