---
phase: 01-foundation
plan: 03
subsystem: infra
tags: [yaml, pydantic, config, topology, parser]

requires:
  - phase: 01-02
    provides: "Pydantic v2 models (ToolResult, ErrorDetail) and server skeleton"
provides:
  - Dual-source config loading (YAML file + env vars with override priority)
  - Topology YAML parser with Pydantic validation and field-path error reporting
  - TopologySpec, NodeSpec, NetworkSpec, SshSpec, ExtraDisk, SnapshotDefaults models
affects: [phase-02, phase-03, phase-04]

tech-stack:
  added: []
  patterns: [dual-source-config, yaml-safe-load-only, validation-error-field-paths]

key-files:
  created:
    - vmcluster_mcp/config.py
    - vmcluster_mcp/topology/schema.py
    - vmcluster_mcp/topology/parser.py
    - tests/test_config.py
    - tests/test_topology.py
  modified: []

key-decisions:
  - "yaml.safe_load exclusively — never yaml.load (security)"
  - "Env vars override file values which override defaults"
  - "Topology validation errors include field path for clear debugging"
  - "config.py is a leaf module with zero internal imports"

patterns-established:
  - "Config priority: env vars > file values > Pydantic defaults"
  - "Topology loading: name → file path → yaml.safe_load → Pydantic validation → TopologySpec"
  - "Error reporting: ValidationError → ValueError with field paths"

requirements-completed: [FOUND-03, FOUND-04]

duration: 4min
completed: 2026-03-22
---

# Plan 01-03: Config + Topology Parser Summary

**Dual-source config loader and topology YAML parser with Pydantic validation completing all 4 foundation requirements.**

## What was built

**config.py** — Config model with 8 fields matching design doc section 2.6, load_config() that reads YAML from VMCLUSTER_CONFIG (or default path) then overlays VMCLUSTER_* env vars.

**topology/schema.py** — 6 Pydantic models matching design doc section 2.2: TopologySpec, NodeSpec, NetworkSpec, SshSpec, ExtraDisk, SnapshotDefaults.

**topology/parser.py** — load_topology(name, topology_dir) that loads and validates YAML, providing field-path error messages for invalid content.

## Verification

- 6 config tests pass (defaults, env vars, file loading, override priority)
- 14 topology tests pass (schema validation, defaults, parser happy/unhappy paths)
- 41 total tests pass across all Phase 1 modules
- ruff check passes
- yaml.safe_load used everywhere, no yaml.load present

## Self-Check: PASSED
