add cache

architecture.md

@@ -193,6 +193,14 @@ Considered alternatives include:
 - 389 DS: older larger package
 - FreeIPA: wrapper around 389 DS
 
+### [Attic](https://github.com/zhaofengli/attic)
+
+Attic is a multi-tenant Nix cache featuring recency-based garbage collection written in Rust.
+
+Considered alternatives include:
+
+- cache-server: distributed cache written in Python that seems more of a research project than an actively maintained repository.
+
 ## Architecture
 
 At the core of Fediversity lies a NixOS configuration module for a set of selected applications.