jschoubben
92e8c74ce4
Building tier 0 forced the question "the one binary installed by hand" had been carrying unexamined. A TypeScript host needs a runtime present before it runs, so the thing installed by hand becomes two — and the second must be installed by the means the host exists to replace. So the host is a statically linked binary that requires nothing present, written in Go. Rejected: a runtime installed first, which breaks the property the tier rests on; and bundling the runtime into the executable, which carries ninety megabytes to preserve a language choice and puts a young feature at the bottom of the stack. The argument that decided it is architectural rather than about taste. 0037 means the host never queries the mesh database and 0039 means it only receives declarations, so the host shares NO code with any other tier — not a client, not a schema, not the SDK. The language boundary falls exactly on a boundary that already exists, and a second language usually costs duplicated logic where here there is none to duplicate. §8 gains a scope: it said "TypeScript throughout" when everything was a service or a surface, and is now scoped to those with tier 0 named. Another sync owed. Playbook 04 steps 2 and 4: repos.md records mesh-host as existing, the design takes code: [mesh-host] and status: in-progress.
9.4 KiB
layer, status, code, updated, decisions
| layer | status | code | updated | decisions | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| to-be | in-progress |
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2026-08-26 |
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The node host
Tier 0. The one thing ever installed by hand, and the only thing that changes a machine.
What it is
A statically linked binary that requires nothing to be present — copy it onto a machine and run it, and that is the whole installation (ADR 0041). Written in Go, because the job is system-level and because the host shares no code with any other tier.
A single binary with one job: apply declared state on this machine (ADR 0037). Overlay membership, packet filtering, packages, services, containers and filesystems are not six concerns it carries; they are six instances of the one.
It replaces three things that exist today
(00-as-is/05): the three hand-run bootstrap
scripts — first node, joining, rescue — and the synchronisers that rewrite managed files
(00-as-is/06).
What it is not: it does not decide anything that needs another node, it never queries the mesh database, and it has no listening surface.
The parts
| Part | Owns |
|---|---|
apply |
reconciling declared state on this machine |
store |
local state, authoritative while disconnected |
link |
the single outbound connection to the control plane |
profile |
what this machine can be asked to do |
inventory |
what this machine is and has |
substrate.lock |
the pinned tier-1 descriptor, appliable with no mesh present |
apply
Takes a declaration and makes the machine match it. Idempotent: applying the same declaration twice changes nothing the second time, and applying it to a drifted machine returns it.
Three properties, each following a recorded decision:
A failed step fails the apply. Not "logs and continues" (ADR 0008). A partial apply that reports success is the mesh's most expensive shape.
Each applier reads back. Setting a value is not evidence the value took. The firewall is
asked whether the rule loaded; conntrack is asked what timeout it holds. This is how-we-build
§5 as a component requirement rather than a review habit.
What was applied is recorded after it works, never before (ADR 0035). A failed apply leaves the machine in whatever state it reached, and nothing must claim otherwise.
store
Local, and authoritative while disconnected. Not a cache of the control plane — the record of what this node has applied and what it currently holds.
This is structural rather than convenient: if disconnection is an ordinary situation rather than an exception (ADR 0036), the store is what makes it ordinary. A laptop shut for a week comes back and reconciles; it does not come back and ask what it is.
link
The node's one connection to the control plane, and its security boundary (ADR 0039).
It is the broker connection that already exists (ADR 0001) — outbound, node-initiated, per-node addressed — carrying per-node identity instead of a shared credential. The node owns no password. It owns an identity, and that identity is what it presents.
What arrives is bounded by form: declarations of known shape, never a command to run.
It must fail legibly. A node that cannot link says which side refused and on what grounds. A boundary that refuses without saying why is worse than the password it replaced.
profile
What this machine can be asked to do — a graphical session, a container runtime, an architecture, a network position.
Detected, never assumed. A package being installed does not mean a capability is present (04-ISSUES/007): a capability is real when it is present, running and working, and the difference is the whole point of detecting it.
The profile is what makes ADR 0036 work: a node is a node, and what varies between them is here rather than in the definition.
inventory
What this machine is — its identity, what it holds, what it has applied. Reported upward over the link; never asked downward.
Where a declaration comes from
One behaviour, two sources (ADR 0038):
| Situation | Source |
|---|---|
| no mesh reachable | substrate.lock — the pinned bundle the host carries |
| mesh reachable | the control plane, over the link |
The first node is not a different kind of node. It is a node whose mesh is not up yet. It applies the bundle it carries, the control plane comes up on top of it, and from that moment it takes declarations like every other node. Its specialness is temporary and self-erasing.
A joining node does the minimum to be reachable and nothing else — an identity, an address, one peer — and then stops deciding. It does not compute the overlay; it needs one peer to reach the mesh, and the full peer set arrives derived.
What a declaration is
Open, and the first thing to settle in build. The shape is constrained but not chosen:
- It is data, not instructions — the host's vocabulary is finite, versioned and auditable, and anything outside it is refused rather than best-effort interpreted.
- It is per-node and complete: what this machine should be, not a delta against what it was. A delta requires the sender to know what the receiver holds, which is the coupling the store exists to remove.
- Every addition to the vocabulary widens what a compromised control plane can express, so it is a security artefact and additions are reviewed as such.
Build order
Staged so each stage is verifiable in the lab before the next exists.
1 — profile and inventory. The host runs on a machine, detects what it can do, and reports
what it is. No control plane, no declarations, no network. Verifiable immediately: the lab's
place: gains its first implementation, and a raised scenario finally contains something.
2 — apply, from the bundle. The host applies substrate.lock with no mesh present. This is
the first node's path, and it is the claim the skeleton's Move 1 rests on and has never proved:
that one host can raise the substrate alone.
3 — link and store. The node connects, receives declarations, and holds what it applied.
4 — enrolment. The one genuinely new mechanism in ADR 0039; everything else there is configuration of what already runs.
Stage 1 is deliberately the smallest useful thing. The lab currently raises empty machines
(00-as-is/11) because place: has nothing to place; stage 1 ends
that, and every later stage is tested by a lab that already works.
How it is verified
The lab is the harness. A scenario places a host on a machine and asserts what it did — against a real hypervisor, with the boundary never mocked (ADR 0034).
Each decision above owes a test:
| Decision | What asserts it |
|---|---|
| 0037 — the host never queries the mesh database | no database client in the dependency tree; a dependency-direction lint failing on an upward import |
| 0038 — one behaviour, two sources | the same code path raises a first node and joins a second |
| 0039 — a node holds no shared credential | a raised node's store contains no credential to any service |
| 0036 — disconnection is a situation | a node cut off and returned reconciles without being re-adopted |
| 0008 — a failed step fails the apply | an apply with a failing step reports failure |
Open
- What a declaration is. Above; the first thing to settle.
- Whether one host can raise the substrate alone. Move 1 assumes it. Stage 2 tests it, and if it is false the tier boundary moves.
- What the host carries versus what it finds. It manages
wg,nft,pacman,docker; it does not contain them, and how it obtains one it lacks is undecided — 04-ISSUES/007. - Six vocabularies. Zero dependencies, but the host must still know what a peer, a rule, a
package, a unit, a container and a dataset are. Nothing has measured that surface, and it is
the residue of the question
host-size.mdanswered. - Rescue. ADR 0038 suggests it is a node whose local state is discarded so the mesh re-derives it, and does not decide it.
- What may expire. An identity needing refresh to stay valid would make a laptop fail for being a laptop (ADR 0036).