[Feat.] Enable grafana to show metrics (#4718)

Co-authored-by: zhaochenyang20 <zhaochen20@outlook.com>

examples/monitoring/README.md

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+# SGLang Monitoring Setup
+
+This directory contains a ready-to-use monitoring setup for SGLang using Prometheus and Grafana.
+
+## Prerequisites
+
+- Docker and Docker Compose installed
+- SGLang server running with metrics enabled
+
+## Usage
+
+1. Start your SGLang server with metrics enabled:
+
+```bash
+python -m sglang.launch_server --model-path meta-llama/Meta-Llama-3.1-8B-Instruct --port 30000 --enable-metrics
+```
+
+By default, the metrics server will run on `127.0.0.1:30000`.
+
+2. Start the monitoring stack:
+
+```bash
+cd examples/monitoring
+docker compose up
+```
+
+3. Access the monitoring interfaces:
+   - Grafana: [http://localhost:3000](http://localhost:3000)
+   - Prometheus: [http://localhost:9090](http://localhost:9090)
+
+Default Grafana login credentials:
+- Username: `admin`
+- Password: `admin`
+
+You'll be prompted to change the password on first login.
+
+4. The SGLang dashboard will be automatically available in the "SGLang Monitoring" folder.
+
+## Troubleshooting
+
+### Port Conflicts
+If you see errors like "port is already allocated":
+
+1. Check if you already have Prometheus or Grafana running:
+   ```bash
+   docker ps | grep -E 'prometheus|grafana'
+   ```
+
+2. Stop any conflicting containers:
+   ```bash
+   docker stop <container_id>
+   ```
+
+3. Ensure no other services are using ports 9090 and 3000:
+   ```bash
+   lsof -i :9090
+   lsof -i :3000
+   ```
+
+### Connection Issues
+If Grafana cannot connect to Prometheus:
+1. Check that both services are running
+2. Verify the datasource configuration in Grafana
+3. Check that your SGLang server is properly exposing metrics
+
+## Configuration
+
+- Prometheus configuration: `prometheus.yaml`
+- Docker Compose configuration: `docker-compose.yaml`
+- Grafana datasource: `grafana/datasources/datasource.yaml`
+- Grafana dashboard configuration: `grafana/dashboards/config/dashboard.yaml`
+- SGLang dashboard JSON: `grafana/dashboards/json/sglang-dashboard.json`
+
+## Customization
+
+You can customize the monitoring setup by modifying the configuration files as needed.