Merge pull request #555 from opengisch/doc/document-webdav

Add WebDAV storage to architecture doc

Author: suricactus

documentation/assets/images/qfc_server_architecture_light.svg

@@ -8,9 +8,9 @@ tx_slug: documentation_reference_qfieldcloud_architecture
 QFieldCloud has a containerized architecture with multiple containers and volumes.
 
 
-!![QFieldCloud architecture: Rounded rectangles represent containers, ellipses represent volumes. The text in the square brackets is the service name found in the `docker-compose.yml` file, the rest of the text is the function of the container. Arrows between containers shows who initiates the communication. Arrows between a container and a volume represents whether the container reads (arrow pointing to container) or writes (arrow pointing to volume) data. Arrows and containers in gray represent deprecated services.](../../assets/images/qfc_server_architecture_light.svg)
+!![QFieldCloud architecture: Rounded rectangles represent containers, ellipses represent volumes. The text in the square brackets is the service name found in the `docker-compose.yml` file, the rest of the text is the function of the container. Arrows between containers shows who initiates the communication. Arrows between a container and a volume represents whether the container reads (arrow pointing to container) or writes (arrow pointing to volume) data. Arrows and containers in gray represent deprecated services. Arrows and containers in dashed line represent optional services.](../../assets/images/qfc_server_architecture_light.svg)
 
-See an interactive version of [the drawing above](https://excalidraw.com/#json=D2nvh_kmi5HAFVQne4atD,D9gsC0i14V491ZsCp-FLMw).
+See an interactive version of [the drawing above](https://excalidraw.com/#json=7rUYYLuU9kkRrvR3acb8R,6l4zHy4gvz8WYcb9z5O1jQ).
 
 !!! note
   For simplicity and clarity all graphs show the so called "happy path" without detailing the error handling through the process.
@@ -131,6 +131,19 @@ If `minio` is running, please make sure the host's firewall allows port `8009`,
 Single shot container to create the required buckets on the Object Storage under **[`minio`] File Storage**.
 
 
+#### [`webdav`] Alternative File Storage
+
+Local WebDAV storage used for development, using WebDAV protocol and specifications.
+
+The data is stored on the **[`webdav_data`]** volume.
+
+Can alternatively be used in place of the `minio` File Storage for storing the files. Can optionally be used for storing only attachments on it.
+
+!!! info
+    The webdav storage is optional, it is not a requirement for the system to work properly.
+
+If used, the webdav storage service should be replaced by a proper WebDAV server, e.g. NextCloud.
+
 #### [`db`] App PostgreSQL
 
 Local PostgreSQL database server to host the data for the **[`app`] QFieldCloud App**.
@@ -160,6 +173,11 @@ Stores dynamically created user PostGIS databases.
 Stores data for the **[`minio`] S3 service**.
 
 
+#### [`webdav_data`]
+
+Stores data for the **[`webdav`] storage service** if present.
+
+
 #### [`postgres_data`]
 
 Stores data for **[`db`] App PostgreSQL**.