Deployment¶

The agent clones or fetches the repository, resolves its own manifest, and reconciles.

Git
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Datum agent

There is no server, no database and nothing that has to reach the host in order for it to reconcile. A machine behind NAT with outbound access to a Git remote is fully manageable, and no central outage can stop a host from reconciling.

The agent opens one optional listener, the metrics endpoint, bound to loopback by default and disableable. Nothing arriving there changes what the host applies, so a host that never exposes it reconciles exactly the same way.

What this costs¶

Every managed host needs read access to the whole repository. Resolution requires every Layer and every Host document, so a host cannot be given only its own configuration, and anything committed to the repository is readable by every machine under management. A single compromised host exposes the fleet's configuration, not just its own. Secrets are referenced and resolved on the host for that reason.

Host identity is not a security control. A machine that claims to be a different host gains nothing it could not already read, which is why identity is about classification, not access.

Fleet-wide status is awkward. Each host holds its own result and nothing aggregates them, so answering which hosts are converged means collecting from each one.

The manifest is the seam¶

Everything after composition consumes the effective manifest and nothing else from the repository. The graph builder, observer, planner and reconciler never read a Layer, evaluate a matcher, or examine the revision beyond recording it.

graph TD
  subgraph resolution["Resolution"]
    repo[Repository] --> resolver[Fleet resolver]
  end
  resolver --> manifest[Effective manifest]
  subgraph engine["Reconciliation engine"]
    manifest --> builder[Graph builder]
    builder --> observer[Observer]
    observer --> planner[Planner]
    planner --> reconciler[Reconciler]
  end

Keeping resolution and reconciliation on opposite sides of a serialisable artefact is ADR-0007. It costs the manifest a canonical form it would not otherwise need, and it buys an engine that can be tested against a manifest with no repository and no host in the picture.