Issue 086: taking a module narrows a port the predecessor served, without saying so

2026-09-22 19:00:59 +02:00
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+---
+status: open
+opened: 2026-09-22
+located-in: []
+fixed-by:
+amended-design:
+---
+
+# 086 — Taking a module narrows a port the predecessor served, without saying so
+
+## What was observed
+
+In the adoption lab bed, 2026-09-22. A service found on the machine served its port to anyone,
+and the predecessor's firewall allowed it from anywhere. The catalogue module that replaces it
+declares the port reachable from the private network only. After the module was **taken**, the
+mesh's guard refused that port from everywhere outside the private network. That is
+[ADR 0103](../../02-DECISIONS/0103-what-an-adopted-node-holds-and-what-its-guard-refuses.md)
+working as written: a taken module's published private-network ports are guarded. The service
+answered over the private network, and the bed passed.
+
+Nothing said the port had narrowed. Taking a module names the files and containers it replaces,
+but not the ports whose reach changes. The converge preview names every narrowing, but the flip
+comes after taking, so by then the change has already happened.
+
+## Why it matters beyond this instance
+
+On a machine in use, taking a module is the cutover for that service. If the predecessor served
+the port publicly and the module says private, taking it closes the port to every client outside
+the private network. Nothing warns the operator first. ADR 0100 promises that each step says what
+it changes before it changes it, and for taking a module this one does not.
+
+## Open questions
+
+- Should taking a module preview the reach of each port it publishes, found firewall and guard
+  included, and ask for the same kind of confirmation as the flip?
+- Or should taking refuse while a port of the module is reachable more widely than the module
+  declares, until the operator either changes the module's exposure or confirms the narrowing?