mesh-control

Tier 2 of Novox Mesh — the control plane. Everything that needs to know about more than one node.

That is the whole test, and it draws the line the host cannot: the host applies and does not decide, because deciding needs knowledge one machine does not have. Which nodes should run the store, which peers belong in an overlay, whether a node has been unreachable for a week — nobody on a single machine can answer any of them.

The reasoning lives in novox/hq; this repository carries no argument that is not settled there.

What it is not

• Not the thing that changes machines. It decides; the host applies. It never reaches into a node except through the host, over the link, in a bounded vocabulary.
• Not a database. There is no mesh database. Each context owns its own store and nothing outside a context touches it — including nodes, which hold no credential to any of them.
• Not privileged. It has no more access to a machine than a declaration can express.

What exists today

One context of seven, and one of the things it will do.

inventory	node records and enrolment tokens — built, as far as identity
identity	the control plane's signing key, and the keys nodes are known by — built
config, connectivity, provisioning, delivery, observability	not built
the interface every surface speaks to	not built; its shape is not decided

mesh-control migrate                    bring each context's schema up to date
mesh-control node add <name>            create a node record
mesh-control node list                  the nodes this mesh knows about
mesh-control token issue --node <name>  a one-time right to join, for an existing record
mesh-control token issue --new <name>   create the record and issue for it
mesh-control identity show              this control plane's signing key
mesh-control broker show                where the broker is, and what to expect there
mesh-control version                    what this binary is

migrate is step 3 of the substrate bootstrap — the step the first node cannot get past, run against a database raised moments earlier from the bundle the host carries.

Tokens, and what they are missing

A token is a one-time right to join, issued for a node record — which is where re-enrolment is decided, since what an identity binds to is settled when the token is made rather than when it is presented.

What is built: the secret is 256 bits from the system's random source, shown once, and stored only as a hash, so a copy of this database is not a set of working credentials. It is usable exactly once and only before it expires, and both are read from the row rather than from a status something would have had to write. Issuing again for the same node invalidates the outstanding one — two live tokens are two machines able to join as the same node.

Redemption is a single statement that both finds a live token and spends it, so eight concurrent attempts on one secret produce exactly one winner. There is a test that runs them.

A token now carries three of its four parts, and is one line of base64 a person can copy. The signing key is real: an Ed25519 key this control plane generates once and keeps, whose public half travels in every token. A node believes a declaration because it carries a signature that key made — and pinning only the broker would not do, because it would make the control plane's authority transitive, so a compromised broker could forge declarations, and since the host applies whatever the link delivers that is the whole machine.

All four parts are built. Given MESH_BROKER_ADDRESS and MESH_BROKER_CERTIFICATE, a token carries everything ADR 0004 requires. Without them it carries two, and token issue prints it and names what is missing rather than producing something that looks complete and cannot be used.

The fingerprint is derived from the certificate, never configured. A configured one can drift from the certificate it describes, and a drifted pin is worse than none: every node issued a token during the drift refuses to connect, and the failure looks like an attack. It is computed over the DER bytes — what a client actually sees on the wire — so the same certificate re-wrapped with different line endings still produces the same pin.

Two contexts, and the rule between them is real

identity is the second context and it exists partly to test a claim this repository had made and never checked: that a context reaches only its own store. It holds MESH_STORE_IDENTITY; inventory holds MESH_STORE_INVENTORY; there is no setting that reaches both and no way to ask for one. Run migrate with only one and it stops, naming the grant it does not have.

A token needs a node record from one and a signing key from the other. Neither reads the other's store — the process holding both grants asks each for its part.

How a node is known

The node generates a keypair; the mesh records the public half. The same principle as SSH, and the same rule 08-connectivity already applies to the overlay keys — which is where this was settled all along, though it took being asked directly to notice.

Only the public half is ever stored, and that is the property worth having: a copy of this database grants nothing. It is a list of who to believe, not a set of credentials, which is what makes compromise of a node is compromise of that node literally true.

Exactly one key is live per node. Re-enrolment revokes the one it replaced, in the same transaction — two live identities for one node record is the stolen-laptop case, with the replaced machine still believed. The database enforces it as well as the code, and there is a test running six concurrent enrolments that fails when the constraint is removed.

Not the machine's SSH host key, though that was the obvious economy. Host keys are regenerated by reinstalls and image clones, which would silently un-enrol a node; their lifecycle belongs to sshd rather than the mesh; and a partial host has no SSH daemon at all.

Reaching a store

A context is granted only what it exclusively owns. No shared writes, no read-only role on another context's store, and no connection string that reaches more than one.

That is a rule about credentials, so it is built as one. There is no mesh-wide connection setting and no way to ask for one:

MESH_STORE_INVENTORY=postgres://…/inventory

A process granted inventory holds that variable and no other. Reaching another context's store is not a matter of restraint — it has no address for it and no credential to present. And it is how the rule is checked: what a context can reach is visible in the declaration that runs it, as the list of variables it was given.

Each context's database is named after the context. There is deliberately no database named for the mesh as a whole.

Migrations

Numbered, embedded in the binary, applied in order, each in a transaction with the row recording it. The applying is four lines; the rest is refusals, and the refusals are the point:

it stops when	because
a migration that ran has since been edited	the database holds the old version, the repository holds the new one, and nothing holds the difference
a migration is numbered below one that already ran	usually two branches taking the same next number — applying it now runs the schema in an order nobody tested
two migrations share a number	order is the entire guarantee, and two files with one number have none
a file in the directory is not a valid migration name	a misnamed migration would otherwise never run and nothing would say so
a migration is empty	it records that something happened and changes nothing, which cannot be told from a mistake

All of them stop rather than warn. At the moment any of them is true, nobody knows what the database contains, and there is no correct guess about a schema.

Running it again does nothing. Two copies running at once take an advisory lock, so a restart during a slow migration does not become two runners racing.

Building

make build      the binary
make image      the container image
make check      gofmt, vet, and every test against a real PostgreSQL

make check raises a throwaway PostgreSQL in a container and takes it down afterwards, including when the tests fail. Without one the tests that need a database skip and say so rather than passing quietly — make test is the honest subset, not the gate.

Tests run against a real database rather than a fake because what is being tested is the database's behaviour: that DDL is transactional, that an advisory lock serialises, that a checksum mismatch is caught against a record PostgreSQL actually kept. A fake would assert that the fake behaves as expected.

Every test here has been confirmed to fail when the behaviour it defends is removed. Two did not, when first written, and both are now commented with what they were missing.

The image

FROM scratch, holding one statically linked binary and nothing else — no shell, no package manager, no libc, no CA certificates.

Not a size optimisation. The bundle a host carries pins this image by digest, and it is fetched and run on a machine where no mesh exists to check anything and a person is expected to have read the bundle and believed it. Everything in the image is something that person would have to audit.

Where the reasoning lives

what the control plane is	novox/hq ADR 0006
what it takes to run one, and why Go	novox/hq ADR 0006
a context owns its store, exclusively	novox/hq ADR 0008
schema changes are numbered migrations	novox/hq ADR 0013
a test defends a decision	novox/hq ADR 0017