Real-time chat with group room and 1-to-1 DMs, built using FastAPI + WebSockets, Redis pub/sub (for fan-out & presence), and PostgreSQL (for message history). Frontend is plain HTML/CSS/JS with Jinja templates. Dockerized for easy local runs; CI/CD-friendly for cloud deploys.

Live demo: https://chat-with-randoms.onrender.com/

• 🚪 Registration (18+), globally unique username (inline “name taken” warning)
• 👥 Online presence synced via Redis (works across instances)
• 💬 General room + Direct Messages (DMs)
• 📚 Message history persisted in Postgres
• 🔔 Unread badges (red counters) for rooms/DMs
• ♻️ Local cache per conversation (so messages persist when switching tabs)
• 🐳 Dockerized; one command local up via Compose
• 🔁 Auto-deploy ready (link repo to host = redeploy on every push)

FastAPI (WebSockets) ├─ Manages WS connections per instance ├─ Publishes to Redis channels (messages & presence) └─ Subscribes to Redis to fan-out to local sockets

Redis (Upstash in prod) ├─ Channels: chat_messages:* , user_status_channel └─ Keys: online_users_set (presence), user_profiles (name→profile)

PostgreSQL (Render in prod) └─ Stores message history

. ├─ backend/ │ ├─ main.py # FastAPI app (WS, Redis pub/sub, DB) │ ├─ Dockerfile # Container image for backend │ ├─ requirements.txt │ └─ static/ # Frontend (templates + CSS) │ ├─ index.html # registration page │ ├─ chat.html # chat UI + client logic │ └─ style.css ├─ docker-compose.yml # local dev (backend + redis + postgres) └─ init_db.sql # schema for messages table & index

• Docker Desktop (or Docker + Docker Compose)
• Ports 8000, 6379, 5432 available

# 1) clone
git clone <your-repo-url>
cd <your-repo>

# 2) start services
docker compose up --build

.

🔌 Endpoints GET / — registration page POST /register — saves cookie, redirects to /chat GET /chat — chat UI GET /messages/{room_id}?limit=50 — recent messages (room or DM roomId) GET /online_users — currently online users GET /api/name_available?name=... — username availability WS /ws/{user_id} — WebSocket channel

🙌 Credits FastAPI Uvicorn Redis(Upstash in production) PostgreSQL Docker