📝 add architecture overview in README

README.md

@@ -3,9 +3,27 @@
 keywords: `cdevents`, `sdlc`
 status: wip
 
-A set of components to provide a view of which version of my service is deployed and where.
+A set of components to provide a view of which version of services are deployed and which environment, what test ran,...
 
 - Collect events ([cdevents]) related to the deployment of artifacts (service, ...)
 - Dashboard to query and visualize events and states over time
 
+## Architecture Overview
+
+[![](doc/images/Drawing%202023-12-27%2016.04.47-cdviz-architecture.excalidraw.svg)](doc/images/Drawing%202023-12-27%2016.04.47-cdviz-architecture.excalidraw.svg)
+
+**Why dashboard tool (like Grafana) have a read-only access to the DB (postgresql), and go through an API (micro)service (like cdviz-collector)?**
+
+- access to the data is the value, not the service
+- allow dashboards to use the full query power of SQL to query data, and to plug any analytics tools
+- allow Data Ops to split the DB with read-only replicas if needed,...
+- no need to create and provide a new custom (and always incomplete, frustrated) query language
+  - no need to maintain a custom query language on the service side
+  - no need to maintain a connector (`datasource`) for callers (analytics tools,...)
+  - no need to re-invent (or to "encapsulate") what DB managers do better
+- enforce the read-only view of the DB to be like a public API
+  - require to configure access control
+  - require to document and expose table structure (like an API) and to provide samples of queries, maybe function,...
+- service can provide helpers endpoint for some complex query or additional "view"
+
 [cdevents]: <https://cdevents.dev/>