The other half of ADR 0038, and what 04-ISSUES/028 was actually about.
A module can now avoid colliding with another module; until this it
could not avoid colliding with the mesh itself.
The substrate is not a module. A node raises it from the bundle it
carries before any mesh exists, so the control plane had never heard of
the store, the broker, or its own container — and handed a database
module 5432, which the store already had.
So the machine says. The host records what each resource binds,
distinguishing what it carried from what the mesh sent — a distinction
that already existed so the two never remove each other — and reports
the carried ones. The node states and this context writes, which is the
shape of every message between them.
What the declaration binds, not what is open. A machine's open ports are
a moving target, and assigning around them would mean a port that was
free when it was asked for and taken when it was used.
Replaced whole each time rather than merged: a machine that gave a port
back must be believed about that too, and a set that only grows keeps a
port reserved for something no longer there.
Tested against a real database, and the tests bite — removing the check
hands the module 20000, which the machine had said it holds.
novox/hq ADR 0038. A module cannot choose a port: it is written once and
assigned anywhere, so any number it picks is a guess about a machine it
has never seen. A database module met the mesh's own store on 5432 and
was told, by a container runtime three layers down, that the port was
already allocated.
The number used to appear three times in every module — the rule set,
what a consumer is told, and what the runtime publishes — agreeing only
because one person wrote all three. Now it appears once, in `listens`,
and the other two are derived: the container publishes `20000:5432`, the
consumer is told 20000, and the rule set opens 20000.
An assignment is made once and kept, as a credential is. A port that
moved on every declaration would restart both ends each time and hand a
consumer a number that was true when it was read.
Ports the protocol fixes — mail on 25, submission on 587, DNS on 53 —
say so, and are then claims: one holder per machine, and the second is
refused by name at assignment. That is the mechanism the mesh already
has for what is singular on a machine, pointed at ports.
A mapping written the long way is left exactly as it is. Some things
must be pinned by hand, and quietly overruling somebody who wrote both
halves would be worse than not offering the short form.
Still open, and known: the substrate is not a module, so the mesh has
never heard of its own store and cannot yet assign around it. That is
what 028 will still be about after this.
jschoubben