Merge pull request 'Issue 122: a module cannot ask for its own public name' (#121) from issue/122-a-module-cannot-ask-for-its-own-public-name into main

2026-09-26 12:58:41 +00:00
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 status: located
 opened: 2026-09-26
 located-in: [mesh-controller internal/catalogue/declaration.go, mesh-catalog modules/keycloak, mesh-catalog modules/minio, mesh-catalog modules/nextcloud]
 fixed-by:
 amended-design:
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 # 122 — A module cannot ask for its own public name, so three manifests wrote this mesh's names into the catalogue
 ## What was observed
 Reviewing the open module changes on 2026-09-26, three of them independently put a name belonging to
 **one particular mesh** into a module definition, each for a different piece of software and each as
 the only way to make the software work:
 - The identity provider's manifest gains `KC_HOSTNAME: https://<label>.<public-domain>` as a literal,
  because the software generates absolute URLs and, behind a proxy, cannot derive them.
 - The object store's manifest gains `MINIO_BROWSER_REDIRECT_URL: https://<label>.<public-domain>` as
  a literal, for the same reason — its console redirects to an absolute URL.
 - The file-sync module's S3 bucket is renamed from `nextcloud` to a name carrying this mesh's own
  name, so the module matches a bucket that already exists here.
 No reviewer introduced these carelessly: each is the value the software needs, and there is nowhere
 else to put it.
 ## What the mesh offers instead, and why none of it answers
 A manifest may interpolate `${secret:…}`, `${seat:…}`, `${bound:…}`, `${port:…}` and
 `${machine:…}`. The machine form resolves `at`, `name` and `address` — the machine's identity on the
 **private** network. None of them yields a public name.
 The mesh does compose public names: a route contribution's label is joined to the node's public
 domain, `<label>.<public-domain>`, and the mesh interprets neither half. That happens inside the
 controller when a declaration is built, and the result reaches the proxy that serves the route. It
 does not reach the module that asked for the route, so a module that must **tell its own software**
 what it will be reached at cannot read what the mesh already worked out.
 So the workaround is the only expressible option: write the answer down, in the definition, for the
 one mesh it is true of.
 ## Why it matters beyond these three
 A module definition is meant to hold what is true of the module everywhere, with everything
 particular to an installation resolved at assignment — the argument
 [ADR 0112](../../02-DECISIONS/0112-a-module-definition-names-no-node-mesh-or-path.md) (proposed)
 makes in full, and what [issue 119](../119-a-module-definition-decides-where-its-files-live/00-report.md)
 found for paths. A hostname is the same kind of fact as a path, and arriving by the same route: not
 because anyone disagreed with the principle, but because the mechanism that would honour it does not
 exist yet.
 The cost is concrete. A second mesh installing the identity provider from this catalogue gets the
 first mesh's hostname, and its login flow breaks in a way that looks like a proxy fault. Nothing
 checks for it: a literal hostname in an env value is a well-formed string, and no rule distinguishes
 it from a version number.
 The bucket case is the same shape with a different subject — an adopted resource's real name is also
 particular to one installation, and also has nowhere to live but the definition.
 ## Open questions
 - Should a module be able to name what it will be reached at — a `route`-scoped interpolation
  resolving to the composed public name of a route it contributes, so the answer the mesh already
  computes is the one the software is told? That is the smallest fix and it stays within the existing
  vocabulary.
 - Does the scheme belong to it? Every instance here wrote `https://`, which is true of a route the
  proxy terminates and not of the module's own port.
 - For an adopted resource such as an existing bucket: is that a setting on the assignment (where
  ADR 0112 would put it), and if so what reads it — the provisioner, or the module's own values?
 - What check would notice the next one? A definition naming a public domain is detectable in the
  shape of the value, which is more than nothing, and less than a rule.