jschoubben
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ADR 0119 rejected giving the old broker a retirement condition and said why: "its clients are not only the predecessor's, so the retirement condition describes a day that will not come". The operator has said that day is coming — the predecessor is deprecated, some of it still running, none of it being migrated, left to stop rather than moved. Recorded because three documents reason from the premise it overturns. Design 25 §5's "no day anything is waiting for", §9's "the predecessor's clients never notice", and design 28's closing note that the predecessor's world does not need to move. **And it needs no new machinery, which is 0119 being paid off rather than revised.** Because that record made the broker an ordinary provider rather than a compatibility module, ending it is unassigning a provider whose provision nothing requires — something the module system has done since it existed. So step 5.3 finishes instead of trailing off, and the transitional double announcement of a build outcome has a date. The consequence worth planning around: the predecessor's own mesh talks over that broker, so shutting it down ends the tooling that reaches this installation's machines from a workstation. The rollout is driven from the node, or driven before the broker stops. That is a sequencing constraint on 5.2, not an afterthought. What survives is `amqp` as a provision: a module that genuinely needs an AMQP broker can still be given one. What retires is this broker's role as the predecessor's.
3.6 KiB
topic, status, date, deciders, reconstructed, extends
| topic | status | date | deciders | reconstructed | extends |
|---|---|---|---|---|---|
| the mesh | accepted | 2026-09-27 | jochen | false | 02-DECISIONS/0119-amqp-is-a-provision-not-the-bus.md |
122. The predecessor is ending, and its broker goes with it
Context
ADR 0119 settled that the old broker is an ordinary
provider of the amqp provision rather than a compatibility module with an end date. It rejected
giving it a retirement condition, and said why: "its clients are not only the predecessor's, so the
retirement condition describes a day that will not come."
The operator has said that day is coming. The predecessor is deprecated. Some of it is still running, and it is not being migrated — it is being left to stop. Its broker may be shut down.
That is a fact about this installation, not a change of mind about what a broker is. It is recorded because three documents reason from the premise it overturns: design 25 §5 and §9, and design 28's closing note that the predecessor's world "does not need to move: its broker is the compatibility module until its last client is gone."
Decision
The predecessor's broker retires when nothing requires amqp, by being unassigned like any other
provider. No retirement condition, no end-date machinery, no special case — which is ADR 0119 being
paid off rather than revised. Because that record made the broker an ordinary provider, ending it
needs nothing that does not already exist: a provision with no consumers has its provider unassigned,
and the module system has done that since it existed.
So step 5.3 has an ending. "The mesh's own accounts removed from the deprecated broker" was written as the last thing that could be said, because the broker itself was going to outlive the question. It now finishes: once the mesh's own traffic has moved and the predecessor's remnants have stopped, the module is unassigned and the port is free.
And the transitional doubling has a date. The build outcome is announced under both the module's name and the role's on the old bus, so that a catalogue deployed before the rename and one deployed after both hear it. That exists only while the old bus does, and goes with it.
Consequences
The remote access path goes with it, and that is the one practical consequence worth planning around. The predecessor's own mesh communicates over that broker — so shutting it down ends the tooling that reaches this installation's machines remotely. Work on the node after that point is done from the node. This matters most for the rollout, which is the step that would otherwise be driven from a workstation: it has to be driven locally, or driven before the broker stops.
What is still running on it stops when it stops. Some of the predecessor's services are live and are not being moved. That is the operator's decision and it is recorded here so that nobody later reads a broker with clients as an accident.
Nothing in a served request's path is affected. Modules serve from their own containers; the mesh's bus carries the mesh's own traffic — declarations, reports, events, tool calls. This was checked rather than assumed when the question came up, and it is why the operator's position ("as long as my services keep running") is a bounded risk rather than a gamble.
One reason to keep the broker survives: amqp remains a provision a module may require, and a
module that genuinely needs an AMQP broker can be given one. What retires is this broker's role as
the predecessor's, not the mesh's ability to provide the thing.