Design Notes
This section explains the architecture and implementation choices in Barn 0.9.0.
Start with the product model, then follow the boundaries outward:
- Why Barn has no projects — one inventory, one owner-scoped deployment, and no second source of truth.
- Why every node has two NICs — fixed identity for the lab, separate from management egress.
- Declarative does not mean destructive — per-node drift with explicit recreate and removal.
- A PID is not a virtual machine — QMP identity, process evidence, journals, and bounded recovery.
repo.yamlis intent;catalog.jsonis evidence — a static image repository whose generated metadata is checked against the actual qcow2 bytes.
Use the documentation for commands and configuration, and Platforms and Limits to check whether Barn fits your host.
repo.yaml Is Intent; catalog.json Is Evidence
Why Barn separates human-authored image policy from generated metadata that must match the actual qcow2 artifacts.
A PID Is Not a Virtual Machine
Why Barn combines QMP identity, process evidence, typed invocations, and journals before it signals or deletes anything.
Declarative Does Not Mean Destructive
How Barn uses per-node hashes and explicit operations so missing configuration can never authorize deletion.
Why Every Barn Node Has Two NICs
Why Barn separates management egress from the fixed-address network used by the host, peers, Ansible, and Pigsty.
Why Barn Has No Projects
Why Barn replaced per-directory project state with one owner-scoped deployment driven by one Pigsty inventory.
-
repo.yaml Is Intent; catalog.json Is Evidence
This article describes Barn 0.9.0. The VM lifecycle and network design here apply to Linux guests; Mac machines are managed independently. A static image repository sounds like a directory of qcow2 files plus a JSON index. The difficult part is …
This article describes Barn 0.9.0. The VM lifecycle and network design here apply to Linux guests; Mac machines are managed independently. A static image repository sounds like a directory of qcow2 files plus a JSON index. The difficult part is …
-
A PID Is Not a Virtual Machine
This article describes Barn 0.9.0. The VM lifecycle and network design here apply to Linux guests; Mac machines are managed independently. A pidfile answers one question: which integer did a process have when the file was written? It does not prove …
This article describes Barn 0.9.0. The VM lifecycle and network design here apply to Linux guests; Mac machines are managed independently. A pidfile answers one question: which integer did a process have when the file was written? It does not prove …
-
Declarative Does Not Mean Destructive
This article describes Barn 0.9.0. The VM lifecycle and network design here apply to Linux guests; Mac machines are managed independently. “Declarative” is often shortened to “make reality equal the file.” That is a useful slogan until the file is …
This article describes Barn 0.9.0. The VM lifecycle and network design here apply to Linux guests; Mac machines are managed independently. “Declarative” is often shortened to “make reality equal the file.” That is a useful slogan until the file is …
-
Why Every Barn Node Has Two NICs
This article describes Barn 0.9.0. The VM lifecycle and network design here apply to Linux guests; Mac machines are managed independently. A Pigsty inventory names machines by stable addresses. PostgreSQL replication, etcd membership, HAProxy …
This article describes Barn 0.9.0. The VM lifecycle and network design here apply to Linux guests; Mac machines are managed independently. A Pigsty inventory names machines by stable addresses. PostgreSQL replication, etcd membership, HAProxy …
-
Why Barn Has No Projects
This article describes Barn 0.9.0. The VM lifecycle and network design here apply to Linux guests; Mac machines are managed independently. Barn began with a familiar VM-manager abstraction: a working directory was a project, a hidden marker gave it …
This article describes Barn 0.9.0. The VM lifecycle and network design here apply to Linux guests; Mac machines are managed independently. Barn began with a familiar VM-manager abstraction: a working directory was a project, a hidden marker gave it …