---
layer: as-is
status: implemented
code: [hal]
updated: 2026-08-23
decisions:
  - 02-DECISIONS/0011-managed-files-are-generated-never-edited.md
  - 02-DECISIONS/0009-modules-and-the-graph.md
---

# Configuration and secrets

Every value a module reads at runtime comes from a file on a node's disk. Every one of those
files is **generated**.

## The rule

A managed file is derived from the mesh database. A synchroniser rewrites it when the values
behind it change. The write path is the mesh operation that owns the value; the file is an
output ([ADR 0011](../../02-DECISIONS/0011-managed-files-are-generated-never-edited.md)).

An edit to a managed file survives until the next synchronisation and is then overwritten
silently, taking whatever it was fixing with it — bringing back the bug the edit had removed,
with a delay, and with no error to connect the two events.

There is a way to ask whether a given file is managed. That question has to be asked, because
the answer is not visible from the file.

## What is managed

Generated environment files for each module, service definitions in each module's runtime
directory, managed configuration files a module declares, and node-level settings. The list is
not a category — it is whatever a synchroniser claims, which is why the question is asked of
the tooling rather than answered from a rule.

## How a value is decided

Values resolve by precedence, highest first:

1. **A database override** — set deliberately, or written by a provisioner.
2. **The value already in the generated file** — preserved for anything without an override.
3. **A generated value** — a random secret, a template composed from other variables, or a
   value pulled from the node's own record.
4. **The manifest default.**

Two consequences follow, and both are subtle enough to have caused confusion.

The second rule is what keeps a generated password **stable** across regenerations. It is not
an oversight; without it every regeneration would issue a new secret and break whatever holds
the old one.

The same rule means that **changing a manifest's default does not change anything already
using it**. The existing file's value wins. The new default reaches only installations that
never had one.

Removing a declaration is worse than changing it: the old override row and the file it produced
are both left behind. Configuration is additive in practice, whatever the manifest says.

## Secrets

Generated secrets are produced by the mesh, never authored. Provisioned credentials arrive as
database overrides written by the provisioner and are marked as such, so they can be
distinguished from a deliberate override and cleaned up when the grant is removed
([ADR 0009](../../02-DECISIONS/0009-modules-and-the-graph.md)).

Nothing in the repository contains a credential. The repository has no per-node content at all,
which is what makes that guarantee structural rather than a matter of care.

Two known weaknesses, both recorded rather than resolved:

**Generated environment files were world-readable.** The mode passed at write time only applies
when the file is created, so regeneration left the previous mode in place. The class of bug is
worth remembering beyond the instance: a permission set at creation is not a permission
maintained.

**Rotation is not a mesh operation.** Secrets can be generated and granted; there is no
mechanism that rotates one and informs everything holding it. Where a rotation has been done,
it has been done by hand, and doing it wrong has taken services down.

## Node-level and mesh-level values

A node-level value applies to everything on one node. A mesh-level value applies everywhere and
is read by every node — the broker's location is the canonical example, and a wrong one is how
a mesh fails to form.

Neither is a file that anyone edits. Both are database records that produce files.