Paul Payne
add356dcf2
A derived, mostly-computed model of how programs, deployments, and repos relate,
plus the git-sync surfaces that motivated it. See docs/relationships.md.
Core:
- `requires: [{kind, ref, version?, bind?}]` on programs + deployments — one
precondition relation; `system_dependencies` is its `{kind: system}` alias.
kind fixes meaning + check (system=installed, deployment=exists).
- relations.py: derives repos (git toplevel / monorepo), fan-in, and the
predicates functional?/fresh?/deployed? — nothing stored.
- env is generated FROM a `{kind: deployment, bind}` requirement (target URL →
consumer env), never scraped back into one; explicit defaults.env still wins.
- git.py: working-copy status/pull, repo toplevel + remote url.
Surfaces:
- `castle graph` + GET /graph — the relationship diagnostic.
- GET /repos, /repos/{key}/git|sync — repo-scoped sync (a repo is the sync unit;
a monorepo backs several programs). GET /programs/{name}/git|sync + repo context.
- Dashboard: Graph screen, program-page git status + repo-aware Sync, and a
monorepo banner on Programs.
Governing principle: predicates are derived; encode only the non-derivable, as a
node or edge property. Pull-only sync — converge stays a separate step.
91 lines
4.4 KiB
Markdown
91 lines
4.4 KiB
Markdown
# Relationships: requires, repos, and derived predicates
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How castle models the relationships between **programs**, **deployments**, and
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**repos** — and answers questions like *"is this functional?"*, *"is it fresh?"*,
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*"is it deployed?"* — with the smallest possible amount of stored state.
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## The governing principle
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> **Predicates are always derived. Encode only what is not derivable.**
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A *predicate* is a question we ask about a program or deployment: `functional?`,
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`fresh?`, `deployed?`. None of these are ever stored — each is a **function** over
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data castle already has (git, config, the registry). When a predicate can't be
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answered from derived data, find the one missing datum and ask: is it about the
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**thing** (a node property) or about a **relationship** (an edge property)? Encode
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*only* that datum. Everything else stays computed.
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This is the same instinct as `kind` (derived from `manager`) — we don't store what
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we can compute, and a relationship that proves real and stable in the derived graph
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is a candidate to *promote* into a first-class concept. Diagnostic → evidence →
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abstraction, in that order.
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## Entities
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- **program** — the software catalog entry.
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- **deployment** — a program realized on this node (`kind` derived from `manager`).
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- **repo** — a git working copy. **Derived** from `git rev-parse --show-toplevel`
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on each program's source; several programs sharing one toplevel is a *monorepo*.
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Never stored.
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## The one encoded relation: `requires`
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Everything we were calling "substrate", "wiring", or "dependency" is one relation —
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**`requires`** ("A must have B to be functional") — with a typed target. The
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**kind fixes the meaning and the check**; there is no separate purpose/`for` tag:
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| kind | means | checked by |
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|------|-------|-----------|
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| `system` | the host package/binary must be **installed** | `which <ref>` |
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| `deployment` | another deployment must **exist / be running** | registry / config |
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```yaml
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requires:
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- { kind: system, ref: pandoc } # today's system_dependencies
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- { kind: deployment, ref: astro-guru, bind: GURU_URL }
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# - { kind: deployment, ref: litellm, version: ">=1" } # version: FUTURE, unused
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```
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`system_dependencies` is exactly the `{kind: system}` case and is kept as an alias.
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Only encode a `requires` edge that is **not derivable** and that **castle itself
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must traverse** for an operation (status, bring-up order, group ops). Do **not**
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duplicate what another layer already owns — systemd `Requires=`/`After=` for unit
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ordering, uv/pnpm for build graphs. This is *castle's* slice, uncoupled from any
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one package ecosystem.
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### Env is derived *from* `requires`, never scraped *into* it
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Reading dependencies out of env strings is unstable (formats vary; a static
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frontend's API URL is baked into its bundle and invisible). The stable direction is
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the reverse: from an encoded `{kind: deployment}` requirement castle **generates**
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the wiring env — it knows the target's address (`<ref>.<domain>` / its port) and
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projects it into the consumer's env, optionally under the var named by `bind`. Same
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move as `${public_url}`, one step further. Dependency → env, never env → dependency.
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## Derived predicates
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Computed on demand from encoded `requires` + git + registry; nothing stored:
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- **`functional?`** — every `requires` is satisfied (system installed, deployment
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exists). The unmet ones *are* the node's status (`doctor`/`status`).
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- **`fresh?`** — the program's repo is at latest and clean (git status).
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- **`deployed?`** — the deployment is active in the registry.
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New predicates are just new functions over the same preconditions — there is
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nothing to "unify" in storage.
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## What's encoded vs derived (the whole surface)
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| datum | source | stored? |
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|-------|--------|---------|
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| repo / monorepo | git toplevel | derived |
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| `fresh?` / `deployed?` / `functional?` | git / registry / requires | derived |
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| env wiring for a dependency | the `requires` edge + target address | derived |
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| fan-in ("widely depended-on") | count of requires | derived |
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| a **non-derivable** requirement (frontend→backend, host package) | — | **encoded** (`requires`) |
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| the env var to bind a dep's URL to, when non-conventional | — | **encoded** (`requires[].bind`) |
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Every irreducible found so far is an **edge** (a relationship); no new **node**
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property has been needed yet — a sign the encoded surface stays tiny.
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