AB#2114 Add QEMU metadata API (#237)

* Add QEMU metadata API

* API server is started automatically when using terraform to deploy a QEMU cluster

* Enable QEMU metadata usage for disk-mapper, debugd and the Coordinator

Signed-off-by: Daniel Weiße <dw@edgeless.systems>

hack/qemu-metadata-api/README.md

@@ -0,0 +1,50 @@
+# QEMU metadata API
+
+This program provides a metadata API for Constellation on QEMU.
+
+## Dependencies
+
+To interact with QEMU `libvirt` is required.
+Install the C libraries:
+
+On Ubuntu:
+
+```shell
+sudo apt install libvirt-dev
+```
+
+On Fedora:
+
+```shell
+sudo dnf install libvirt-devel
+```
+
+## Firewalld
+
+If your system uses `firewalld` virtmanager will add itself to the firewall rules managed by `firewalld`.
+Your VMs might be unable to communicate with the host.
+
+To fix this open port `8080` (the default port for the QEMU metadata API) for the `libvirt` zone:
+
+```shell
+# Open the port
+sudo firewall-cmd --zone libvirt --add-port 8080/tcp --permanent
+```
+
+## Docker image
+
+Build the image:
+
+```shell
+DOCKER_BUILDKIT=1 docker build -t ghcr.io/edgelesssys/constellation/qemu-metadata-api:latest -f hack/qemu-metadata-api/Dockerfile .
+```
+
+A container of the image is automatically started by Terraform.
+You can also run the image manually using the following command:
+
+```shell
+docker run -it --rm \
+    --network host \
+    -v /var/run/libvirt/libvirt-sock:/var/run/libvirt/libvirt-sock \
+    ghcr.io/edgelesssys/constellation/qemu-metadata-api:latest
+```