Metrics Exporters

Fasq provides a flexible metrics export system that allows you to send performance data to external monitoring systems, log files, or analytics platforms.

Overview

[!TIP] While Fasq provides built-in metrics support, we are developing the specialized fasq_metrics package for standardized Prometheus and OpenTelemetry exporting with zero configuration.

Metrics exporters enable you to:

Export performance data to console for debugging
Send metrics to JSON files for analysis
Integrate with OpenTelemetry-compatible observability platforms
Create custom exporters for your specific needs

Available Exporters

ConsoleExporter

Outputs metrics to the console in a human-readable format. Perfect for development and debugging.


import 'package:fasq/fasq.dart';
 
final client = QueryClient();
 
client.configureMetricsExporters(
  MetricsConfig(
    exporters: [ConsoleExporter()],
    enableAutoExport: true,
    exportInterval: Duration(minutes: 1),
  ),
);

JsonExporter

Exports metrics as JSON strings. Useful for logging systems or file-based analysis.


final client = QueryClient();
 
client.configureMetricsExporters(
  MetricsConfig(
    exporters: [
      JsonExporter(
        onExport: (jsonString) {
          // Write to file, send to API, etc.
          print(jsonString);
        },
      ),
    ],
    enableAutoExport: true,
    exportInterval: Duration(minutes: 1),
  ),
);

OpenTelemetryExporter

Sends metrics to OpenTelemetry-compatible backends using the OTLP protocol. Integrates with observability platforms like Prometheus, Grafana, or custom OTLP collectors.


final client = QueryClient();
 
client.configureMetricsExporters(
  MetricsConfig(
    exporters: [
      OpenTelemetryExporter(
        endpoint: 'https://your-otlp-collector.com/v1/metrics',
        headers: {
          'Authorization': 'Bearer your-token',
        },
      ),
    ],
    enableAutoExport: true,
    exportInterval: Duration(minutes: 1),
  ),
);

Configuration

MetricsConfig

The MetricsConfig class controls how and when metrics are exported:


final config = MetricsConfig(
  // List of exporters to use
  exporters: [ConsoleExporter(), JsonExporter()],
 
  // Enable automatic periodic export
  enableAutoExport: true,
 
  // How often to export (when auto-export is enabled)
  exportInterval: Duration(minutes: 1),
);

Auto-Export vs Manual Export

Auto-Export: Metrics are automatically exported at the specified interval.


client.configureMetricsExporters(
  MetricsConfig(
    exporters: [ConsoleExporter()],
    enableAutoExport: true,
    exportInterval: Duration(minutes: 1),
  ),
);

Manual Export: Trigger exports on-demand.


// Configure exporters (auto-export can be false)
client.configureMetricsExporters(
  MetricsConfig(
    exporters: [ConsoleExporter()],
    enableAutoExport: false,
  ),
);
 
// Export manually when needed
await client.exportMetricsManually();

Custom Exporters

You can create custom exporters by implementing the MetricsExporter interface:


class CustomExporter implements MetricsExporter {
  @override
  Future<void> export(PerformanceSnapshot snapshot) async {
    // Your custom export logic
    final data = snapshot.toJson();
 
    // Send to your monitoring system
    await sendToMonitoringSystem(data);
  }
}
 
// Use your custom exporter
client.configureMetricsExporters(
  MetricsConfig(
    exporters: [CustomExporter()],
    enableAutoExport: true,
  ),
);

Error Handling

Exporters are designed to be fault-tolerant. If one exporter fails, others continue to work:


client.configureMetricsExporters(
  MetricsConfig(
    exporters: [
      ConsoleExporter(),      // If this fails...
      JsonExporter(),         // ...this still works
      OpenTelemetryExporter(), // ...and this too
    ],
    enableAutoExport: true,
  ),
);

Errors in individual exporters are caught and logged, preventing one failure from stopping the entire export process.

Best Practices

Development: Use ConsoleExporter for quick debugging
Production: Use OpenTelemetryExporter or JsonExporter for structured logging
Testing: Use manual export (exportMetricsManually()) to verify exporter behavior
Performance: Adjust exportInterval based on your needs (more frequent = more overhead)

Example: Complete Setup


import 'package:fasq/fasq.dart';
 
void main() {
  final client = QueryClient(
    config: const CacheConfig(
      defaultStaleTime: Duration(minutes: 5),
    ),
  );
 
  // Configure metrics export
  client.configureMetricsExporters(
    MetricsConfig(
      exporters: [
        // Development: console output
        ConsoleExporter(),
 
        // Production: JSON logging
        JsonExporter(
          onExport: (json) {
            // Send to your logging service
            logToService(json);
          },
        ),
 
        // Observability: OpenTelemetry
        OpenTelemetryExporter(
          endpoint: 'https://otel-collector.example.com/v1/metrics',
        ),
      ],
      enableAutoExport: true,
      exportInterval: Duration(minutes: 1),
    ),
  );
 
  runApp(MyApp());
}