Closes the two open questions in 06 and 08, which turned out to be one
question: how many control planes run, and what happens when the hub is down.
Both were drifting toward redundancy by default -- a standby plane, a second
hub, an election to pick between them. That is not one feature but a property
every layer must then honour, and each layer gets it wrong independently.
Not wanted, and not needed. A handful of machines with one node hosting the
registry is not a distributed system.
The argument for why this is sound rather than merely cheap is that the design
already tolerates it by construction. ADR 0036 makes reachability state rather
than class; the host reconciles from its own store (0043) and never needed to
ask anybody to hold the state it was last given. So the control plane being
down is not a new failure mode -- it is every node in the ordinary disconnected
situation at once. What is lost is change, not operation.
No node holds a contended role: the control plane is assigned like any other
module, and the overlay hub is declared (0050). No promotion, no quorum, no
fencing, no split brain, no replicated store, and no "which node is
authoritative" recurring at every layer.
Two consequences stated plainly rather than buried. The control-plane node is a
single point of failure -- deliberate, and said out loud so it stays
deliberate. And recovery is restore rather than failover, which makes backup
the availability story rather than hygiene.
The sharpest one is the clock: the control plane owns certificate issuance
(0049), so an outage outlasting a renewal window expires every public name.
That bounds how long recovery may take, and nothing measures it today.
Written as one document 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.
The through-line is that none of the five can be answered by a machine alone,
so all five are decided centrally and delivered as `file` resources. That costs
no new host vocabulary and removes both remaining direct database connections
from nodes -- wireguard and traefik are the only two, and both are connectivity.
Three decisions fall out, all proposed:
0050 -- reachability is declared, not inferred from an address. The RFC1918
regex is wrong for carrier-grade NAT (100.64/10 tests as public, so an endpoint
is written to an address nothing can reach), wrong for IPv6, and wrong for a
routable address behind a closed firewall. The lab needing TEST-NET-3 to
satisfy the regex is the same bug from the other side. Also kills hub election
by address prefix, which fails silently and makes renumbering an outage.
0051 -- the enrolment token carries where the mesh is and how to recognise it.
Closes two circles with one mechanism: verifying the mesh needed the CA, and
obtaining the CA meant trusting whoever handed it over; and a node had to reach
the mesh before it could resolve any mesh name. An address plus a fingerprint,
carried out of band, resolves both -- and closes the CA question 0049 deferred.
0052 -- a filter rule names its source. `scope:` is declared in five manifests,
is part of no rule type, and is referenced by no code, so those manifests
appear to restrict ports and restrict nothing. Removed rather than implemented;
the general fix is refusing unknown keys, which the host already does and
manifests do not.
Also corrects two claims in 0049 asserting wireguard was already handled.
Research 006 says both modules still reach upward; neither is.
jschoubben