autolemetry-subscribers

Send events to multiple platforms

Subscribers for autolemetry to send events to PostHog, Mixpanel, Amplitude, Segment, and custom webhooks.

Why Use This?

Track once, send everywhere:

• Primary metrics → OpenTelemetry (infrastructure monitoring)
• Product events → PostHog / Mixpanel / Amplitude
• Customer data → Segment
• Custom integrations → Webhooks (Zapier, Make.com, etc.)

Zero overhead when not used: Adapters are optional. If you don't use them, they're tree-shaken out (0 bytes).

Building Custom Subscribers

Two base classes available:

EventSubscriber - Standard Base Class

Use for most custom subscribers. Provides production-ready features:

• Error handling (automatic catching + custom handlers)
• Pending request tracking (ensures delivery during shutdown)
• Graceful shutdown (drains pending requests)
• Enable/disable control (runtime toggle)

When to use: Any custom adapter (HTTP APIs, databases, webhooks, etc.)

import { EventSubscriber, EventPayload } from 'autolemetry-subscribers';

class MySubscriber extends EventSubscriber {
  readonly name = 'MySubscriber';

  protected async sendToDestination(payload: EventPayload): Promise<void> {
    // Send to your platform
    await fetch('https://api.example.com/events', {
      method: 'POST',
      body: JSON.stringify(payload)
    });
  }
}

StreamingEventSubscriber - For High-Throughput Streams

Extends EventSubscriber with batching and partitioning for streaming platforms.

When to use: Kafka, Kinesis, Pub/Sub, event streams, high-volume data pipelines

import { StreamingEventSubscriber } from 'autolemetry-subscribers';

class KafkaSubscriber extends StreamingEventSubscriber {
  readonly name = 'KafkaSubscriber';

  protected async sendBatch(events: EventPayload[]): Promise<void> {
    await this.producer.send({
      topic: 'events',
      messages: events.map(e => ({ value: JSON.stringify(e) }))
    });
  }
}

Installation

# Core package (required)
pnpm add autolemetry

# Subscribers package (optional)
pnpm add autolemetry-subscribers

# Install the events SDKs you need
pnpm add posthog-node      # For PostHog
pnpm add mixpanel          # For Mixpanel
pnpm add @segment/events-node  # For Segment
pnpm add @amplitude/events-node  # For Amplitude

Quick Start

Using Built-in Subscribers (Easiest)

Import subscribers directly from their entry points:

import { Events } from 'autolemetry/events';
import { PostHogSubscriber } from 'autolemetry-subscribers/posthog';
import { WebhookSubscriber } from 'autolemetry-subscribers/webhook';

const events = new Event('checkout', {
  subscribers: [
    new PostHogSubscriber({ apiKey: process.env.POSTHOG_API_KEY! }),
    new WebhookSubscriber({ url: 'https://your-webhook.com' })
  ]
});

// Sent to: OpenTelemetry + PostHog + Webhook
events.trackEvent('order.completed', { userId: '123', amount: 99.99 });

Your First Custom Subscriber (5 Minutes)

Create an adapter in 25 lines:

import { EventSubscriber, EventPayload } from 'autolemetry-subscribers';

class MySubscriber extends EventSubscriber {
  readonly name = 'MySubscriber';

  constructor(private apiKey: string) {
    super();
  }

  protected async sendToDestination(payload: EventPayload): Promise<void> {
    await fetch('https://your-api.com/events', {
      method: 'POST',
      headers: {
        'Authorization': `Bearer ${this.apiKey}`,
        'Content-Type': 'application/json'
      },
      body: JSON.stringify(payload)
    });
  }
}

// Use it!
const events = new Event('my-app', {
  subscribers: [new MySubscriber('your-api-key')]
});

That's it! Extend EventSubscriber and implement sendToDestination(). You get error handling, graceful shutdown, and pending request tracking automatically. See Your First Adapter Guide for details.

Test Your Adapter

import { AdapterTestHarness } from 'autolemetry-subscribers/testing';

const harness = new AdapterTestHarness(new MySubscriber('test-key'));
const results = await harness.runAll();

AdapterTestHarness.printResults(results);
// All tests passed! Your adapter is ready to use.

Add Middleware (Retry, Sampling, etc.)

import { applyMiddleware, retryMiddleware, samplingMiddleware } from 'autolemetry-subscribers/middleware';

const subscriber = applyMiddleware(
  new MySubscriber('api-key'),
  [
    retryMiddleware({ maxRetries: 3 }),  // Retry failed requests
    samplingMiddleware(0.1)               // Only send 10% of events
  ]
);

Built-in Adapters

PostHog

import { Events } from 'autolemetry/events';
import { PostHogSubscriber } from 'autolemetry-subscribers/posthog';

const events = new Event('checkout', {
  subscribers: [
    new PostHogSubscriber({
      apiKey: process.env.POSTHOG_API_KEY!,
      host: 'https://us.i.posthog.com' // optional
    })
  ]
});

// Sent to: OpenTelemetry + PostHog
events.trackEvent('order.completed', { 
  userId: '123', 
  amount: 99.99 
});

Mixpanel

import { MixpanelSubscriber } from 'autolemetry-subscribers/mixpanel';

const events = new Event('checkout', {
  subscribers: [
    new MixpanelSubscriber({
      token: process.env.MIXPANEL_TOKEN!
    })
  ]
});

Segment

import { SegmentSubscriber } from 'autolemetry-subscribers/segment';

const events = new Event('checkout', {
  subscribers: [
    new SegmentSubscriber({
      writeKey: process.env.SEGMENT_WRITE_KEY!
    })
  ]
});

Amplitude

import { AmplitudeSubscriber } from 'autolemetry-subscribers/amplitude';

const events = new Event('checkout', {
  subscribers: [
    new AmplitudeSubscriber({
      apiKey: process.env.AMPLITUDE_API_KEY!
    })
  ]
});

Webhook (Custom Integrations)

import { WebhookSubscriber } from 'autolemetry-subscribers/webhook';

const events = new Event('checkout', {
  subscribers: [
    new WebhookSubscriber({
      url: 'https://hooks.zapier.com/hooks/catch/...',
      headers: { 'X-API-Key': 'secret' },
      maxRetries: 3
    })
  ]
});

Multi-Platform Tracking

Send to multiple platforms simultaneously:

import { Events } from 'autolemetry/events';
import { PostHogSubscriber } from 'autolemetry-subscribers/posthog';
import { MixpanelSubscriber } from 'autolemetry-subscribers/mixpanel';
import { SegmentSubscriber } from 'autolemetry-subscribers/segment';

const events = new Event('checkout', {
  subscribers: [
    new PostHogSubscriber({ apiKey: 'phc_...' }),
    new MixpanelSubscriber({ token: '...' }),
    new SegmentSubscriber({ writeKey: '...' })
  ]
});

// Sent to: OpenTelemetry + PostHog + Mixpanel + Segment
events.trackEvent('order.completed', { 
  userId: '123', 
  amount: 99.99,
  currency: 'USD'
});

Delivery Patterns

Autolemetry-subscribers provides direct subscribers (fire-and-forget) - events are sent immediately to events platforms.

Direct Subscribers (Default)

Simple, fire-and-forget tracking - Events sent immediately to events platforms:

const events = new Event('app', {
  subscribers: [new PostHogSubscriber({ apiKey: '...' })]
})

// Events sent immediately, real-time
events.trackEvent('user.signup', { userId: '123' })
events.trackEvent('page.viewed', { path: '/checkout' })

Use for:

• Page views, button clicks, feature usage
• User behavior tracking
• High-volume, non-critical events
• Real-time events dashboards

Benefits:

• Simple, zero infrastructure
• Real-time delivery
• No database overhead
• Fire-and-forget

Trade-offs:

• Events can be lost if adapter/network fails
• No atomicity with database transactions

Transactional Outbox Pattern

For guaranteed delivery with atomicity, use the separate autolemetry-outbox package.

This provides:

• Guaranteed delivery (retries on failure)
• Atomicity with database state changes
• Fan-out to multiple destinations
• Requires database table + publisher worker
• Adds latency (1+ minute delay)

Install:

npm install autolemetry-outbox

Usage:

import { OutboxEventSubscriber } from 'autolemetry-outbox';
import { PostHogSubscriber } from 'autolemetry-subscribers/posthog';

const outbox = new DrizzleD1OutboxStorage(env.DB);
const events = new Event('checkout', {
  subscribers: [
    new OutboxEventSubscriber(outbox, { aggregateType: 'Order' })
  ]
});

Adapter Methods

All subscribers implement these methods:

interface EventSubscriber {
  // Track events
  trackEvent(name: string, attributes?: Record<string, any>): void;
  
  // Track conversion funnels
  trackFunnelStep(
    funnelName: string, 
    step: 'started' | 'completed' | 'abandoned' | 'failed',
    attributes?: Record<string, any>
  ): void;
  
  // Track business outcomes
  trackOutcome(
    operationName: string,
    outcome: 'success' | 'failure' | 'partial',
    attributes?: Record<string, any>
  ): void;
  
  // Track business values (revenue, counts, etc.)
  trackValue(
    name: string, 
    value: number,
    attributes?: Record<string, any>
  ): void;
}

Custom Subscriber

Create your own adapter for any platform:

import { EventSubscriber } from 'autolemetry/events-adapter';

class MyCustomSubscriber implements EventSubscriber {
  trackEvent(name: string, attributes?: Record<string, any>): void {
    // Send to your platform
    fetch('https://api.myplatform.com/events', {
      method: 'POST',
      body: JSON.stringify({ event: name, ...attributes })
    });
  }
  
  trackFunnelStep(funnel: string, step: string, attributes?: any): void {
    // Implement funnel tracking
  }
  
  trackOutcome(operation: string, outcome: string, attributes?: any): void {
    // Implement outcome tracking
  }
  
  trackValue(name: string, value: number, attributes?: any): void {
    // Implement value tracking
  }
}

// Use it
const events = new Event('app', {
  subscribers: [new MyCustomSubscriber()]
});

Configuration

Enable/Disable Adapters

const events = new Event('checkout', {
  subscribers: [
    new PostHogSubscriber({ 
      apiKey: 'phc_...',
      enabled: process.env.NODE_ENV === 'production' // Only in prod
    }),
    new MixpanelSubscriber({ 
      token: '...',
      enabled: false // Temporarily disabled
    })
  ]
});

Shutdown Gracefully

const posthog = new PostHogSubscriber({ apiKey: 'phc_...' });
const segment = new SegmentSubscriber({ writeKey: '...' });

// Before app shutdown
await posthog.shutdown();
await segment.shutdown();

Tree-Shaking

Adapters are fully tree-shakeable:

// Only PostHog code is bundled (not Mixpanel, Segment, etc.)
import { PostHogSubscriber } from 'autolemetry-subscribers/posthog';

Bundle sizes (gzipped):

• PostHog: ~8KB
• Mixpanel: ~6KB
• Segment: ~12KB
• Amplitude: ~10KB
• Webhook: ~2KB

Performance

Zero overhead when not used:

• If subscribers: [] (empty), no adapter code runs
• Tree-shaken out in production builds

Minimal overhead when used:

• Adapters only fire if added to the array
• Non-blocking (fire-and-forget)
• No impact on primary OpenTelemetry metrics

Middleware (Composition Patterns)

Add behaviors without modifying adapter code:

Available Middleware

import {
  applyMiddleware,
  retryMiddleware,          // Exponential backoff retry
  samplingMiddleware,       // Send only X% of events
  enrichmentMiddleware,     // Add fields to events
  loggingMiddleware,        // Debug events
  filterMiddleware,         // Only send matching events
  transformMiddleware,      // Transform events
  batchingMiddleware,       // Batch for efficiency
  rateLimitMiddleware,      // Throttle requests
  circuitBreakerMiddleware, // Prevent cascading failures
  timeoutMiddleware         // Add timeouts
} from 'autolemetry-subscribers/middleware';

Examples

Retry with Circuit Breaker:

const subscriber = applyMiddleware(
  new PostHogSubscriber({ apiKey: '...' }),
  [
    retryMiddleware({ maxRetries: 3, delayMs: 1000 }),
    circuitBreakerMiddleware({ failureThreshold: 5, timeout: 60000 })
  ]
);

Sample Events (Reduce Costs):

// Only send 10% of events
const subscriber = applyMiddleware(
  new WebhookSubscriber({ url: '...' }),
  [samplingMiddleware(0.1)]
);

Enrich Events:

const subscriber = applyMiddleware(
  adapter,
  [
    enrichmentMiddleware((event) => ({
      ...event,
      attributes: {
        ...event.attributes,
        environment: process.env.NODE_ENV,
        timestamp: Date.now()
      }
    }))
  ]
);

Batch Events:

const subscriber = applyMiddleware(
  adapter,
  [batchingMiddleware({ batchSize: 100, flushInterval: 5000 })]
);

Testing Custom Subscribers

AdapterTestHarness

Validate your adapter works correctly:

import { AdapterTestHarness } from 'autolemetry-subscribers/testing';

const harness = new AdapterTestHarness(new MySubscriber());
const results = await harness.runAll();

if (results.passed) {
  console.log('All tests passed!');
} else {
  console.error('Tests failed:', results.failures);
}

// Or use the built-in printer
AdapterTestHarness.printResults(results);

Tests include:

• Basic event tracking
• Funnel tracking
• Outcome tracking
• Value tracking
• Concurrent requests (50 events)
• Error handling
• Graceful shutdown

MockWebhookServer

Test webhook subscribers without real HTTP calls:

import { MockWebhookServer } from 'autolemetry-subscribers/testing';

const server = new MockWebhookServer();
const url = await server.start();

const subscriber = new WebhookSubscriber({ url });
await subscriber.trackEvent('test', { foo: 'bar' });

// Assert
const requests = server.getRequests();
expect(requests).toHaveLength(1);
expect(requests[0].body.event).toBe('test');

await server.stop();

Package Exports

All exports available:

// Import subscribers from their specific entry points
import { PostHogSubscriber } from 'autolemetry-subscribers/posthog';
import { MixpanelSubscriber } from 'autolemetry-subscribers/mixpanel';
import { SegmentSubscriber } from 'autolemetry-subscribers/segment';
import { AmplitudeSubscriber } from 'autolemetry-subscribers/amplitude';
import { WebhookSubscriber } from 'autolemetry-subscribers/webhook';
import { SlackSubscriber } from 'autolemetry-subscribers/slack';

// Base classes for building custom subscribers
import { EventSubscriber, EventPayload } from 'autolemetry-subscribers';
import { StreamingEventSubscriber } from 'autolemetry-subscribers';

// Middleware (composition)
import {
  applyMiddleware,
  retryMiddleware,
  samplingMiddleware,
  /* ... 8 more middleware functions */
} from 'autolemetry-subscribers/middleware';

// Testing utilities
import {
  AdapterTestHarness,
  MockWebhookServer,
  MockEventSubscriber
} from 'autolemetry-subscribers/testing';

// For outbox pattern, see autolemetry-outbox package

Resources

• Your First Adapter Guide - Create a custom adapter in 5 minutes
• Quickstart Template - Copy-paste 20-line template
• Testing Guide - Validate your adapter works
• Middleware Guide - Add retry, sampling, etc.
• Outbox Pattern - For transactional outbox pattern

Examples

See the autolemetry-examples package for complete examples.

License

MIT © Jag Reehal