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[Docs] [Router] Update Observability and Common Issues Section (#11302)

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Wenyi Xu
2025-10-07 23:03:09 +08:00
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docs/advanced_features/router.md
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@@ -421,13 +421,31 @@ python -m sglang_router.launch_router \
--request-id-headers x-request-id x-trace-id
```
## Observability
When Prometheus is enabled, the router provides several key metrics for observability.
| Metric Name | Type | Description |
|:---------------------------------------|:----------|:-----------------------------------------------------------------------------------------------------|
| `sgl_router_requests_total` | Counter | Total number of requests received by the router's API endpoint. Useful for tracking overall traffic. |
| `sgl_router_processed_requests_total` | Counter | Total requests processed, labeled by `worker`. Critical for spotting load imbalances. |
| `sgl_router_active_workers` | Gauge | The current number of healthy workers in the routing pool. Essential for alerting. |
| `sgl_router_running_requests` | Gauge | The number of currently in-flight requests, labeled by `worker`. For monitoring real-time load. |
| `sgl_router_cache_hits_total` | Counter | Total requests routed to a worker with a matching prefix cache. |
| `sgl_router_cache_misses_total` | Counter | Total requests that could not be routed based on cache locality. |
| `sgl_router_generate_duration_seconds` | Histogram | Tracks end-to-end request latency. Use this to monitor performance (e.g., p95/p99). |
## Troubleshooting
### Common Issues
1. **Workers not connecting**: Ensure workers are fully initialized before starting the router. Use `--worker-startup-timeout-secs` to increase wait time.
2. **High latency**: Check if cache-aware routing is causing imbalance. Try adjusting `--balance-abs-threshold` and `--balance-rel-threshold`.
2. **High latency**:
- **A common cause**: Load Imbalanced.
- Check the `sgl_router_processed_requests_total` metric grouped by `worker`.
- Cache-aware routing might be prioritizing cache hits too aggressively.
- Try adjusting `--balance-abs-threshold` and `--balance-rel-threshold`.
3. **Memory growth**: Reduce `--max-tree-size` or decrease `--eviction-interval-secs` for more aggressive cache cleanup.