LegCo Reranker

RAG-powered document Q&A app. Upload PDFs, ask questions in Cantonese, get bullet-point answers with citations.

Quick Start (Dev)

# Backend
cd backend
cp .env.example .env    # edit .env with your LLM API key
pip install -r requirements.txt
uvicorn app.main:app --host 0.0.0.0 --port 8000 --reload

# Frontend
cd frontend
npm install
npm run dev

Backend → http://localhost:8000 | Frontend → http://localhost:5173

Deploy with Docker

Prerequisites

• Docker 24+ and Docker Compose v2
• OpenRouter API key (or compatible LLM provider)

Setup

# 1. Configure environment
cp backend/.env.example backend/.env
# Edit backend/.env with your API keys and model names

# 2. Build and start
docker compose up -d --build

# 3. Check health
curl http://localhost:8000/health

The app is served at http://localhost:8000 — both the API and the frontend UI.

Volumes

Volume	Purpose
chroma_data	ChromaDB vector store (persistent)
chunk_data	Extracted PDF page files
sqlite_data	Prompt templates and query history

Environment Variables

All configurable via backend/.env:

Variable	Default	Description
LLM_BASE_URL	https://openrouter.ai/api/v1	LLM API endpoint
LLM_API_KEY	—	API key for LLM provider
LLM_MODEL_NAME	qwen/qwen3.5-35b-a3b	Chat model
LLM_TIMEOUT	60.0	LLM request timeout in seconds
LLM_ENABLE_THINKING	false	Enable LLM thinking/reasoning tokens
VLLM_ENGINE	false	Use vLLM-format extra_body instead of OpenRouter
EMBEDDING_MODEL	qwen/qwen3-embedding-4b	Embedding model
EMBEDDING_BASE_URL	https://openrouter.ai/api/v1	Embedding API endpoint
EMBEDDING_API_KEY	—	API key for embeddings (falls back to LLM_API_KEY)
CHROMA_DB_PATH	./chroma_db	ChromaDB persistent storage
CHUNK_SIZE	1000	Token chunk size
CHUNK_OVERLAP	200	Token chunk overlap
RETRIEVAL_N_RESULTS	10	Chunks per sub-question
RELEVANCE_THRESHOLD	7.0	Min relevance score (0-10)
PROMPTS_DB_PATH	./data/prompts.db	Prompt templates SQLite
HISTORY_DB_PATH	./data/history.db	Query history SQLite
CORS_ORIGINS	["http://localhost:5173","http://localhost:3000"]	Allowed CORS origins

Production: Nginx Reverse Proxy

# Include nginx.conf in your site config
# Key settings:
# - client_max_body_size 350M   (allow large PDF uploads)
# - proxy_read_timeout 300s     (LLM calls can take minutes)

# Install nginx
sudo apt install nginx

# Copy config
sudo cp nginx.conf /etc/nginx/sites-available/legco
sudo ln -s /etc/nginx/sites-available/legco /etc/nginx/sites-enabled/
sudo nginx -t && sudo systemctl reload nginx

Stopping

docker compose down

Updating

git pull
docker compose up -d --build

Cross-Platform Build (aarch64 → amd64)

When building on an aarch64/ARM64 machine (Apple Silicon, ARM Windows WSL2, Raspberry Pi) for deployment to an x86_64/amd64 server:

1. Install buildx

# Download buildx for arm64
BUILDX_VERSION=$(wget -qO- https://api.github.com/repos/docker/buildx/releases/latest | grep tag_name | head -1 | cut -d'"' -f4)
wget "https://github.com/docker/buildx/releases/download/${BUILDX_VERSION}/buildx-${BUILDX_VERSION}.linux-arm64" -O ~/.docker/cli-plugins/docker-buildx
chmod +x ~/.docker/cli-plugins/docker-buildx

2. Register QEMU for amd64 emulation

docker run --privileged --rm tonistiigi/binfmt --install all

3. Build for amd64

DOCKER_BUILDKIT=1 docker build --platform linux/amd64 -t legco_reranker:amd64 .

4. Export and transfer to server

# Save image to tar file
docker save legco_reranker:amd64 -o legco_reranker_amd64.tar

# Compress (~762MB → ~250MB)
gzip legco_reranker_amd64.tar

# Transfer to server
scp legco_reranker_amd64.tar.gz user@server:/path/

# On the x86_64 server:
gunzip legco_reranker_amd64.tar.gz
docker load -i legco_reranker_amd64.tar

# Run
docker run -d --name legco -p 80:8000 --env-file backend/.env \
  -v chroma_data:/app/chroma_db \
  -v chunk_data:/app/document_chunk \
  -v sqlite_data:/app/data \
  legco_reranker:amd64

5. Test run (local, port 8888)

Before transferring to the server, test the amd64 image locally. Pass all config inline (no --env-file):

docker run -d --name legco_test -p 8888:8000 \
  -e LLM_BASE_URL=https://openrouter.ai/api/v1 \
  -e LLM_API_KEY=your_key_here \
  -e LLM_MODEL_NAME=qwen/qwen3.6-35b-a3b \
  -e LLM_TIMEOUT=60.0 \
  -e LLM_ENABLE_THINKING=false \
  -e VLLM_ENGINE=false \
  -e EMBEDDING_MODEL=qwen/qwen3-embedding-4b \
  -e EMBEDDING_BASE_URL=https://openrouter.ai/api/v1 \
  -e EMBEDDING_API_KEY=your_key_here \
  -e CHROMA_DB_PATH=./chroma_db \
  -e CHUNK_SIZE=1000 \
  -e CHUNK_OVERLAP=200 \
  -e RETRIEVAL_N_RESULTS=10 \
  -e RELEVANCE_THRESHOLD=7.0 \
  -e PROMPTS_DB_PATH=./data/prompts.db \
  -e HISTORY_DB_PATH=./data/history.db \
  -e CORS_ORIGINS='["http://localhost:5173","http://localhost:3000"]' \
  -v ~/woody/legco/data/chroma_db:/app/chroma_db \
  -v ~/woody/legco/data/document_chunk:/app/document_chunk \
  -v ~/woody/legco/data/data:/app/data \
  legco_reranker:amd64

# Verify
curl http://localhost:8888/health

# Clean up
docker rm -f legco_test

Architecture

User → Nginx (80) → Uvicorn (8000)
                         ├── FastAPI API (/api/v1/*)
                         └── Static Frontend (/*)
                              └── React 18 + Vite + Tailwind

RAG Pipeline (Per-Sub-Question)

User Question
  → [LLM] Decompose into 2-5 sub-questions
  → [ChromaDB] Retrieve 10 chunks per sub-question
  → [LLM] Score all chunks against their own sub-question (single call)
  → [LLM] Generate markdown response per sub-question
  → SSE stream with per-sub-question sources

Notes

• PDF upload limit: 300MB
• Desktop only (not mobile-optimized)
• No authentication (public demo)
• All LLM calls routed through configurable base URL