ADR 0169 accepted; design 08's join order starts with the tunnel

2026-10-02 13:17:32 +02:00
3 changed files with 25 additions and 2 deletions
@@ -1,6 +1,6 @@
 ---
 topic: the mesh
-status: proposed
+status: accepted
 date: 2026-10-02
 deciders: jochen
 reconstructed: false
@@ -179,7 +179,7 @@ python3 00-META/checks/index.py            fail if stale
 - **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)
 - **0168** — [A converged machine is filtered by the mesh alone, and the host says what else refuses](0168-a-converged-machine-is-filtered-by-the-mesh-alone.md)
- **0169** — [A machine joins through the tunnel, and the bus is never public](0169-a-machine-joins-through-the-tunnel-and-the-bus-is-never-public.md)  *(proposed)*
+- **0169** — [A machine joins through the tunnel, and the bus is never public](0169-a-machine-joins-through-the-tunnel-and-the-bus-is-never-public.md)

 ### Its tiers, from the bottom up

@@ -9,6 +9,7 @@ code:
  - mesh-host internal/apply (the service that reflects a rule set)
 updated: 2026-10-02
 decisions:
+  - 02-DECISIONS/0169-a-machine-joins-through-the-tunnel-and-the-bus-is-never-public.md
  - 02-DECISIONS/0168-a-converged-machine-is-filtered-by-the-mesh-alone.md
  - 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
@@ -173,6 +174,28 @@ the broker's node must be dialable by every node, at a stable address, and so mu
 reachable; on one network it does not. A mesh whose nodes are all behind NAT cannot be raised, and
 a broker node whose address moves invalidates every token issued for it.

+*2026-10-02.* **The order changes at step 1: the tunnel comes first, from the token**
+([ADR 0169](../../02-DECISIONS/0169-a-machine-joins-through-the-tunnel-and-the-bus-is-never-public.md)).
+The circularity above is real, and it is broken differently. The overlay is configured by the mesh,
+except for the one peer a joining machine needs, and the token carries that peer. So the sequence
+becomes:
+
+```
+0  the node has an underlay address     the machine's own
+1  the node makes its tunnel key        before any token; it prints the public half
+2  a token is issued for that key       its address assigned, and the hub sent it as a peer
+3  the tunnel comes up to the hub       from the token alone: the hub's endpoint and key, its address
+4  the node dials the bus               OVER THE TUNNEL, at the bus's private address
+5  it proves itself, and is proved to   enrolment, checking the key is the one the token named
+6  the rest of the overlay              the whole peer set, delivered as files
+7  names, filtering, routes             as before
+```
+
+The link no longer stays on the underlay. The bus is reached over the tunnel by every machine,
+including one that is joining, so it is never opened to the internet. The precondition becomes: **the
+hub's tunnel must be dialable by every node, at a stable address.** That port answers nothing to a
+key it does not know.
+
 **Whether the link should later move onto the overlay, with the underlay as fallback, is
 [open](../../02-DECISIONS/0007-connectivity.md).** It is a decision rather than a derivation: the
 gain is which network carries bytes, not what an attacker can reach, since the link is already