ADR 0167: a membership carries what its module receives, and who the mesh is

Issue 191's route proxy needs to know who the mesh is to serve an internal name correctly, and the first fix had it work that out alone. The membership on the bus now carries it, from the same list the filter uses. ADR 0138 gains an insight that the proxy is where internal reach is kept; designs 08 and 25 say how.
2026-10-02 01:48:03 +02:00
parent 496d136d72
commit e6b638e63c
7 changed files with 195 additions and 5 deletions
@@ -124,6 +124,32 @@ This corrects a fact, not the decision: one statement per endpoint, three things
 none of them deciding on its own, all stand. The table in the decision should be read with the filter
 column applying to an unrouted endpoint.

+## Progressive insight — 2026-10-02, from issue 191
+
+**For a routed endpoint, "the proxy serves the internal name" has to mean "serves it to the private
+network", and only the proxy can make it mean that.** The decision says `internal` means the proxy
+serves the internal name and not the public one. It does not say to whom, and the proxy answered
+every name it routes to any request that carried it, on the same listeners as its public names. A
+name being internal kept nobody out: a request from the internet only had to send it. While every
+routed endpoint also had a public name, nothing showed it. Once an endpoint could be internal alone
+([issue 191](../04-ISSUES/191-a-route-with-only-an-internal-name-is-dropped/00-report.md)), serving
+its name to everyone would have published exactly what `internal` was chosen to keep private.
+
+The earlier insight above says the port is not the path for a routed endpoint. This is its other
+half: the proxy is the path, so the proxy is where `internal` is enforced. It serves an internal name
+only to the machines of the mesh and to the machine itself
+([ADR 0144](0144-anything-on-a-machine-may-call-anything-on-it.md)). Who the mesh is, it is told,
+not left to work out: its membership carries the same list of machine addresses the filter's "from the
+mesh" is rendered from ([ADR 0167](0167-a-membership-carries-what-its-module-receives-and-who-the-mesh-is.md)).
+To anyone else, the name is answered as one never routed, in the handshake and in the request, and not
+listed among the names it serves. This holds for the internal name of a `both` endpoint too, whose
+outsiders have its public name.
+
+The decision, the options and the consequences stand: one statement per endpoint, three things
+derived from it. Checked in the proxy's own tests: an internal-only name is served to a machine the
+membership names and to loopback, and refused, unlisted and uncertified for any other request; until
+the mesh is issued, it is served to the machine alone.
+
 ## Consequences

 - **A manifest gains endpoint names, and a route contribution names an endpoint instead of a port.**
@@ -0,0 +1,99 @@
+---
+topic: the mesh
+status: accepted
+date: 2026-10-02
+deciders: jochen
+reconstructed: false
+extends: 02-DECISIONS/0160-the-mesh-issues-an-assignments-subjects-and-a-runtime-serves-what-it-is-issued.md
+---
+
+# 167. A membership carries what its module receives, and who the mesh is
+
+## Context
+
+A provider learns what it is given from a file. The controller composes every consumer's contribution
+to a requirement, and the node's declaration writes them into the provider's received file. The route
+proxy reads its routes that way: one JSON file, re-read every two seconds.
+
+[Issue 191](../04-ISSUES/191-a-route-with-only-an-internal-name-is-dropped/00-report.md) showed what
+that file leaves out. Since [ADR 0138](0138-an-assignment-binds-an-endpoint-and-says-how-far-it-reaches.md),
+a route whose endpoint reaches only the private network carries an internal name and no public one.
+The proxy dropped it. Serving it was not enough either: the proxy answers public and internal names on
+the same listeners, so an internal name served to every request is public under a guessable name. To
+serve it correctly the proxy needs a second fact, **who the mesh is**, and nothing gave it one.
+
+The first attempt had the proxy work it out: the mesh's range from an environment variable written by
+the catalogue, and the machine's container bridges read from its own interfaces. That is a second
+definition of "the mesh", kept by one module, beside the one the packet filter already uses. The
+controller resolves "from the mesh" to every machine's address on the private network, and the filter
+is rendered from that list. Two definitions agree until one changes.
+
+[ADR 0160](0160-the-mesh-issues-an-assignments-subjects-and-a-runtime-serves-what-it-is-issued.md)
+already gives every assignment one document on the bus, its membership, read once at connect and
+followed. It says what the assignment serves and reaches. It does not yet say what it is given.
+
+## Considered Options
+
+1. **Keep the file, add the mesh to it.** The proxy keeps polling a file, and the controller writes the
+   mesh's addresses beside the routes. It fixes the definition, but delivery stays a file re-read on a
+   timer, written by a separate path from the one every other fact a module is told now takes.
+2. **Have the proxy work it out** from a range in its environment and the machine's interfaces. Rejected:
+   it is the second definition this record exists to remove.
+3. **The membership carries it.** What each module receives, from the same composition its received
+   file is written from, and the mesh's addresses, from the same list the filter is rendered from. The
+   proxy follows its membership and serves exactly that.
+
+## Decision
+
+**Option 3.**
+
+- **A membership carries what its module receives**, by requirement: the contributions every consumer
+  made, exactly as composed for its received file. A requirement nobody contributed to is an empty
+  list, never absent, for the reason the file is written empty: "nothing asked" and "never told" want
+  different responses.
+- **A membership carries who the mesh is**: every machine's address on the private network, the list
+  a rule saying "from the mesh" resolves to. One list, two readers: the filter and any module that
+  must tell the mesh from the world.
+- **The route proxy reads its routes and the mesh from its membership**, with the bus account every
+  module that speaks on the bus is given. It serves an internal name only to the machines the mesh
+  names and to the machine itself, and answers anyone else as it answers a name it never routed: in
+  the request, in the handshake, and in the list of names it serves.
+- **The file stays until the bus has spoken.** While a proxy has read no membership that carries routes,
+  it serves the file, and an internal name only to its own machine: refused, never opened. A
+  membership from a controller that issues no routes changes nothing.
+
+## Consequences
+
+- Every membership grows two fields. A machine joining or leaving republishes every membership, which
+  a push already does.
+- A provider that receives something is told it twice for now, in its file and on the bus. The file
+  goes when every provider reads its membership; that is its own change.
+- The route proxy needs a bus account. It is issued like any module's, so a machine running the proxy
+  cannot be composed between the catalogue declaring the account and the operator issuing it. The
+  machine keeps what it runs meanwhile.
+- The internal name of a route that also has a public one is now served to the mesh only. Outsiders
+  have the public name.
+- A container on the same machine that calls that machine's own internal name arrives from its
+  container network, not from a mesh address, and is refused. Calls between machines are unaffected:
+  they leave by the machine's mesh address. Whether the mesh should also issue each machine's container
+  networks is left open, because the mesh does not record them today.
+
+## How this is checked
+
+| Rule | Checked by |
+|---|---|
+| What a provider receives on the bus is what its received file says, same-node port fix included | a controller test composing a provider and a consumer on one machine and comparing the two |
+| An internal name is served to the machines the membership names and to loopback, and to nobody else | the proxy's tests: served from a named address and from loopback; refused, unlisted and uncertified from any other |
+| A membership that carries no routes, or a mesh that cannot be read, changes nothing | the proxy's tests |
+| Until the mesh is issued, an internal name is served to the machine alone | the proxy's tests |
+| Live: an internal-only route answers over the mesh and is refused from outside | by hand, after the release |
+
+## References
+
+- [ADR 0160](0160-the-mesh-issues-an-assignments-subjects-and-a-runtime-serves-what-it-is-issued.md) —
+  the membership this extends
+- [ADR 0138](0138-an-assignment-binds-an-endpoint-and-says-how-far-it-reaches.md) — reach, and the
+  insight of 2026-10-02 that the proxy is where internal reach is kept
+- [ADR 0144](0144-anything-on-a-machine-may-call-anything-on-it.md) — the machine itself is always inside
+- [Issue 191](../04-ISSUES/191-a-route-with-only-an-internal-name-is-dropped/00-report.md) — what
+  found it
@@ -177,6 +177,7 @@ python3 00-META/checks/index.py            fail if stale
 - **0161** — [What deserves a seat: a role of a module is a seat, a singular fact about machines is a placement with a capacity of one, and a holder's software is the machine's](0161-what-deserves-a-seat.md)
 - **0162** — [A merge produces a tiered plan the mesh keeps, and a module's dependencies are one relation in the catalogue](0162-a-merge-produces-a-tiered-plan-the-mesh-keeps.md)
 - **0163** — [Taking a module over is a comparison: what it compares, what it refuses, and what it carries](0163-taking-a-module-over-is-a-comparison.md)
+- **0167** — [A membership carries what its module receives, and who the mesh is](0167-a-membership-carries-what-its-module-receives-and-who-the-mesh-is.md)

 ### Its tiers, from the bottom up

@@ -7,8 +7,9 @@ code:
  - mesh-controller internal/identity/authority.go
  - mesh-host internal/identity/serving.go
  - mesh-host internal/apply (the service that reflects a rule set)
-updated: 2026-09-30
+updated: 2026-10-02
 decisions:
+  - 02-DECISIONS/0167-a-membership-carries-what-its-module-receives-and-who-the-mesh-is.md
  - 02-DECISIONS/0148-the-meshs-names-are-resolved-not-copied-into-containers.md
  - 02-DECISIONS/0151-a-routes-internal-name-is-composed-under-the-node-that-serves-it.md
  - 02-DECISIONS/0147-a-module-anchors-the-meshs-authority.md
@@ -842,6 +843,18 @@ One value, three readers:
 | `public` | the machine port, to anywhere | the public name | the public authority |
 | `both` | the machine port, to anywhere | both names | each name's own authority |

+*2026-10-02.* **The proxy serves an internal name to the private network only**
+([ADR 0138](../../02-DECISIONS/0138-an-assignment-binds-an-endpoint-and-says-how-far-it-reaches.md),
+its insight of this date). It answers public and internal names on the same listeners, so the name a
+request carries is the request's own claim, not where the request came from. An internal name is
+served to the machines of the mesh and to the machine itself; to anyone else it is answered as a name
+never routed, in the handshake as well as the request. Without this, an endpoint with reach `internal`
+would be public under a name that is easy to guess
+([issue 191](../../04-ISSUES/191-a-route-with-only-an-internal-name-is-dropped/00-report.md)).
+The proxy is told who the mesh is, and its routes, in its membership on the bus — the same machine
+addresses the filter's "from the mesh" is rendered from
+([ADR 0167](../../02-DECISIONS/0167-a-membership-carries-what-its-module-receives-and-who-the-mesh-is.md)).
+
 **An endpoint that is not routed is reached and never named.** No route contribution means no name is
 composed and no certificate requested, while the filter still acts on it. That is the case the model
 could not express at all, and it is the ordinary case for anything that is not HTTP.
@@ -7,8 +7,9 @@ code:
  - mesh-tools src/broker-amqp.ts (to be replaced)
  - mesh-catalog modules/nats (to be written)
  - mesh-sdk src (the protocol's NATS binding, step 3)
-updated: 2026-10-01
+updated: 2026-10-02
 decisions:
+  - 02-DECISIONS/0167-a-membership-carries-what-its-module-receives-and-who-the-mesh-is.md
  - 02-DECISIONS/0160-the-mesh-issues-an-assignments-subjects-and-a-runtime-serves-what-it-is-issued.md
  - 02-DECISIONS/0157-a-build-says-what-it-does-on-the-bus-as-it-happens.md
  - 02-DECISIONS/0106-the-bus-is-nats.md
@@ -94,6 +95,12 @@ list; the account's grant is the same membership read the other way; the console
 tool's subject. The one rule a runtime keeps is the membership's own subject, from the two names in its
 credential.

+**Revised 2026-10-02** ([ADR 0167](../../02-DECISIONS/0167-a-membership-carries-what-its-module-receives-and-who-the-mesh-is.md)):
+a membership also carries **what its module receives**, by requirement — the contributions its
+received file is written from, from the same composition — and **who the mesh is**, every machine's
+address on the private network, the list the filter's "from the mesh" is rendered from. The route
+proxy is the first reader of both.
+
 **Revised 2026-09-27** ([ADR 0129](../../02-DECISIONS/0129-a-seat-carries-the-protocol-of-its-role.md)):
 **`mesh.build.request`, `mesh.control.built` and the BUILDS stream are gone.** A build is work submitted to a role, and the
 mesh already has a shape for that — a seat's `accept` subjects, on a work queue with a queue group of
@@ -1,9 +1,9 @@
 ---
 status: located
 opened: 2026-10-01
-located-in: [mesh-controller examples/route-proxy/main.go (routesFrom requires a route's public `name` and treats `internal-name` only as an alias of it)]
+located-in: [mesh-controller examples/route-proxy/main.go (routesFrom requires a route's public `name` and treats `internal-name` only as an alias of it; the handler serves every routed name to any source), mesh-controller internal/broker/membership.go (a membership says nothing of what its module receives or who the mesh is)]
 fixed-by:
-amended-design: []
+amended-design: [03-DESIGN/01-to-be/08-connectivity.md, 03-DESIGN/01-to-be/25-the-bus-on-nats.md]
 ---

 # 191 — A route with only an internal name is dropped as naming nothing
@@ -23,9 +23,53 @@ mesh before ADR 0138, when both names were always composed. It has been wrong si
 The other half of the proxy already handles the case. Certificates for a host are split by whether it
 is in the public set: hosts outside it go to the internal authority, and only hosts inside it are
 eligible for ACME. A host that is only ever an internal name falls on the correct side of both checks
-without change. Only reading the route was wrong.
+without change. For certificates, only reading the route was wrong; who may reach the route is the next section.

 **The fix.** `routesFrom` takes a route that names either host, serves each name it carries, and
 marks only the public one as public. It still skips a route that names neither, with the same log line.
 A test proves an internal-only route is served, certified by the internal authority, and refused by
 the public one. That test fails against the code before the change.
+
+## The first fix would have made the name public — 2026-10-02, from review
+
+Serving the dropped route was not enough. The proxy picks a route from the name a request carries
+and never from where the request came from, and it answers public and internal names on the same
+listeners. Its public names resolve to an address the internet reaches. So once the internal-only
+route was served, any request from the internet carrying `unifi.home-server.internal` — a name of a
+fixed, guessable shape — would have reached an administration interface that reach `internal` was
+chosen to keep private. Before the fix the route was unreachable from everywhere. After it, it would
+have been reachable from everywhere. Two more leaks came with it: the proxy's answer for an unrouted
+name listed every name it serves, internal ones included, and the handshake handed a certificate
+naming the internal host to any client.
+
+Nothing showed this while every routed endpoint also had a public name: its internal name exposed
+nothing the public one did not. It is a gap in the decision's wording, not only in the proxy — ADR
+0138 says the proxy *serves* the internal name without saying to whom — so it is recorded there as a
+progressive insight and in the to-be connectivity design.
+
+**Where "inside" is decided: told, not worked out.** The first correction had the proxy work it out
+for itself — the mesh's range from an environment variable the catalogue wrote, and the machine's
+container bridges from its own interfaces. That was a second definition of "the mesh", kept by one
+module beside the one the controller already has: it resolves "from the mesh" to every machine's
+address on the private network, and the packet filter is rendered from that list. Reviewed, it was
+replaced: [ADR 0167](../../02-DECISIONS/0167-a-membership-carries-what-its-module-receives-and-who-the-mesh-is.md)
+has every membership on the bus carry what its module receives and that list, and the proxy follows
+its membership. One composition, read by the filter and by the proxy.
+
+The proxy reads the source address, where the guard reads the interface, because it cannot see the
+interface a request arrived on. A claimed source does not carry here: a connection needs its replies,
+and replies to a mesh address leave by the tunnel.
+
+**What changed with it.** The internal name of a route that also has a public one is now served to the
+mesh only, like any other internal name. Outsiders have the public name, so nothing they could reach is
+lost. A container calling its own machine's internal name arrives from its container network and is
+refused; whether the mesh should issue those networks too is left open in ADR 0167.
+
+**Order of release.**
+
+1. The catalogue change, which gives the proxy a bus account. A machine running the proxy is not
+   composed until its account is issued, so the account is issued straight after
+   (`module issue route-proxy --node <machine>`), and then the machine is pushed.
+2. The controller and proxy change. The push after it publishes memberships that carry the routes and
+   the mesh, and each proxy takes them. Until then, a proxy serves its file, and internal names to its
+   own machine alone.