Fan-out to Multiple Backends

Ship logs to both FlareLog and any OTLP-compatible backend simultaneously.

Why Fan-out?

Fan-out allows you to:

• Migrate gradually — Ship to both old and new backends during transition
• Redundancy — Have multiple copies of your observability data
• Different tools for different teams — FlareLog for developers, Grafana for ops
• Cost optimization — Use different backends for different data types

Configuration

Use the transports array to configure multiple backends:

import { flarelog } from "@flarelog/sdk";

const logger = flarelog({
  transports: [
    { type: "console" },
    { type: "flarelog", apiKey: process.env.FLARELOG_API_KEY },
    {
      type: "otlp",
      endpoint: process.env.OTEL_EXPORTER_OTLP_ENDPOINT,
    },
  ],
});

Environment Variables

You can also use environment variables for fan-out:

# .env
FLARELOG_API_KEY=fl_your_api_key
OTEL_EXPORTER_OTLP_ENDPOINT=https://otlp-gateway-prod-eu-west-0.grafana.net
OTEL_EXPORTER_OTLP_HEADERS=Authorization=Basic\ base64token

const logger = flarelog({});
// Auto-detects both FLARELOG_API_KEY and OTEL_EXPORTER_OTLP_ENDPOINT
// Ships to both backends + console

Common Backends

Grafana Cloud

const logger = flarelog({
  transports: [
    { type: "flarelog", apiKey: process.env.FLARELOG_API_KEY },
    {
      type: "otlp",
      endpoint: "https://otlp-gateway-prod-eu-west-0.grafana.net",
      headers: {
        Authorization: "Basic " + btoa(`${GRAFANA_INSTANCE_ID}:${GRAFANA_API_KEY}`),
      },
    },
  ],
});

Honeycomb

const logger = flarelog({
  transports: [
    { type: "flarelog", apiKey: process.env.FLARELOG_API_KEY },
    {
      type: "otlp",
      endpoint: "https://api.honeycomb.io/v1/traces",
      headers: {
        "x-honeycomb-team": process.env.HONEYCOMB_API_KEY,
      },
    },
  ],
});

Datadog

const logger = flarelog({
  transports: [
    { type: "flarelog", apiKey: process.env.FLARELOG_API_KEY },
    {
      type: "otlp",
      endpoint: "https://trace.agent.datadoghq.com/api/v0.2/traces",
      headers: {
        "DD-API-KEY": process.env.DD_API_KEY,
      },
    },
  ],
});

Selective Fan-out

Use beforeSend to route different logs to different backends:

const logger = flarelog({
  transports: [
    { type: "flarelog", apiKey: process.env.FLARELOG_API_KEY },
    {
      type: "otlp",
      endpoint: process.env.OTEL_EXPORTER_OTLP_ENDPOINT,
    },
  ],
  beforeSend: (log) => {
    // Add backend routing hint
    if (log.level === "ERROR" || log.level === "FATAL") {
      log.metadata = { ...log.metadata, _route: "all" };
    }
    return log;
  },
});

Performance Considerations

• Each transport adds network overhead
• Consider using sampleRate to reduce volume for high-traffic apps
• Use workerMode: true in serverless environments to flush immediately

Troubleshooting

Logs not appearing in one backend

1. Check that the backend endpoint is correct
2. Verify API keys and headers
3. Enable debug: true to see transport diagnostics
4. Check network connectivity from your environment