litellm-rs: Skill for Claude Code

Configuration Architecture Guide

Overview

LiteLLM-RS loads a single YAML file into type-safe Rust models (GatewayConfig in src/config/models/gateway.rs and its children), substitutes ${VAR} / $VAR tokens from the process environment during load, fills missing fields from serde defaults, then validates the whole tree once at startup.

There is no hot reload. Configuration is read once at startup; src/utils/config/optimized.rs states this explicitly ("Hot reload is not supported"). Restart the process to pick up changes. AppState.config (src/server/state.rs) is atomically swappable by explicit code paths, but nothing watches the file.

Load Order

┌─────────────────────────────────────────────────────────────────┐
│  1. YAML file                                                   │
│     --config PATH (default: "config/gateway.yaml", src/main.rs) │
└─────────────────────────────────────────────────────────────────┘
                              ↓
┌─────────────────────────────────────────────────────────────────┐
│  2. Environment substitution (substitute_env_vars)              │
│     ${VAR} = required (hard error if unset)                     │
│     $VAR   = best-effort (left literal if unset)                │
└─────────────────────────────────────────────────────────────────┘
                              ↓
┌─────────────────────────────────────────────────────────────────┐
│  3. serde parse + defaults                                      │
│     #[serde(default ...)] fills omitted fields;                 │
│     deny_unknown_fields rejects keys on structs that opt in     │
└─────────────────────────────────────────────────────────────────┘
                              ↓
┌─────────────────────────────────────────────────────────────────┐
│  4. Validation (Validate trait)                                 │
│     runs inside Config::from_file / Config::from_env            │
│     failure aborts startup                                      │
└─────────────────────────────────────────────────────────────────┘