docs: add faq (#288)

README.md

@@ -28,6 +28,7 @@ This repository is the starting point for any information and tools you will nee
     - [Auto-Updates](#auto-updates)
     - [Auto-Backups](#auto-backups)
     - [Non-Linux OS](#non-linux-os)
+    - [FAQ](#faq)
 5. [Troubleshooting](#troubleshooting)
     - [Docker Daemon Proxy Configuration](#docker-daemon-proxy-configuration)
     - [Monitoring](#monitoring)
@@ -417,6 +418,54 @@ We have tested the installation procedure with an Ubuntu 22.04 guest system runn
 
 Installation under WSL ought to work, but we have not tested this.
 
+### FAQ
+
+**Q: How is the security of GitHub pulls, volumes/containers, and image signing ensured?**
+
+A: Changes to Git branches that could be delivered to sites (main and develop) must be accepted via a pull request with at least two positive reviews.
+Containers/images are not built manually, but rather automatically through a CI/CD pipeline, so that an image can be rolled back to a defined code version at any time without changes.
+**Note:** If firewall access for (outgoing) connections to GitHub and/or Docker Hub is problematic at the site, mirrors for both services are available, operated by the DKFZ.
+
+**Q: How is authentication between users and components regulated?**
+
+A: When setting up a Bridgehead, a private key and a so-called Certificate Sign Request (CSR) are generated locally. This CSR is manually signed by the broker operator, which allows the Bridgehead access to the network infrastructure.
+All communication runs via Samply.Beam and is therefore end-to-end encrypted, but also signed. This allows the integrity and authenticity of the sender to be technically verified (which happens automatically both in the broker and at the recipients).
+The connection to the broker is additionally secured using traditional TLS (transport encryption over https).
+
+**Q: Are there any statistics on incoming traffic from the Bridgehead (what goes in and what goes out)?**
+
+A: Incoming and outgoing traffic can only enter/leave the Bridgehead via a forward or reverse proxy, respectively. These components log all connections.
+Statistical analysis is not currently being conducted, but is on the roadmap for some projects. We are also working on a dashboard for all tasks/responses delivered via Samply.Beam.
+
+**Q: How is container access controlled, and what permission level is used?**
+
+A: Currently, it is not possible to run the Bridgehead "out-of-the-box" as a rootless Docker Compose stack. The main reason is the operation of the reverse proxy (Traefik), which binds to the privileged ports 80 (HTTP) and 443 (HTTPS).
+Otherwise, there are no known technical obstacles, although we don't have concrete experience implementing this.
+At the file system level, a "bridgehead" user is created during installation, which manages the configuration and Bridgehead folders.
+
+**Q: Is a cloud installation (not a company-owned one, but an external service provider) possible?**
+
+A: Technically, yes. This is primarily a data protection issue between the participant and their cloud provider.
+The Bridgehead contains a data storage system that, during use, contains sensitive patient and sample data.
+There are cloud providers with whom appropriately worded contracts can be concluded to make this possible.
+Of course, the details must be discussed with the responsible data protection officer.
+
+**Q: What needs to be considered regarding the Docker distribution/registry, and how is it used here?**
+
+A: The Bridgehead images are located both in Docker Hub and mirrored in a registry operated by the DKFZ.
+The latter is used by default, avoiding potential issues with Docker Hub URL activation or rate limits.
+When using automatic updates (highly recommended), an daily check is performed for:
+- site configuration updates
+- Bridgehead software updates
+- container image updates
+
+If updates are found, they are downloaded and applied.
+See the first question for the control mechanism.
+
+**Q: Is data only transferred one-way (Bridgehead/FHIR Store → Central/Locator), or is two-way access necessary?**
+
+A: By using Samply.Beam, only one outgoing connection to the broker is required at the network level (i.e., Bridgehead → Broker).
+
 ## Troubleshooting
 
 ### Docker Daemon Proxy Configuration