01 / CONTEXT
The project required an internet-facing service for external file transfer. The solution was built around SFTP provided by OpenSSH on a Linux host.
Making the service reachable from an untrusted network meant that the work could not stop at simply installing and exposing SSH. Authentication, network exposure and repeated login attempts also had to be considered.
02 / OBJECTIVE
The objective was to provide a simple and reliable method of transferring files over the Internet while keeping the exposed service and surrounding configuration as limited as possible.
The design focused on providing the required functionality without introducing unnecessary services or additional externally reachable components.
03 / IMPLEMENTATION
The service was deployed on Linux using OpenSSH and its built-in SFTP functionality. Additional host-level controls were then added around the service.
OpenSSH / SFTP. Configured the Linux host and OpenSSH service to provide the required file-transfer functionality.
Key-based authentication. SSH keys were configured for access to the service instead of relying on ordinary password-based authentication for the intended connection method.
Host firewall. UFW was used to control inbound network access and reduce unnecessary exposure at the host level.
Fail2ban. Fail2ban was added to react automatically to repeated failed authentication attempts.
04 / SECURITY CONTROLS
The security of the deployment was treated as a combination of controls surrounding the service rather than a single configuration change.
Authentication. SSH keys provided a controlled authentication method for access to the file-transfer service.
Network exposure. UFW provided host-level filtering for traffic reaching the server.
Repeated login attempts. Fail2ban added an automated response layer for repeated authentication failures.
This case study is intentionally sanitized. Production addresses, hostnames, usernames, SSH keys, organization details and other environment-specific values are not included.
05 / RESULT
The result was a deployed internet-facing SFTP service running on Linux with key-based SSH authentication, host-level firewall controls and Fail2ban protection.
The final setup kept the solution focused on the required file-transfer functionality while adding separate controls around authentication, network access and repeated failed login attempts.
06 / TAKEAWAYS
The main lesson from this deployment was that exposing a service securely involves more than configuring the service itself.
Authentication, firewall rules, abuse prevention and the information exposed in documentation all form part of the security of the final system.
It also provided practical experience with building a small production Linux service from the ground up and considering how that service would behave once exposed to an untrusted network.