Infrastructure security in AWS Transfer Family - AWS Transfer Family
NLB and NAT considerations

Infrastructure security in AWS Transfer Family

As a managed service, AWS Transfer Family is protected by AWS global network security. For information about AWS security services and how AWS protects infrastructure, see AWS Cloud Security. To design your AWS environment using the best practices for infrastructure security, see Infrastructure Protection in Security Pillar AWS Well‐Architected Framework.

You use AWS published API calls to access AWS Transfer Family through the network. Clients must support the following:

  • Transport Layer Security (TLS). We require TLS 1.2 and recommend TLS 1.3.

  • Cipher suites with perfect forward secrecy (PFS) such as DHE (Ephemeral Diffie-Hellman) or ECDHE (Elliptic Curve Ephemeral Diffie-Hellman). Most modern systems such as Java 7 and later support these modes.

Additionally, requests must be signed by using an access key ID and a secret access key that is associated with an IAM principal. Or you can use the AWS Security Token Service (AWS STS) to generate temporary security credentials to sign requests.

Avoid placing NLBs and NATs in front of AWS Transfer Family servers

Note

Servers configured with FTP and FTPS protocols only allow a configuration with a VPC: there is no public endpoint available for FTP/FTPS.

Many customers configure a Network Load Balancer (NLB) to route traffic to their AWS Transfer Family server. They typically do this either because they created their server before AWS offered a way to access it from both inside their VPC and from the internet, or to support FTP on the internet. This configuration not only increases costs for customers, but can also cause other issues, which we describe in this section.

NAT gateways are a mandatory component when clients are connecting from a customer private network behind a corporate firewall. However, you should be aware that when many clients are behind the same NAT gateway, this can impact performance and connection limits. If there's an NLB or NAT in the communication path from the client to the FTP or FTPS server, the server can't accurately recognize the client's IP address, because AWS Transfer Family sees only the IP address of the NLB or NAT.

If you're using the configuration of a Transfer Family server behind an NLB, we recommend that you move to a VPC endpoint and use an Elastic IP address instead of using an NLB. When using NAT gateways, be aware of the connection limitations described below.

If you're using the FTPS protocol, this configuration not only reduces your ability to audit who's accessing your server, but it can also impact performance. AWS Transfer Family uses the source IP address to shard your connections across our data plane. For FTPS, this means that instead of having 10,000 simultaneous connections, Transfer Family servers with NLB or NAT gateways on the communication route are limited to only 300 simultaneous connections.

Although we recommend avoiding Network Load Balancers in front of AWS Transfer Family servers, if your FTP or FTPS implementation requires an NLB or NAT in the communication route from the client, follow these recommendations:

  • For an NLB, use port 21 for health checks, instead of ports 8192-8200.

  • For the AWS Transfer Family server, enable TLS session resumption by setting TlsSessionResumptionMode = ENFORCED.

    Note

    This is the recommended mode, as it provides enhanced security:

    • Requires clients to use TLS session resumption for subsequent connections.

    • Provides stronger security guarantees by ensuring consistent encryption parameters.

    • Helps prevent potential downgrade attacks.

    • Maintains compliance with security standards while optimizing performance.

  • If possible, migrate away from using an NLB to take full advantage of AWS Transfer Family performance and connection limits.

For additional guidance on NLB alternatives, contact the AWS Transfer Family Product Management team through AWS Support. For more information about improving your security posture, see the blog post Six tips to improve the security of your AWS Transfer Family server.