---
topic: building it
status: accepted
date: 2026-09-21
deciders: jochen
reconstructed: false
extends: 02-DECISIONS/0085-a-secret-is-a-provision.md
---

# 86. A secret reaches a process as a file, and an exception is declared

## Context

The mesh seals a secret to the machine that uses it and discards the plaintext; the host unseals it
into a file at 0600 ([ADR 0048](0048-a-provider-creates-the-credential-the-mesh-minted.md)). Then
the module hands it to its container through an env-file, and the runtime puts it where anything
on the machine that can talk to the runtime can read it: `docker inspect` prints it, and
`/proc/<pid>/environ` holds it for the life of the process
([issue 041](../04-ISSUES/041-a-sealed-credential-ends-up-in-the-process-environment/00-report.md)).

Two facts made this a decision rather than a fix. **It is a supported shape**: placing
`${secret:…}` in a file a container reads as its environment is what playbook 06 shows, and 36
containers in 25 catalogue modules do it, the controller's own among them. And **nothing says which
secrets are exposed**: a reader cannot tell from a manifest whether a credential is protected from
`inspect` or not, because the manifest looks the same either way. The vault
([ADR 0085](0085-a-secret-is-a-provision.md)) rests on the seal this undoes.

## Considered Options

1. **Leave it: the environment is where configuration goes.** Rejected — it gives the sealed value
   back to a routine operation, and the care taken to seal it is then theatre.
2. **Refuse every secret in an environment.** Rejected — some software reads its configuration
   from the environment and nothing else, and a rule the catalogue cannot obey is a rule that gets
   switched off.
3. **A secret reaches a process as a file; an environment exception is declared, with a reason,
   and refused otherwise.** Adopted.

## Decision

**A secret reaches a process as a file.** A module mounts the file the host wrote and points the
program at it; the mesh's own programs accept a `_FILE` twin for every variable that carries a
credential, the way the controller's store connections already did.

**A container that reads a secret from its environment says so.** The manifest key
`secrets-in-environment` on the container carries the reason. It is catalogue-level — the host
never sees it — and it exists so a reader can tell from the manifest which secrets are exposed
that way and why.

**Everything else is refused.** A `${secret:…}` placeholder inside a container's `env` is never
filled and is refused outright. A file carrying a secret that a container names in `env-file` is
refused unless the container declares the exception.

## Consequences

The property *a sealed credential is readable only where it is used* becomes a manifest-level
fact: true where no exception is declared, stated where one is. The controller reads all six of
its credentials from files; the 35 other containers are marked with their reason and convert one
by one where their software accepts a path, which is per-module work under
[issue 041](../04-ISSUES/041-a-sealed-credential-ends-up-in-the-process-environment/00-report.md).

What got harder: a module author meets one more refusal, and the reason they write is only as
honest as they are. What is not decided: the reach of the exposure on a node — which identities can
talk to the runtime — which decides whether a declared exception is a hardening item or something
sharper.

## How it is checked

The catalogue engine refuses at composition, before anything reaches a machine, and its tests
refuse both shapes and prove the reason is stripped from what is sent.

## References

- [issue 041](../04-ISSUES/041-a-sealed-credential-ends-up-in-the-process-environment/00-report.md)
- [ADR 0048](0048-a-provider-creates-the-credential-the-mesh-minted.md), [ADR 0085](0085-a-secret-is-a-provision.md)
- [`03-DESIGN/01-to-be/13-credentials-and-their-rotation.md`](../03-DESIGN/01-to-be/13-credentials-and-their-rotation.md)