jochen
aad92ea8fe
The design pass. Everything a module needs is a requirement: a name, a contract, and one of four kinds of provider — a module, the node's host, the mesh, the operator. Installing a module resolves every requirement or refuses, naming everything missing at once. It retires six mechanisms that grew separately: provisions through bindings, settings, assigned ports, machine facts, minted secrets and literals in the definition. ADR 0113, proposed: a provider makes what it provides, and the mesh carries it back sealed to the consumer's node. It is the return path ADR 0048 left "to a separate decision", now needed three ways: data provisions with nothing to answer with, contracts needing a value the controller cannot make, and a vault that generates nothing. Who a consumer is stays the mesh's (ADR 0049). Genesis is the one exception. On acceptance it supersedes 0048 and amends 0085. ADR 0112 is revised from three sources to that single concept. ADR 0110 is amended for two points raised in review. The vault gets the mesh-vault seat (issue 106). A seat's holder outranks co-location for a provision it delivers. Writing that down exposed an inconsistency: mesh-store delivering postgres-database would have sent every database consumer to the control-node, against to-be 23's node-local stores. So a seat delivers a provision only where the mesh has one answer for everyone — artifact store, npm registry, git, vault — and mesh-store and mesh-broker deliver nothing. 23 and 26 follow. 'Control plane' becomes 'controller' in the records written today.
136 lines
7.1 KiB
Markdown
136 lines
7.1 KiB
Markdown
---
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layer: to-be
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status: in-progress
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code:
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- mesh-controller internal/catalogue/seats.go
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- mesh-controller internal/catalogue/resolve.go
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- mesh-controller cmd/mesh-controller/seats.go
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- mesh-controller cmd/mesh-controller/source.go
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- mesh-controller internal/inventory/migrations/0032-a-source-may-live-on-a-seat.sql
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- mesh-catalog modules/gitea/module.json
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updated: 2026-09-25
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decisions:
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- 02-DECISIONS/0110-a-seat-is-a-module-assignment-from-a-closed-set.md
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- 02-DECISIONS/0111-a-build-source-is-on-the-git-seat-or-external.md
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- 02-DECISIONS/0109-a-package-registry-seat-is-one-per-ecosystem.md
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---
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# 26 — The seats
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**What a mesh can have one of, and who fills each.** A seat is a named role at a scope, taken by a
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module assignment. The mesh defines which seats exist. Occupying one may deliver a provision, and the
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list of seats with their holders is the quickest answer to "what is in this mesh".
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## What a seat is
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A seat has four properties, fixed by the mesh rather than by any module:
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| property | is |
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|---|---|
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| name | what a manifest claims, and what a person reads in the list |
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| scope | node, site or mesh: where there may be only one holder |
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| delivers | the provision its holder answers for, or nothing |
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| decision | the record that made it a seat |
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**A module assignment holds a seat by claiming it.** The claim is the manifest's `claims`, and it is
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satisfied by assigning the module somewhere. The seat is not a second record beside the assignment.
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It points at the assignment, and everything the mesh knows about the holder is what it knows about
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that assignment: the node, the node's settings for the module, and what the module serves.
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**The set is closed.** A claim naming a seat the mesh does not define is refused, and so is a claim at
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the wrong scope. Adding a seat is a decision, recorded, for the reason every addition to the host's
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vocabulary is one: the set is what a person reads to learn what a mesh can have, and an entry nobody
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argued for is an entry nobody can explain.
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## The set
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| seat | scope | delivers | typically held by |
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|---|---|---|---|
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| `mesh-controller` | mesh | — | the controller |
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| `mesh-store` | mesh | — | the foundation's store |
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| `mesh-broker` | mesh | — | the foundation's broker |
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| `mesh-vault` | mesh | `secret` | the vault |
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| `the-artifact-store` | mesh | `artifact-store` | the artifact registry |
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| `the-catalogue` | mesh | — | the catalogue |
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| `npm-package-registry` | mesh | `npm-package-registry` | the forge |
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| `git` | mesh | `git` | the forge |
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| `the-build-machine` | node | — | a builder |
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| `the-dns-port` | node | — | the local resolver |
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| `the-intrusion-prevention` | node | — | an intrusion-prevention service |
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| `the-packet-filter` | node | — | the packet filter |
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| `the-private-network` | node | — | the private network the mesh runs over |
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| `the-resolver-configuration` | node | — | whichever of the alternative resolver configurations is chosen |
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| `the-showcase` | node | — | the showcase module |
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The controller holds this set in code, and a test asserts both its size and that every entry names
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the record that made it a seat. This document follows the code, not the reverse. If the two disagree,
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the test has been changed without this table, and the table is what is wrong.
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## A seat that delivers a provision
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A seat that delivers a provision may only be held by a module that provides it, at the seat's scope.
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A mesh seat delivers a mesh-scoped provision.
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**A seat delivers a provision only where the mesh has one answer for everyone.** The artifact store,
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the npm registry, git and the vault are each one per mesh by decision. The store and the broker are
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not: nodes run their own stores and a consumer uses the one on its machine
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([23 — Choosing a provider](23-choosing-a-provider.md)). So their seats guard that the foundation's
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own server is singular, and route nobody.
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**Its holder answers for that provision.** A requirement for it resolves, in order, to:
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1. the provider the consumer's node was pinned to, because a consumer coupled to one provider's
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contents has said so ([23 — Choosing a provider](23-choosing-a-provider.md));
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2. the holder of the seat, **even when another provider runs on the consumer's own machine**;
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3. otherwise nothing, and the requirement is refused, naming the unheld seat.
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Co-location, which answers first for every other provision, does not apply here: a seat says which
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one is the mesh's, and co-location answering first would let any second provider on a consumer's
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machine take over for that consumer, silently. So a second provider can run beside the holder and
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harm nothing. The forge holds
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`npm-package-registry`. An npm proxy may provide the same provision on another machine, and a module
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requiring an npm registry is still served by the forge, without anybody pinning it. Moving the role
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to the proxy is moving the seat: unassign the claim from one, assign it to the other, and every
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consumer follows.
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**What a consumer receives is a grant**, the same as for any provision: where the provider answers,
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what it serves, and a credential where one is minted. A consumer never reads the seat directly. The
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one exception is the controller itself, which reaches the store and the broker through a narrow
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seat placeholder because it made them before any module existed and cannot be their consumer.
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## A seat that delivers nothing
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Most node seats deliver nothing. They say which module is this machine's packet filter, or which of
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two alternative resolver configurations it runs, and a second holder is refused. That is the whole of
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their job, and it is a real one: it is the mesh saying what a machine is, in words a person can read.
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## The overview
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The controller lists every seat in the set with its scope, what it delivers, and each holder as a
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node and a module. A seat nobody holds is listed as unheld. That is an answer, "this mesh has no
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forge", and not a fault.
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Holdings are derived from assignments whenever they are asked for, never stored. The list is always
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what the mesh is running, because it is computed from the same thing that decides what the mesh runs.
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## The git seat, and where a build comes from
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A module is built from a repository, a path and a ref. The repository is one of two things, and the
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mesh records which:
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| form | means | recorded as |
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| on the `git` seat | a repository on the forge that holds the seat | its path on the forge, and the seat |
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| external | a repository anywhere else, a public forge for instance | its URL, exactly as given |
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For a repository on the seat, the controller composes the clone URL at the moment of building,
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from where the holder runs and the scheme and port it serves for `git`. The recorded source never
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contains an address, so moving the forge changes nothing that was recorded. The build machine is not
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told the difference: it receives a URL either way.
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With the seat unheld, a build from the seat is refused and says why. External builds carry on.
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**Not yet designed:** a credential for cloning a private repository. The mesh's own repositories are
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public. The natural place for a clone credential is the `git` provision's grant, and that is a
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decision still to take.
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