begin phasing in config of vpn via cdist

doc/uncloud-manual-2020-08-01.org

@@ -170,7 +170,7 @@ VPNNetworks can be managed by all authenticated users.
 * Developer Handbook
   The following section describe decisions / architecture of
   uncloud. These chapters are intended to be read by developers.
-** Documentation
+** This Documentation
    This documentation is written in org-mode. To compile it to
    html/pdf, just open emacs and press *C-c C-e l p*.
 ** Models
@@ -234,6 +234,53 @@ VPNNetworks can be managed by all authenticated users.
 *** Decision
     We use integers, because they are easy.
 
+** Distributing/Dispatching/Orchestrating
+*** Variant 1: using cdist
+    - The uncloud server can git commit things
+    - The uncloud server loads cdist and configures the server
+    - Advantages
+      - Fully integrated into normal flow
+    - Disadvantage
+      - web frontend has access to more data than it needs
+      - On compromise of the machine, more data leaks
+      - Some cdist usual delay
+*** Variant 2: via celery
+    - The uncloud server dispatches via celery
+    - Every decentral node also runs celery/connects to the broker
+    - Summary brokers:
+      - If local only celery -> good to use redis    - Broker
+      - If remote: probably better to use rabbitmq
+    - redis
+      - simpler
+    - rabbitmq
+      - more versatile
+      - made for remote connections
+      - quorom queues would be nice, but not clear if supported
+        - https://github.com/celery/py-amqp/issues/302
+        - https://github.com/celery/celery/issues/6067
+      - Cannot be installed on alpine Linux at the moment
+    - Advantage
+      - Very python / django integrated
+      - Rather instant
+    - Disadvantages
+      - Every decentral node needs to have the uncloud code available
+      - Decentral nodes *might* need to access the database
+        - Tasks can probably be written to work without that
+          (i.e. only strings/bytes)
+
+**** log/tests
+     (venv) [19:54] vpn-2a0ae5c1200:~/uncloud$ celery -A uncloud -b redis://bridge.place7.ungleich.ch worker -n worker1@%h --logfile ~/celery.log -
+Q vpn-2a0ae5c1200.ungleich.ch
+
+
+*** Variant 3: dedicated cdist instance via message broker
+    - A separate VM/machine
+    - Has Checkout of ~/.cdist
+    - Has cdist checkout
+    - Tiny API for management
+    - Not directly web accessible
+    - "cdist" queue
+
 ** Milestones                                                       :uncloud:
 *** 1.1 (cleanup 1)
 **** TODO [#C] Unify ValidationError, FieldError - define proper Exception