---
layer: to-be
status: in-progress
code:
  - mesh-controller internal/catalogue/filtering.go
  - mesh-controller examples/route-proxy
  - mesh-controller internal/identity/authority.go
  - mesh-host internal/identity/serving.go
  - mesh-host internal/apply (the service that reflects a rule set)
updated: 2026-09-27
decisions:
  - 02-DECISIONS/0104-a-provision-may-be-answered-by-an-adapter-to-the-predecessor.md
  - 02-DECISIONS/0106-the-bus-is-nats.md
  - 02-DECISIONS/0105-the-mesh-adopts-the-predecessors-tunnel-in-place.md
  - 02-DECISIONS/0119-a-taken-tunnels-predecessor-is-retired.md
  - 02-DECISIONS/0108-a-route-carries-the-policy-applied-to-a-request.md
  - 02-DECISIONS/0103-what-an-adopted-node-holds-and-what-its-guard-refuses.md
  - 02-DECISIONS/0100-a-node-in-use-is-adopted-before-it-is-converged.md
  - 02-DECISIONS/0099-a-step-that-runs-once-names-what-it-reads.md
  - 02-DECISIONS/0098-a-fact-a-provider-makes-at-first-start-is-fetched-from-it.md
  - 02-DECISIONS/0005-the-node-host.md
  - 02-DECISIONS/0004-a-node-and-how-it-joins.md
  - 02-DECISIONS/0007-connectivity.md
  - 02-DECISIONS/0007-connectivity.md
  - 02-DECISIONS/0004-a-node-and-how-it-joins.md
  - 02-DECISIONS/0007-connectivity.md
  - 02-DECISIONS/0006-the-substrate-and-the-control-plane.md
  - 02-DECISIONS/0066-public-routing-is-name-agnostic.md
  - 02-DECISIONS/0029-a-network-is-a-shape-because-an-action-cannot-be-undone.md
  - 02-DECISIONS/0044-a-public-name-is-provisioned-like-any-capability.md
  - 02-DECISIONS/0045-a-machine-firewall-is-the-sum-of-what-it-listens-on.md
---

# Connectivity

One of [the controller's](06-the-controller.md) ten contexts, and the one with the most
moving parts: **overlay, resolution, exposure, filtering, certificates.**

It is written as a whole because the five are one design. They share inputs, they must agree, and
every one of them today is computed in a different place by a different module from a different
copy of the same facts.

## Why it is controller work

Apply [the test](06-the-controller.md) — *everything that needs to know about more than one
node* — to each responsibility:

| | needs to know | whose |
|---|---|---|
| **overlay** — who peers with whom, at what address | **every node**, and which of them can be dialled | controller |
| **resolution** — which name is which node | **every node** | controller |
| **exposure** — which public name reaches which container | **which node is publicly reachable** ([ADR 0007](../../02-DECISIONS/0007-connectivity.md)) | controller |
| **filtering** — which port is open, to whom | what is assigned here, and the overlay's shape | controller decides, host applies |
| **certificates** — who may present which name | which name belongs to which node | controller |

**Not one of the five can be answered by a machine on its own.** That is the whole reason this is
a context rather than a set of node-local modules — and it is exactly what the current
arrangement gets wrong, by computing all five on the node from a direct database connection.

## The shape: decided centrally, delivered as files

Every one of the five resolves the same way, and it is worth stating once rather than five times:

> **The connectivity context computes the configuration. It arrives over the link as `file`
> resources. The service reads files and knows nothing about the mesh.**

This costs **no new host vocabulary**. `file`, `directory`, `service` and `container` already
exist; WireGuard, the resolver and the proxy are all *a container or a package, plus files*.

It is also what removes the last two upward dependencies.
[Research 006](../../01-RESEARCH/006-mesh-from-scratch/host-size.md) counted exactly two modules
opening a direct connection to the controller's database — `wireguard` and `traefik` — and
they are the reason every node permanently holds a credential to it
([ADR 0004](../../02-DECISIONS/0004-a-node-and-how-it-joins.md)). Both are connectivity
modules. **Closing this context closes that set.**

### And they are modules, not a second mechanism beside the module system

*Written 2026-08-29, from building it. The first version was code beside the module system doing
the module system's job, and the fault it produced is the point of writing this down.*

**A machine was on the private network because it had an address.** Every node that had been
placed got a peer list, whether or not anybody wanted it there, and there was no way to say a
machine should stay off. That is what "special-cased" cost, and it was invisible until somebody
wanted the exception.

**What made it look unavoidable:** a peer list cannot be written in a manifest. It is derived from
every other machine, so it differs on each one and changes when any of them changes. So the
manifest says its resources are **computed** — it names something in the controller that works
them out per node — and it is a module in every other respect: assigned, resolved, configured by
settings, and absent from a machine nobody gave it to.

**What that made possible immediately** is the arrangement below, which the code has:

| module | provides | requires | claims |
|---|---|---|---|
| the WireGuard one | a private network, **and the mesh's own addressing** | | *the* private network, one per node |
| the names one | name resolution | the mesh's own addressing | |
| `networking` | | both of the above | |

**Three rather than one, because WireGuard is one VPN of several.** Naming the module after the
job — `networking` — and putting WireGuard inside it is the retired *flavor* idea wearing a
generic name: the second VPN has nowhere to go. So a module is named for what it *is* and declares
what it *does*, and `networking` is the third row — requirements and no files
([ADR 0009](../../02-DECISIONS/0009-modules-and-the-graph.md)).

**Names left the WireGuard module for their own.** They had been delivered inside it, on the
argument that a machine with peers and no names is half on the network. True, and the wrong place
to fix it — names are identical over a *different* private network, so bundling them made one
module out of two things. They require the mesh's **addressing** rather than a private network in
general, because that is what they are computed from: over a VPN that hands out its own addresses
the mesh has nothing to write, and refusing is what stops a machine being given a hosts file that
means nothing on it.

**And the claim is not decoration.** Choosing a different VPN still installed WireGuard — dragged
back in by the names, which needed addresses only WireGuard hands out — and nobody was told.
Running two VPNs is not always wrong; being *the* one the mesh runs over is singular. So it is a
claim, and the collision is refused by name.

**And the proxy's half, which was the other module reaching into the database.** A web application
requiring a reverse proxy has to say *which name, which port*, and there was nowhere to put it —
`requires` says a thing must exist and never said what to do with it. A module now contributes to
a requirement, the controller collects every contribution on a node, and the provider is given
them as a file at a path it named. It reloads when that file changes, by the same `restart-on` the
private network needed when a peer list changed under a running interface.

**The proxy's configuration is not written by the mesh.** It is given the facts and turns them
into whatever it runs, which is why swapping Traefik for something else touches nothing that
publishes through it. See [ADR 0009](../../02-DECISIONS/0009-modules-and-the-graph.md) for the
other direction — handing a credential *back* — which is the larger half and is not built.

**What is still not a module, and why that is correct.** The host needs none of this. It has an
address and a route before the mesh exists — that is the machine's own networking — and the
broker's address is carried in the token rather than resolved
([ADR 0004](../../02-DECISIONS/0004-a-node-and-how-it-joins.md)). **The one connection that
carries modules cannot itself be one.** Everything above it can be, and now is.

## The order it comes up in

The one thing to get right, because everything else depends on it:

```
0  the node has an underlay address     the machine's own — DHCP, or a provider gave it one
1  the node dials the mesh              OVER THE UNDERLAY, at the address in its token
2  it proves itself, and is proved to   the link exists      (ADR 0004, ADR 0004)
3  the mesh grants it an identity       and an overlay address
4  the overlay comes up                 peer graph delivered as files
5  names resolve                        resolver config delivered as files
6  filtering is applied                 derived from what is assigned here
7  routes and certificates              once this node has something to expose
```

**Step 1 runs on the underlay and never on the overlay.** This is the circularity that must not
be created: the overlay is configured by the mesh, so a link that required the overlay could
never be established on a new node. The link stays on the underlay permanently — it is
outbound-only and carries its own identity, so it needs nothing the overlay provides.

**Nothing before step 3 can resolve a mesh name**, which is why the token carries an *address*
([ADR 0004](../../02-DECISIONS/0004-a-node-and-how-it-joins.md)). Today this is
patched with an `/etc/hosts` floor written underneath the resolver; under this design there is
nothing to patch.

**Step 1 has a precondition this document treated as a fact to record rather than a requirement:
the broker's node must be dialable by every node, at a stable address, and so must the hub**
([ADR 0007](../../02-DECISIONS/0007-connectivity.md)). Across the internet that means publicly
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.

**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
encrypted against a pinned fingerprint.

## 1 — The overlay

**What is decided:** the peer graph. For every node: its overlay address, which peers it holds,
which of those it may dial, and which must dial it.

**Inputs, all declared:**

- **reachability** — an endpoint, or none
  ([ADR 0007](../../02-DECISIONS/0007-connectivity.md)). Not
  inferred from the address shape, which is wrong for carrier-grade NAT, wrong for IPv6, and
  wrong for a routable address behind a closed firewall.
- **site** — where the machine physically is, or nothing if it roams.
- **role** — hub or not, **declared**. Today it is inferred from an address prefix, which means a
  renumbering is an outage and nothing can be asked which node is the hub.

**Keys.** Each node generates its own keypair. **The private key never leaves the machine**; the
public key is published to the mesh. This is already true and it is already right — it is
[ADR 0004](../../02-DECISIONS/0004-a-node-and-how-it-joins.md)'s *a node holds its own
identity* applied to the overlay, and it means the controller computes a graph it cannot
itself impersonate.

**Shape: a hub, with direct peering between co-located nodes.**

| | |
|---|---|
| two nodes at the same site | peer **directly**, host-routed, with a keepalive |
| everything else | routes through the **hub** |
| a node with no site — it roams | **hub only** |

**Roaming is hub-only deliberately, and the reason is a property of WireGuard rather than a
preference: there is no failover.** A more specific route to a dead endpoint blackholes; it does
not fall back to the general one. So a node whose location changes gets exactly one path, because
two paths would mean one of them silently swallowing traffic.

**What the host receives:** an interface configuration and a peer list, as files. It does not
compute them, and after this it holds no credential to the mesh's database.

### Four things the lab found, none of them visible from the mesh's own state

*Written 2026-08-29, on the first three machines to actually run this.*

Each looked like a working network from every angle the mesh can see: the graph was right, the
files were right, the services were up, and every node reported success.

- **A running interface does not re-read its configuration.** A node joins, every existing node's
  peer list changes, each file is replaced — and the service is already running, so nothing
  reloads it. Every existing node keeps a network that no longer exists. The declaration has to
  say the service must *reflect* the file, which is declared state; a command to restart would be
  an action, and the link may not carry one
  ([ADR 0005](../../02-DECISIONS/0005-the-node-host.md)).
- **A hub that shares a site with a spoke was emitted twice** — once as a direct peer and once as
  the route of last resort. WireGuard takes one entry per public key, so the interface refuses the
  file. The ordinary shape of a small mesh, and in none of the tests written before it ran.
- **Two nodes at one site that neither can be dialled must not peer directly.** Nobody opens the
  path, and the direct route is more specific than the hub's, so it wins and blackholes. This
  document's own warning, arriving in its implementation: *a more specific route to a dead
  endpoint blackholes; it does not fall back to the general one.*
- **The container runtime closes the door the overlay needs.** Docker sets the FORWARD policy to
  DROP, so a hub with `ip_forward` enabled still carries nothing between its spokes. The foundation
  at tier 1 silently breaks the network at tier 2, and nothing in either tier's state says so. The
  hub inserts its own rule above those chains and removes it on the way down.

**The pattern in all four:** the mesh's picture of the network was correct and the network did not
work. That is the argument for the lab in one line — none of these is reachable by reasoning, and
each was found within minutes of a real machine trying it.

## 2 — Resolution

**Two name spaces, and they do not mix:**

| | resolves to | certified by |
|---|---|---|
| **internal names** | overlay addresses | the **mesh CA** |
| **public names** | whatever the outside world must reach | a **public authority** |

A node's mesh name is its overlay address. Its public name, if it has one, is a separate fact
used by things outside the mesh — and the separation carries two lessons that were learned
expensively enough to be worth restating:

- **Mesh names are not multicast names.** A name resolved by local multicast discovery introduces
  a delay and a failure mode that appears on one node and not others — the worst shape a fault
  can have.
- **A node must not pin its own public name locally.** The duplicate record breaks resolution of
  that name for everything else that needs it.

**What the host receives:** the resolver's configuration, as files, listing every peer's internal
name and overlay address.

**What goes away:** the `/etc/hosts` floor. It exists because a node had to reach the mesh
database before its own DNS existed; with [ADR 0004](../../02-DECISIONS/0004-a-node-and-how-it-joins.md)
nothing needs a name before the link, and a fallback nothing needs is a path nothing tests.

### Names, and what a container can see

*2026-08-31, from a container that could not resolve a name every machine could.*

Internal names are `<node>.internal` — the suffix is the one IANA reserved in 2024, so a name that
leaks into a public resolver fails rather than reaching a stranger's machine. They are computed
centrally, because a name set needs every node at once, and written to each machine's hosts file.

**A file rather than a resolver**, and the reasoning holds: it works on every Linux, needs no
package, and has no failure mode of its own. The stated trigger for a daemon was *names that are
not one-per-node* — service names, wildcards.

**But a container does not inherit the machine's names.** It gets its own hosts file holding only
its own hostname. So every name the mesh wrote was invisible to the majority of things that need
one — and *on the machine it always worked*, which is exactly what made it easy to miss. It was
found by a database client on one node failing to resolve another node, on a mesh where both names
were correct and present on both machines.

**So the mesh gives its names to the containers it declares**, written into each container's own
hosts file by the runtime. That extends the file decision rather than overturning it. Given by the
mesh and not chosen by a module: a module that listed the machines would go stale the day one
joins, and a module that did not would be one whose containers cannot reach anything by name.

**The boundary, which is deliberate and worth stating:** *declared* containers. A container
somebody starts by hand is not the mesh's to configure, and reaching into every container on a
machine — declared or not — is what a nameserver in `resolv.conf` would be for.

### The resolver, built

*2026-08-31.* **A service is reached at `<service>.<node>.internal`** — the first label is the
service, the rest is the node — so what resolves is *anything under a node's name*, going to that
node. What routes it once it arrives is a proxy's, and stays separate.

**The mesh writes the data and runs no daemon.** One wildcard per machine, from the same set that
writes the hosts file. A resolver is third-party software and runs *on* the mesh rather than being
*of* it: the mesh has no business shipping one, choosing which one, or knowing its configuration
language. Swapping dnsmasq for unbound changes that module and nothing in the controller.

**Two roles, two claims, because they are different things.** systemd-resolved cannot answer a
wildcard at all — it routes the mesh's suffix to something that can. Treating serving and asking
as one role produces a module that cannot work.

| | claims | |
|---|---|---|
| serving | `the-dns-port` | answers the wildcards |
| asking | `the-resolver-configuration` | decides what the machine asks |

So *which* resolver is not a mesh-wide decision. One machine can use what systemd already owns and
another can run dnsmasq, and two of either on one machine is refused rather than fought over.

**Two things a resolver must not do**, both found by a machine rather than by reasoning:

- **Take an address something else holds.** systemd-resolved holds `127.0.0.53` *and* `127.0.0.54`.
- **Read `resolv.conf` for its upstreams.** Whatever points a machine at the mesh writes the
  resolver's own address there, so it becomes its own upstream and every query it cannot answer
  loops until its receive queue fills. It needs no upstream: only the mesh's suffix is routed to
  it.

*Checked on two machines, through the path an application takes — nsswitch, files, then DNS —
because the module deciding what the machine asks is half of what is being tested and only that
path goes through it.*

**That is now the second reason to want a resolver**, and it is a different one from the trigger
above:

| | |
|---|---|
| names that are not one-per-node | a service named under a machine — `postgres.novox.internal` |
| containers the mesh did not declare | anything a person or another tool starts on a node |

### Which resolver is not a question the mesh answers

*Written 2026-08-31, after treating it as open when it had been decided two days earlier.*

**A resolver takes over `/etc/resolv.conf`, which is a singular resource, so it is a claim** —
[ADR 0009](../../02-DECISIONS/0009-modules-and-the-graph.md) lists it in the table beside the seat
and pid 1. Choosing between resolved, dnsmasq and unbound is **assigning a module**, per machine,
and two of them cannot both be assigned there:

> `resolved-config and dnsmasq both claim "/etc/resolv.conf", and only one thing may hold it per node`

So there is nothing global to settle and nothing for the mesh to guess. One machine can use what
systemd already owns and another can run dnsmasq, and neither has to know about the other.

**What the mesh contributes is the part only it can know**: which machines exist and where. That
is `mesh-resolver`, which writes one file and holds no claim, because writing a file takes nothing
over. A daemon module requires that data and claims the resolver — so swapping the daemon changes
that module and nothing else.

**This was recorded on 2026-08-29 and reopened as an unanswered question on the 31st.** Which is
the argument for the table in ADR 0009 being a table: the pattern is only obvious once seen, and
the cost of not seeing it is inventing a mechanism that already exists.

### And the public names a proxy serves must resolve in the mesh too

*2026-09-09, found by an internal certificate authority that could not issue.* The mesh writes every
`<node>.internal` name into every declared container and treats the public names a proxy serves as a
separate matter — *what routes it once it arrives is a proxy's, and stays separate*, above. That
holds for a client dialling by internal name. It does not hold for anything **inside** the mesh that
must reach a public name, and the first such thing to appear was the internal issuer of §5.

**An issuer validates by connecting to the name it is certifying.** Asked for a certificate for a
routed public name, the internal authority accepted the order, offered a challenge, and then could
not connect: nothing in the mesh resolved that name, so the challenge had no target. A name the mesh
can reach from the outside but cannot resolve from the inside is a name it cannot certify with an
authority of its own.

**So a granted route is published into internal resolution as well** — the routed name to the node
that serves it, mesh-wide, by the same mechanism that writes the node names. It is *given by the
mesh, not chosen by a module*, for the same reason the node names are: a module listing the routes
would go stale the day one changes. The mesh propagates the names it was told to serve and still
knows nothing about what they mean
([ADR 0066](../../02-DECISIONS/0066-public-routing-is-name-agnostic.md)).

## 3 — Exposure

Settled by [ADR 0007](../../02-DECISIONS/0007-connectivity.md); summarised here because
this is where it belongs.

**A route is a grant.** A module that must be reachable declares it needs one; the proxy provides
it and hands back the public name. Ordinary
[ADR 0009](../../02-DECISIONS/0009-modules-and-the-graph.md)
vocabulary — the mirror of a database grant, where the consumer supplies a target and receives a
name rather than supplying nothing and receiving credentials.

**A workload on an unreachable node is proxied by a reachable one, across the overlay.** Which is
the case is a mesh-level fact, which is the fourth reason exposure is controller work.

### What was built

*2026-08-31.* Nothing new in the vocabulary, which was the claim and is now the fact: a route is a
provision, a proxy provides it, and a module that must be reachable requires it. The consumer
contributes the name it wants and the port it listens on; the proxy receives every consumer that
asked; the consumer is told what the provider serves, which is how it knows its own name.

**One field was missing, and it is the one anything reaching back needs.** A contribution now
carries **where the mesh says that machine is**. A database is reached *by* its consumer, so the
mesh never had to tell a provider where anybody was; a proxy is the other direction — it is told
to send traffic to a consumer and has to open a connection. Without it every provider implementing
a provision would have to know how the mesh names machines, which is a convention leaking into
every module.

**Exposure and filtering are different questions and a module answers both.** A workload says what
it listens on and who may reach it; separately, it says it wants a route. A module that asked for a
route and not for the port is unreachable by the proxy it just asked for — which the lab
demonstrates, because the machine is already filtering by the time this runs.

**Withdrawal, which was open above.** The file the proxy is given is the whole truth about who has
a route, so a proxy replaces its table rather than merging. Merging would keep serving a name whose
module was unassigned — and *a stale public name pointing at nothing fails more visibly than a
stale grant* is the reason it must not survive, not a reason to tolerate it.

**A name a proxy does not serve is refused by saying which it does.** A route that was withdrawn
and a name that never existed are different things, and a bare 404 makes an operator go and read
the mesh to tell them apart.

*Checked in the lab by a request to the name reaching the workload across the private network and
returning the workload's own answer, then by unassigning the module and requiring the same request
to stop working.*

### The name is a label, not a domain

*2026-09-09, from running the whole mesh in the lab.* A route contribution carried its public name
in full — the forge as `git.example.tld`, spelt out in the module. Pointing the same catalogue at a
different domain — a lab standing in for production, or a second operator's mesh — meant rewriting
that name on every routed module. The mesh was holding a **map of names to services**, which is the
one thing it must not: a public name is two facts owned by two different places, and neither is the
module's manifest.

**A module contributes a label; the node contributes its public domain; the mesh composes.** The
operator chooses where the forge lives — `git`, or `code` — and that is the module's to say. The
domain is the node's, set once. The mesh joins them and grants `<label>.<public-domain>`,
interpreting neither half. Moving a mesh to another domain is one node setting, not an edit per
module.

**Today the name is still a literal, and that is the gap.** There is no interpolation of a node's
domain into a module's label, so the composition is done by a per-node override — which reproduces
exactly the per-module cost it is meant to remove. The design is the composition; the override is a
stopgap until the manifest layer can carry a label and a domain separately
([ADR 0066](../../02-DECISIONS/0066-public-routing-is-name-agnostic.md)).

### A route also carries what a request arriving at it may do

*2026-09-25, from comparing the mesh's proxy against the ingress it would replace
([issue 116](../../04-ISSUES/116-route-proxy-has-no-auth-or-ip-restriction/00-report.md)),
decided in [ADR 0108](../../02-DECISIONS/0108-a-route-carries-the-policy-applied-to-a-request.md).*

A grant hands back a name. It did not say what the name admits, and the proxy admitted everything —
its request path was a host lookup and a forward. Measured against what the replaced ingress
actually relies on, four things were missing: **authentication**, **refusal scoped to a path**,
**path-scoped routing with priority**, and **redirect**. Three modules depend on the first, each to
gate an admin surface that has no login of its own; one dependent of the second is a live incident
mitigation.

**Policy belongs to the route, not beside it.** A contribution carries it along with the name, the
port and the location. The alternative — a proxy-side settings layer keyed by route name — keeps the
grant literally clean but makes *"what protects this route"* a question answered from two files that
nothing keeps in step. A route's protection is part of what a route is.

**The set is closed at those four.** A fifth is an amendment, so each addition is earned by a
dependent that exists rather than added because a middleware surface was open. An open surface would
recreate the thing being replaced, and is far harder to narrow later than a closed one is to widen.

**Where policy needs a credential, the declaration names a secret; it never carries one.** The mesh
already mints and holds credentials, and that machinery stays the only thing that does — so a hash
never reaches anything regenerated, synced or committed.

**This re-keys the table.** Two of the four need one host routed more than one way, so the proxy
matches on host **and path**, with priority, rather than mapping a host to a single target. Equal
priorities must resolve identically every time, or the proxy stops being reproducible.

The proxy remains a reference implementation: the contract is the file the mesh writes, not the
program that reads it, and another proxy may implement the same file.

## 4 — Filtering

**Derived from what is assigned here, and from the overlay's shape** — a node's open ports are a
consequence of what runs on it and who must reach it, not an independent declaration to keep in
step by hand. That is true of a converged node; an adopted one keeps the firewall it was found
with until it converges (below).

**A rule names its source** ([ADR 0007](../../02-DECISIONS/0007-connectivity.md)).
A rule with no source is open, and must say so rather than appear to restrict something. `scope:`
is removed rather than implemented: five manifests carry it today, it is referenced by no code,
and it is the clearest instance in the repository of *an unenforced rule is indistinguishable
from a wrong one, and costs more, because people believe it.*

**Unknown keys are refused** — the discipline the host's declaration parser already has
([ADR 0005](../../02-DECISIONS/0005-the-node-host.md)), and
the one manifests lack. `scope:` survived because nothing rejected it.

### What was built

*2026-08-31. Everything above was the intention; this is what exists, and how each part is
checked. [04-ISSUES/003](../../04-ISSUES/003-firewall-scope-is-read-by-no-code/00-report.md) is
resolved by it.*

**A module says what it listens on**, as a port, a protocol and a source — `mesh`, `anywhere`, or
`machine`. The source is required and there is no default, which is the whole of *a rule names its
source*: a manifest that omitted it would read as a restriction and be none. *Checked by a manifest
with a port and no source being refused, and by one naming a source the mesh cannot render being
refused as well — the second is what stops a source becoming a comment.*

**The set is derived per node**, from every module assigned to it, not from the module asking for
it. Where two modules want the same port, the wider source wins and both are still named, because
removing one of them must not read as a reason to close a port the other needs. *Checked by
rendering a node whose firewall module has no ports of its own and asserting another module's port
is in the result; and by giving one port two modules and one source each, and asserting the
narrower rule disappears while both names survive.*

**What is not declared is closed.** The rule set drops by default. *Checked by naming the input
chain in the assertion rather than the policy alone — the first version of that test passed while
input accepted everything, because another chain in the same file also said `policy drop`.*

**From the mesh means the machines the mesh has**, as their addresses on the private network, not
as a subnet. A subnet is a guess that stays wrong quietly; the address set shrinks when a node
leaves and nobody edits anything. A machine that asks for `mesh` where the mesh knows no addresses
is **closed and told so in the file** — widening it would open a port nobody asked to open, and
dropping it silently would close one somebody did.

**Three things it deliberately does not do**, each of which looked right and would have broken
something:

| | why not |
|---|---|
| decide what the machine **forwards** | the container runtime writes its own forwarding rules and a second policy is consulted alongside them, so a drop here stops every container on the node — the controller included. Nothing in a manifest says what a machine routes, so there is nothing to derive it from either |
| **flush the ruleset** when loading | that empties every table on the machine, the runtime's among them. Only the mesh's own table is replaced, and it is declared empty first so the replacement works on a machine loading one for the first time |
| carry a **command to load itself** | the link may not carry an action ([ADR 0005](../../02-DECISIONS/0005-the-node-host.md)). A service is declared to reflect the file instead, so replacing it restarts what loads it — the shape that rule leaves, used here for the first time for its real purpose |

**A module that wants a rule set brings the unit that loads it.** Found the hard way: the unit a
distribution packages for nftables runs, applies the rules and exits, so it is neither running nor
stopped — and a host asked for a service that is "running" reports, quite correctly, that it is
stopped. Every packet was filtered exactly as declared and the machine was marked as not doing what
it was told.

**The vocabulary has no word for "ran, did its job, and exited"**, and that is a real gap rather
than a wording problem: the whole class of configuration-applying units — packet filters, sysctl,
tmpfiles — is shaped that way. Until there is one, a module ships a unit that stays, which is also
the better shape: how a machine enforces rules is a fact about the machine, and the mesh has no
business depending on what a distribution happens to package.

**One rule is derived from the overlay's shape rather than from what is assigned: a hub's own
listening port.** A hub accepts inbound connections from every node at other sites; a machine that
is not a hub dials out and needs nothing open, because a reply to a flow it started is already
accepted. The two want different rules on an *identical module*, so `listens` — a static field —
cannot say it. The machine a static answer gets wrong is the one facing the public internet, which
is the machine that most needs filtering.

*Recorded as a gap on 2026-08-31 and closed the same day.* **A computed module now contributes
listens the way it contributes resources.** The port comes from the endpoint, which is where the
interface takes its `ListenPort` from — one source, so a rule set cannot open a port the interface
is not on. It is open to *everywhere* deliberately: a node at another site is not on the private
network until this port lets it on, so restricting it to the mesh would be a rule that can never
be satisfied by the thing it exists for.

**A generator that cannot say what a machine opens is refused, not read as silence.** Closing a
port on the evidence of a failure to look is how a machine is severed by a fault somewhere else —
and the machine it would sever is the hub, whose only route to being repaired is the network it
just closed.

*Checked by filtering the hub and then requiring the mesh to keep working: a declaration still
reaches the other machine, and the other machine still reaches the hub. A rule file that looks
right and a mesh that has stopped are exactly what that guards against.*

**And it is enforced, which is what separates this from `scope:`.** Checked on two real machines:
two ports opened, one declared, and from the other machine the declared one answers and the
undeclared one does not — then the module is removed and the port closes with nobody editing a
rule. *A rule set that is written but never loaded passes every check that reads the file, which
is why the check reads packets.*

### While a predecessor still serves the same thing

*2026-09-22, [ADR 0104](../../02-DECISIONS/0104-a-provision-may-be-answered-by-an-adapter-to-the-predecessor.md).*
The mesh's proxy owns the two public ports and derives its routes from what modules contributed, so
it cannot stand beside a predecessor's proxy and cannot serve the predecessor's names. During a
migration a provision of this shape — one provider, a scarce machine-wide resource — may instead be
answered by an **adapter**: a module that provides `route` and writes each contribution into the
predecessor's own configuration, pointing at the machine port the contributing module publishes.
The predecessor's proxy goes on serving every name and renewing every certificate; the mesh's proxy
is taken last, when every route is one the mesh contributed. The adapter is refused on a converged
node, and removed when the predecessor's proxy retires. *How it is checked:* the adoption bed takes
a module behind the adapter and asserts the name answers and the predecessor's own names still do.

### On an adopted node

*2026-09-22, [ADR 0100](../../02-DECISIONS/0100-a-node-in-use-is-adopted-before-it-is-converged.md).* **The firewall found on the machine stays in force**, and the mesh
loads no table there that drops by default or holds an accept — neither genesis's base ruleset nor
the derived one. Every base chain at a hook runs and a drop in any is final, whatever the other
firewall is written in, so a second, stricter table would close every port the machine serves, and
an accept in one would open nothing the found firewall drops. What the mesh needs reachable it
declares as **openings**: a port, from where, on the incoming path or the forwarded path — a
published container port is forwarded, and a firewall that filters only incoming traffic never
sees it. The controller derives them from what the filter would be derived from, each from where
the filter would admit it: the assigned modules' `listens`, the hub's port, the bus and the registry
from anywhere; the store's port and the broker's management port from the private network. The host converges each opening through
the found firewall in that firewall's own terms, marks it as the mesh's, removes only what it
marked, and re-checks every opening on each reconcile so a reload or a reboot does not lose it for
longer than one reconcile. An opening is state, not a command, so it travels over the link like any
other resource. **The mesh guards its own ports in a table of its own that only refuses** —
passing everything by default and holding nothing but refusals, and the found firewall's reload
does not touch it. Its ports are derived ([ADR 0103](../../02-DECISIONS/0103-what-an-adopted-node-holds-and-what-its-guard-refuses.md)): every machine port a
*taken* module publishes that the filter admits from the private network only, with the store's
port and the broker's management port. A port of a module not yet taken may still be the
predecessor's, so it is not guarded; and only packets addressed to this machine are matched, so
traffic it routes for others passes. An opening a found rule already answers is not added, so
removing it never removes the operator's rule. It refuses those ports except from
the private network and the machine itself — loopback and the container runtime's networks, known by the interface a packet arrives on, never by
its source address alone — at
the prerouting hook, before the container runtime redirects the packet, so it matches the port the
packet was sent to, for both address families; the
bus, the registry and the hub's port stay reachable from anywhere, as a node enrols and pulls
before it has a private-network address. One kind of found firewall is spoken; a machine with none
needs no openings, and a machine with another kind is refused adoption. Converging the node refuses
while a found container is still held; otherwise it previews what is reachable now — listening
sockets and published ports — what will close and which modules it will take, then loads the
derived filter in place of the refusal-only table and disables the found firewall without flushing
it. *How it is checked:* the adoption bed asserts the found firewall's rules differ only by the
mesh's marked rules, that the store is unreachable from off the private network before and after
the found firewall reloads and reachable from a container on the node, that a machine not yet enrolled reaches the bus, that a second machine
enrols through the openings before and after a reload and a reboot, and that after the flip the
declared port is open and the undeclared one closed.

## 5 — Certificates

**Two authorities, kept separate on purpose.**

| | issued by | for |
|---|---|---|
| **public names** | a public ACME authority | anything outside the mesh reaches |
| **internal names** | the **mesh CA** | node-to-node, over the overlay |

**The split is not collapsed, including in the lab.** A single-CA lab would hide any bug living
in the split, so the lab runs its own ACME issuer on its public segment and keeps the mesh CA
unchanged ([research 004](../../01-RESEARCH/004-lab-network/00-overview.md)).

**Public issuance requires genuine public reachability.** The HTTP-01 challenge must be answered
at the name being certified, so issuance happens through a publicly reachable node regardless of
where the workload runs — the same asymmetry as exposure, for the same reason.

**The issuer must be configurable.** Today it is not: the proxy sets no `caServer` and therefore
defaults to the public authority's *production* endpoint. Two consequences, and the second is
worse than the lab problem that found it — every certificate experiment on a real node consumes
production issuance quota, and a retry loop can exhaust it for a week.

**The mesh CA is not a bootstrap concern.** A joining node verifies the controller against the
fingerprint in its token ([ADR 0004](../../02-DECISIONS/0004-a-node-and-how-it-joins.md)),
so nothing needs the CA before membership. It certifies internal names afterwards, and that is
all it does.

**The internal authority makes its own root at first start, and a consumer fetches it**
([ADR 0098](../../02-DECISIONS/0098-a-fact-a-provider-makes-at-first-start-is-fetched-from-it.md)).
The mesh mints the authority's password and nothing else of its: a root certificate and its key
are things only the authority can make, and a served fact written in a manifest cannot carry what
does not exist until the authority has run. So the authority serves its root at a path beside its
ACME directory, and the proxy that requires it fetches that root over the mesh network in a
run-once step before it starts. The step names the binding it reads and the proxy names the
step, so when the authority moves the root is fetched again and the proxy is recreated with it
([ADR 0099](../../02-DECISIONS/0099-a-step-that-runs-once-names-what-it-reads.md)).
*How it is checked:* the route-forwarding bed installs the authority, the proxy and a consumer
from the catalogue and asserts the routed name is served.

### What was built

*2026-08-31.*

**A node generates a fourth key**, and the reason is the one the other three already give: *a key
used for two purposes is one rotation away from breaking the other.* The identity key would work
for TLS and reusing it would mean rotating a node's identity every time its certificate is
replaced. The private half never leaves the machine; the mesh is told the public half at
enrolment.

**So there is no certificate request and nothing to seal.** The mesh signs a statement binding a
public key to a name it alone assigns, which is the whole of what a certificate authority does.
It issues rather than stores: the node's key does not change, so signing again produces an equally
valid certificate and there is nothing to keep in step.

**A machine with no name inside the mesh is refused**, not given a certificate for nothing. A
certificate for a name nothing resolves is a certificate nothing can check.

**And the key is stored in the format a server reads** — PKCS#8 PEM, not the host's own encoding.
That is not an implementation detail of whoever writes the file: the file exists *because
something else reads it*, so the format is the interface
([04-ISSUES/014](../../04-ISSUES/014-a-key-that-is-present-and-unusable/00-report.md)).

*Checked by a real handshake between two machines: one serves on its internal name with the key it
generated, the other verifies against the mesh's authority and nothing else. Every cheaper check
passed while the server could not start — the key was present, the certificate was valid, and
nothing read either the way a server would.*

### An internal issuer, pointed at and trusted

*2026-09-09, from wiring one to the proxy in the lab.* §5 above asks for two things this build
leaned on: the issuer must be configurable, and the lab runs its own ACME authority rather than
collapsing the split. Wiring the proxy to that authority is the whole of it — the proxy is told
**which** issuer to use and given that issuer's **root** to trust, and every other step of issuance
is unchanged. **The same code path certifies against an internal authority as against a public one;
only the issuer differs.** That is what makes trusted certificates possible for a mesh whose names
the public internet cannot resolve.

**And it does not work until the routed name resolves inside the mesh** — the §2 finding above,
arriving here because this is what needed it. The authority's challenge reaches the routed name only
once that name is in internal resolution; a public authority is handed that dependency by public
DNS, and an internal one has to be handed it by the mesh. *Checked by a handshake to a routed name
that verifies against the internal root and nothing else — which cannot succeed unless the issuer
first reached the name to certify it*
([ADR 0066](../../02-DECISIONS/0066-public-routing-is-name-agnostic.md)).

## What this removes

The list is worth having in one place, because it is most of the argument:

- **The last two direct database connections from nodes** — `wireguard` and `traefik`, the only
  two, both connectivity.
- **Therefore the database credential on every node**, and the object-store credential beside it.
  [ADR 0004](../../02-DECISIONS/0004-a-node-and-how-it-joins.md)'s central claim becomes
  true rather than aspirational.
- **The `/etc/hosts` floor**, and the bootstrap circularity it patched.
- **Hub election by address prefix**, and the silent no-hub failure when nobody knew the
  convention.
- **The RFC1918 inference**, and the lab substitution that existed to satisfy it.
- **`scope:`**, and the class of manifest key that means nothing.

## Open

- ~~**What happens when the hub is down.**~~ **Resolved** by
  [ADR 0006](../../02-DECISIONS/0006-the-substrate-and-the-control-plane.md), together with `06`'s
  matching question — they were one question. Nothing takes over. WireGuard has no failover, the
  hub is declared rather than elected, and non-co-located paths stop while co-located direct peers
  and every already-assigned workload keep running. The recovery path is restore, and its deadline
  is certificate renewal.
- **Renumbering the overlay.** Made *possible* by declaring the hub rather than inferring it from
  an address, but no procedure exists, and a graph delivered node by node has an ordering problem
  while it is half-applied.
- ~~**Revoking a route** when a module is unassigned.~~ **Resolved** 2026-08-31 — see §3. The file
  a proxy is given is the whole truth about who has a route, so a route does not outlive the module
  that asked for it.
- **IPv6.** [ADR 0007](../../02-DECISIONS/0007-connectivity.md) makes
  it expressible; nothing here says the overlay or the resolver handle it.
- **Reporting declared-versus-observed.** ADR 0007 makes the disagreement detectable and does not
  say who looks or what they are told.
- **Composing a route name from a label and a node's domain.**
  [ADR 0066](../../02-DECISIONS/0066-public-routing-is-name-agnostic.md) makes the public name the
  operator's to move between meshes, but the manifest layer still stores it as a literal — so today
  the composition is a per-node override rather than the design. The interpolation that would let a
  module carry a label and a node carry the domain, and the mesh join them, does not yet exist.
- **Publishing route names into internal resolution.** The same ADR requires a granted route to be
  resolvable inside the mesh, not only routable from outside it; the mechanism that writes
  `<node>.internal` into containers does not yet also write the routed names, which is why an
  internal issuer cannot currently validate one without a hand-placed entry.

## The hub adopts the predecessor's tunnel

*2026-09-23, [ADR 0105](../../02-DECISIONS/0105-the-mesh-adopts-the-predecessors-tunnel-in-place.md).*

On an adopted node that is the hub, the private network is not raised beside the tunnel it finds;
it **takes it over**: the found interface's private key, its port, its address and range, and every
peer it had, carried as peers not yet enrolled. The found interface is stopped, its configuration
kept on disk. A predecessor machine sees the same server key at the same endpoint and cannot tell
the tunnel changed hands; when it enrols, it keeps the address the tunnel already held for its key.

The mesh's own addresses are the adopted range's — every binding, hosts entry and endpoint the
controller composes follows it, as readers of a setting. ADR 0100's non-overlap rule applies only
where a found tunnel is left running beside the mesh's; where it is adopted there is one tunnel.
The guard admits the mesh's ports from that one interface, and the predecessor's peers arrive on
it.

*2026-09-27, [ADR 0127](../../02-DECISIONS/0119-a-taken-tunnels-predecessor-is-retired.md).* The
found configuration is kept only until the take is proven — the found unit down, the mesh's
interface up and handshaking with a peer. Then it is removed from where the found unit reads it
(its original stays kept), the hold ends, and the predecessor's tunnel cannot be raised again by
anything but a person restoring it by hand. Undeclaring the private network does not bring it back.

## The bus is NATS

*2026-09-23, [ADR 0106](../../02-DECISIONS/0106-the-bus-is-nats.md). Architecture to be written
before code; this section names the shape only.*

Every link the mesh has rides NATS subjects; durability is JetStream's; a module's account is a
NATS account with permissions derived from `emits`/`consumes`, declared as configuration the host
writes and the server reloads. The sdk's contract is unchanged. The adopted AMQP broker stays as
the predecessor's compatibility broker until its last client is gone. Built in the lab beside the
migration; cut over in one rollout after the core; the person's client is designed on it.