service/donate.md

@@ -321,7 +321,19 @@ logs, and CAPTCHA tokens.
 
 ## Queues
 
-Redis is used as a queue.
+Redis is used as a queue to process transactions from the frontend to
+the CiviCRM backend. It handles those types of transactions:
+
+- one-time donations
+- recurring donations
+- mailing list subscriptions (essentially a backend for
+  https://newsletter.torproject.org/)
+
+The Redis server runs on the CiviCRM server, and is accessed through
+an IPsec tunnel, see the [authentication](#authentication) section below as
+well. The Django application reimplements the [resque](https://resque.github.io/) queue
+(originally written in Ruby, but ported to PHP by GiantRabbit) to pass
+messages to the CiviCRM backend.
 
 TODO: describe better the resque stuff.
 
@@ -378,7 +390,8 @@ about the development setup.
 
 ## Related services
 
-See mainly the [CiviCRM server](service/crm).
+See mainly the [CiviCRM server](service/crm), which provides the backend for
+this service, handling perks, memberships and mailings.
 
 ## Issues