update

docs/DATABASE_SCHEMA.md

@@ -269,3 +269,68 @@ db.articles.find({ summary: { $exists: false } })
 // Count summarized articles
 db.articles.countDocuments({ summary: { $exists: true, $ne: null } })
 ```
+
+
+---
+
+## MongoDB Connection Configuration
+
+### Docker Compose Setup
+
+**Connection URI:**
+```env
+MONGODB_URI=mongodb://admin:changeme@mongodb:27017/
+```
+
+**Key Points:**
+- Uses `mongodb` (Docker service name), not `localhost`
+- Includes authentication credentials
+- Only works inside Docker network
+- Port 27017 is NOT exposed to host (internal only)
+
+### Why 'mongodb' Instead of 'localhost'?
+
+**Inside Docker containers:**
+```
+Container → mongodb:27017 ✅ Works (Docker DNS)
+Container → localhost:27017 ❌ Fails (localhost = container itself)
+```
+
+**From host machine:**
+```
+Host → localhost:27017 ❌ Blocked (port not exposed)
+Host → mongodb:27017 ❌ Fails (DNS only works in Docker)
+```
+
+### Connection Priority
+
+1. **Docker Compose environment variables** (highest)
+2. **.env file** (fallback)
+3. **Code defaults** (lowest)
+
+### Testing Connection
+
+```bash
+# From backend
+docker-compose exec backend python -c "
+from database import articles_collection
+print(f'Articles: {articles_collection.count_documents({})}')
+"
+
+# From crawler
+docker-compose exec crawler python -c "
+from pymongo import MongoClient
+from config import Config
+client = MongoClient(Config.MONGODB_URI)
+print(f'MongoDB version: {client.server_info()[\"version\"]}')
+"
+```
+
+### Security
+
+- ✅ MongoDB is internal-only (not exposed to host)
+- ✅ Uses authentication (username/password)
+- ✅ Only accessible via Docker network
+- ✅ Cannot be accessed from external network
+
+See [SECURITY_NOTES.md](SECURITY_NOTES.md) for more security details.