jschoubben
9f6aa7ea9c
Two things. A paragraph from the superseded 0117 survived beside the 0119 correction that reversed it, so §5 said both that the amqp interface retires and that it does not. The stale one is gone. And the framing. §1 opened with "the bus carries five kinds of traffic today, and this design keeps the five", with a column mapping each to the queue it used to be — which describes the mesh's nervous system as a port of something that did a fraction of this. It now says what the bus is: a role addressable without knowing its holder, the mesh's own state, work that queues until somebody can do it, and permissions derived from what a module declared. Conditions, observation and a person's client land there too as they are built. Glossary gains `bus` and `the deprecated broker`, with a note on why not to say "compatibility broker" or name it after a protocol — the second invites exactly the backwards framing this commit removes.
83 lines
6.0 KiB
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83 lines
6.0 KiB
Markdown
# Glossary — the words this repository uses, and the ones it stopped using
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One name per thing. This page is the authority; where an older record says something else, that
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record is being superseded, not this page. It exists because the terms kept drifting in
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conversation — control plane / controller / master / hub for one thing, substrate / foundation for
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another — and a mesh you cannot name precisely is a mesh two people describe differently.
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## The mesh and its machines
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- **node** — a machine in the mesh. There are 0..n of them, and each runs the host agent. A node is
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just a machine that has joined; being one implies nothing about what it runs.
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- **control-node** — the one node that also holds the `mesh-controller` seat. There is exactly one
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per mesh. "control-node" is not a separate kind of machine — it is a node that additionally runs
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the controller (and, today, the foundation). Lose it and the other nodes keep running what they
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were last told; they simply cannot be told anything new.
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- ~~master / slave~~, ~~hub / peer~~ — not used. The relationship is *controller and nodes*, and no
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node is subordinate: a node applies declarations on its own and survives the control-node dying.
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## What runs the mesh
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- **controller** — the component that decides what each node should be, holds the mesh's records,
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and tells nodes over the broker. Replaces **"control plane"** (borrowed from networking's
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control-plane/data-plane, and opaque here).
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- **mesh-controller** — the module that runs the controller. It **claims** the `mesh-controller`
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seat at mesh scope, which is what makes it singular. Replaces the module name **`mesh-control`**.
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(The git repository has been renamed `mesh-control` -> `mesh-controller` on the forge; the module,
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container and image it produces are `mesh-controller`.)
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- **foundation** — the store and the broker, raised at genesis before any module system exists.
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Replaces **"substrate"** (a biology metaphor that landed for no one). The foundation is not a
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third thing beside the store and broker — it *is* those two, named together.
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- **store** — the one postgres server. It holds the controller's own context databases
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(`inventory`, `identity`, `licences` — a context owns its store, [ADR 0008](../02-DECISIONS/0008-a-context-owns-its-store.md))
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and every module's own database. One server, many databases — never one shared "mesh database".
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- **bus** — the mesh's own nervous system: NATS, one per mesh, carrying every link the mesh has —
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control, declarations, builds, events, tool calls
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([ADR 0106](../02-DECISIONS/0106-the-bus-is-nats.md)). A module reaches it by requiring
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`mesh-bus` ([ADR 0120](../02-DECISIONS/0120-the-mesh-bus-is-required-not-ambient.md)); one that
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does not require it has no account on it. Held by the `mesh-broker` seat, which is named after
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the *role* rather than the server, so the server can change without the seat doing so.
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- **the deprecated broker** — the lavinmq module. It was the mesh's bus and is not any more. It
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keeps running as an **ordinary provider** of the `amqp` provision, for modules that need a
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message broker of their own the way something needs a database
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([ADR 0119](../02-DECISIONS/0119-amqp-is-a-provision-not-the-bus.md)) — no seat, not foundation,
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never raised at genesis, and a mesh that never installs it is complete.
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Say *the deprecated broker*, not "the compatibility broker" (it serves the mesh's own modules,
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not only the predecessor's) and not "the AMQP broker" (naming it after a protocol invites
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describing the bus by contrast with it, which is backwards: the bus is the mesh's nervous
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system and this is a module).
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## What the mesh stores and serves
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- **package** — what code resolves when it is **compiled**: an npm/cargo/pypi dependency, by
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**version**. Served by the **package-registry** (gitea). Only a builder talks to it.
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- **artifact** — what the mesh delivers to a machine to **install and run**: an OCI image, by
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**digest**. Served by the **artifact-store** (distribution). Every node pulls from it.
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- These are two protocols, not one store being weak — see [ADR 0075](../02-DECISIONS/0075-two-stores-and-which-provides-what.md).
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## How modules relate to the mesh
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- **seat** — a named role at a scope (node / site / mesh), held by a module assignment, from a
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**closed set** the mesh defines: a claim naming a seat outside the set is refused. A seat may
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**deliver a provision**, and its holder is then the mesh's answer for it when several modules
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provide it ([ADR 0118](../02-DECISIONS/0118-a-module-declares-its-own-seats.md) (superseding [ADR 0110](../02-DECISIONS/0110-a-seat-is-a-module-assignment-from-a-closed-set.md))).
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The set, with who holds each seat, is the overview of what a mesh has
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([26 — The seats](../03-DESIGN/01-to-be/26-the-seats.md)). A seat has a **capacity**: a
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capacity-1 seat is exclusive (one holder); a higher-capacity seat is a **bench** (several holders
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coexist).
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- **claim** — a module taking a spot on a seat. `claims: [{name, scope}]` in a manifest. A
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mesh-scoped exclusive claim is how the mesh says "there is one of me". A foundation seat is
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named after the server it guards: the `mesh-controller`, `postgres` and `lavinmq` modules claim
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the `mesh-controller`, `mesh-store` and `mesh-broker` seats ([ADR 0079](../02-DECISIONS/0079-the-foundation-seats-are-named-after-their-servers.md)).
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- **provision** — a service one module `provides` and others `require`; the mesh resolves a provider
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and wires the two with an endpoint and a credential. A provision is a service you offer, a seat
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is a role you occupy, and the two meet where a seat delivers a provision: occupying the seat is
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what makes a module *the* provider of it.
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## How this page is kept
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A new name for an existing thing lands here first, in the same change that introduces it in code. A
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record under `02-DECISIONS/` keeps whatever word it was written with — those are immutable — so a
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term retired here may still appear there, and the mapping above is how to read it.
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