diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index e9cef1c..15a8a89 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -75,6 +75,16 @@ title — the CalVer tag is not created until `make image` runs after the merge.
 
 The types above are for `dev`, where a commit really does do one thing.
 
+## Deploying
+
+The server keeps its own `compose.yaml` and `.env`. Neither is pulled from
+here, so a release that renames a variable, adds one, or changes a mount
+needs both copied across **in the same deploy** — otherwise the container
+comes up against the old names and the app refuses to start.
+
+Anything in this repository that reaches the server by hand belongs in the
+release notes, flagged as breaking.
+
 ## Things that are easy to get wrong
 
 - **The interface is Finnish.** Code, comments, this file and the PRD are