any-hub/specs/004-modular-proxy-cache/data-model.md

Data Model: Modular Proxy & Cache Segmentation

Overview

The modular architecture introduces explicit metadata describing which proxy+cache module each hub uses, how modules register themselves, and what cache policies they expose. The underlying storage layout (StoragePath/<Hub>/<path>.body) remains unchanged, but new metadata ensures the runtime can resolve modules, enforce compatibility, and migrate legacy hubs incrementally.

Entities

1. HubConfigEntry

• Source: [[Hub]] blocks in config.toml (decoded via internal/config).
• Fields:
  • Name (string, required) – unique per config; used as hub identifier and storage namespace.
  • Domain (string, required) – hostname clients access; must be unique per process.
  • Port (int, required) – listen port; validated to 1–65535.
  • Upstream (string, required) – base URL for upstream registry; must be HTTPS or explicitly whitelisted HTTP.
  • Module (string, optional, default "legacy") – key resolved through module registry. Validation ensures module exists at load time.
  • CacheTTL, Proxy, and other overrides (optional) – reuse existing schema; modules may read these via dependency injection.
• Relationships:
  • HubConfigEntry.Module → ModuleMetadata.Key (many-to-one).
• Validation Rules:
  • Missing Module implicitly maps to legacy to preserve backward compatibility.
  • Changing Module requires a migration plan; config loader logs module name for observability.

2. ModuleMetadata

• Fields:
  • Key (string, required) – canonical identifier (e.g., npm-tarball).
  • Description (string) – human-readable summary.
  • SupportedProtocols ([]string) – e.g., HTTP, HTTPS, OCI.
  • CacheStrategy (CacheStrategyProfile) – embedded policy descriptor.
  • MigrationState (enum: legacy, beta, ga) – used for rollout dashboards.
  • Factory (function) – constructs proxy+cache handlers; not serialized but referenced in registry code.
• Relationships:
  • One ModuleMetadata may serve many hubs via config binding.

3. ModuleRegistry

• Representation: in-memory map maintained by internal/hubmodule/registry.go at process boot.
• Fields:
  • Modules (map[string]ModuleMetadata) – keyed by ModuleMetadata.Key.
  • DefaultKey (string) – legacy.
• Behavior:
  • Register(meta ModuleMetadata) called during init of each module package.
  • Resolve(key string) (ModuleMetadata, error) used by router bootstrap; errors bubble to config validation.
• Constraints:
  • Duplicate registrations fail fast.
  • Registry must export a list function for diagnostics (List()), enabling observability endpoints if needed.

4. CacheStrategyProfile

• Fields:
  • TTL (duration) – default TTL per module; hubs may override via config.
  • ValidationMode (enum: etag, last-modified, never) – defines revalidation behavior.
  • DiskLayout (string) – description of path mapping rules (default .body suffix).
  • RequiresMetadataFile (bool) – whether .meta entries are required.
  • SupportsStreamingWrite (bool) – indicates module can write cache while proxying upstream.
• Relationships:
  • Owned by ModuleMetadata; not independently referenced.
• Validation:
  • TTL must be positive.
  • Modules flagged as SupportsStreamingWrite=false must document fallback behavior before registration.

5. LegacyAdapterState

• Purpose: Tracks which hubs still run through the old shared implementation to support progressive migration.
• Fields:
  • HubName (string) – references HubConfigEntry.Name.
  • rolloutFlag (enum: legacy-only, dual, modular) – indicates traffic split for that hub.
  • FallbackDeadline (timestamp, optional) – when legacy path will be removed.
• Storage: In-memory map derived from config + environment flags; optionally surfaced via diagnostics endpoint.

State Transitions

1. Module Adoption

   • Start: HubConfigEntry.Module = "legacy".
   • Transition: operator edits config to new module key, runs validation.
   • Result: registry resolves new module, LegacyAdapterState updated to dual until rollout flag toggled fully.

2. Cache Strategy Update

   • Start: Module uses default TTL.
   • Transition: hub-level override applied in config.
   • Result: Module receives override via dependency injection and persists it in module-local settings without affecting other hubs.

3. Module Registration Lifecycle

   • Start: module package calls Register in its init().
   • Transition: duplicate key registration rejected; module must rename key or remove old registration.
   • Result: ModuleRegistry.Modules[key] available during server bootstrap.

Data Volume & Scale Assumptions

• Module metadata count is small (<20) and loaded entirely in memory.
• Hub count typically <50 per binary, so per-hub module resolution happens at startup and is cached.
• Disk usage remains the dominant storage cost; metadata adds negligible overhead.

Identity & Uniqueness Rules

• HubConfigEntry.Name and ModuleMetadata.Key must each be unique (case-insensitive) within a config/process.
• Module registry rejects duplicate keys to avoid ambiguous bindings.