Issue 067 — a provision cannot name which provider serves it

The mesh models provisions as mesh-scoped (one provider of a kind, a single mesh-store). But node-specific services delivered to the mesh was the plan from the start: both nodes already run their own postgres, SQL server, redis and object store, and identity — currently single — already serves apps on a second node. The model cannot express which provider serves a consumer, so it collapses a deliberately per-node fleet to one. Provider scoping is a whole-mesh decision across postgres/s3-bucket/oidc, not an SSO patch. Claude-Session: https://claude.ai/code/session_01D6qtiYU3P9jk3pnAXyAFyx
2026-09-20 21:24:42 +02:00
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 status: open
 opened: 2026-09-20
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 # A provision cannot name which provider serves it
 ## Symptom, as observed
 The mesh models every provision — `postgres-database`, `s3-bucket`, `amqp`, a
 future `oidc` — as **mesh-scoped**: there is one provider of a given kind for the
 whole mesh, and a consumer that requires the provision is bound to *that* one.
 `scope: "mesh"` is written into the provision definitions, and the adopted store
 is a single `mesh-store`.
 The mesh being migrated onto is not shaped that way, and never was meant to be.
 **Node-specific services delivered to the mesh was the plan from the start.** Each
 node already runs its own provider of the same kinds:
 - Both control-capable nodes run their **own general-purpose postgres server**
  (the same image, one per node), serving that node's own applications.
 - Each node runs its **own** SQL server, its **own** redis, its **own** object
  store — infrastructure is per node, by design, not a single mesh-wide instance.
 - Identity is the *only* provision that is currently single (one realm on one
  node), and even that already serves applications hosted on a **second** node.
 So the multi-provider reality is not a future edge case that appears "the day a
 second provider is added" — it is the founding topology, true today, on every
 provision kind. What is missing is any way to **say it**. A consumer requires
 `postgres-database`; it cannot require *this node's* postgres rather than *that
 node's*. It requires `oidc`; it cannot name which node's identity provider. The
 mesh model collapses a deliberately per-node fleet down to one mesh-scoped
 provider, and a consumer has no field in which to choose.
 ## Why it matters beyond this instance
 - **The model regressed an intended topology, it did not merely miss a corner
  case.** "Node-specific services delivered to the mesh" is the design; `scope:
  "mesh"` with a single `mesh-store` expresses the opposite. This is a gap between
  a stated intent and what the manifests can represent, which is exactly what the
  issues process is for.
 - **It is not an identity special case.** The missing concept — *a provision has a
  provider, providers are per-node, and a consumer names the provider* — is the
  same for databases, object stores, brokers and identity. A fix aimed only at SSO
  would leave the same wall standing behind postgres and minio, both of which are
  *already* multi-provider on the live mesh.
 - **The single-provider assumption is silent.** Nothing rejects a second provider
  of a mesh-scoped provision; the model just cannot address it, so a consumer binds
  to whichever one is "the" provider — by accident of there being one, or by a race
  when there are two. A rule enforced by nothing ("there is one provider per
  provision") reads as true until the second node's provider makes it false, with
  no diagnostic at the seam.
 - **It blocks the migration concretely.** The mesh already has applications on one
  node depending on another node's provider (identity today; databases the moment
  an app is assigned to a node whose local postgres is not "the" mesh store).
  Modelled as mesh-scoped, that topology is expressible only by accident. To carry
  it deliberately the provision must be able to name its provider.
 ## Open questions
 - Where does the provider name live — on the provision definition (`scope: "node"`
  with a provider identity), on the requirement in the consumer's manifest, or
  supplied only at assignment time so the same module can be bound to different
  providers on different assignments?
 - Is "mesh-scoped" still a legitimate scope for some provisions (a single mesh CA,
  say), or does every provision become node-scoped, with a single instance
  expressed as "there happens to be one"?
 - What is the default when a consumer names no provider — bind to the node the
  consumer is assigned to (co-located provider), require the name always, or fall
  back to a mesh-wide default provider where one is declared?
 - How does a provider's identity survive being moved between nodes, so a consumer's
  recorded choice does not silently rebind when the provider relocates?
 - Does this interact with secret rotation (the issue-scope of `rotate`) — must
  rotation address a specific provider's credential holders rather than "the
  provision's"?