docs: add operating.md

README.md

@@ -73,6 +73,7 @@ and in README files for individual Ansible roles:
 * [Docker usage](roles/docker/README.md)
 * [CLI tool usage](docs/cli.md)
 * [Testing](docs/testing.md)
+* [Operating](docs/operating.md)
 
 ### Built-in services documentation
 

docs/operating.md

+Operating float
+===============
+
+This document covers operational aspects of running float, and how
+these operations can impact users of the services.
+
+# Unreachable hosts
+
+Configurations that depend on data from *other* hosts (e.g. the vpn
+service *tinc* needs to know about all hosts) can diverge when some
+hosts cannot be reached by float.
+
+In this situation there's effectively a *partition* between the
+configurations: care must be applied to make sure that they still make
+sense and the service behaves correctly. Once the hosts are reachable
+again then the next float run will bring the configurations back in
+sync.