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Export to PostHog

PostHog is a product analytics platform that helps you understand user behavior and debug issues. By exporting your Cloudflare Workers application telemetry to PostHog, you can:

  • Correlate logs with user sessions, events, and error tracking data
  • Query and filter logs by severity, attributes, and custom properties
  • Connect application logs to session replays for full debugging context
PostHog logs view with attributes expanded and a timeline view at the top

This guide will walk you through configuring your Cloudflare Worker application to export OpenTelemetry-compliant logs to PostHog.

Prerequisites

Before you begin, ensure you have:

  • An active PostHog account ↗ (free tier available)
  • A deployed Worker that you want to monitor
  • Your PostHog project API key

Step 1: Get your PostHog project API key

  1. Log in to your PostHog account ↗
  2. Navigate to the Project settings ↗
  3. Find your Project API key in the project details section
  4. Copy the API key - this is the same key used for capturing events and exceptions

The API key should look something like: phc_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Step 2: Determine your PostHog region endpoint

PostHog has different endpoints depending on your data region:

RegionLogs Endpoint
US (default)https://us.i.posthog.com/i/v1/logs
EUhttps://eu.i.posthog.com/i/v1/logs

You can find your region in your PostHog project settings or by checking the URL when logged into PostHog (either us.posthog.com or eu.posthog.com).

Step 3: Configure Cloudflare Logs destination

Now you'll create a destination in the Cloudflare dashboard that points to PostHog.

  1. Navigate to your Cloudflare account's Workers Observability ↗ section
  2. Click Add destination
  3. Configure your logs destination:
    • Destination Name: posthog-logs (or any descriptive name)
    • Destination Type: Select Logs
    • OTLP Endpoint: Your PostHog logs endpoint (e.g., https://us.i.posthog.com/i/v1/logs or https://eu.i.posthog.com/i/v1/logs)
    • Custom Headers: Add the authentication header:
      • Header name: Authorization
      • Header value: Bearer <your-project-api-key> (e.g., Bearer phc_xxxxx...)
  4. Click Save
Cloudflare destination configuration for PostHog logs with destination name, type selection, OTLP endpoint, and custom headers

Step 4: Configure your Worker

With your destination created in the Cloudflare dashboard, update your Worker's configuration to enable logs export.

JSONC
{
  "observability": {
    "logs": {
      "enabled": true,
      // Must match the destination name in the dashboard
      "destinations": ["posthog-logs"]
    }
  }
}

After updating your configuration, deploy your Worker for the changes to take effect.

Step 5: View logs in PostHog

Once your Worker is deployed and receiving traffic:

  1. Log in to your PostHog account ↗
  2. Navigate to the Logs section in the left sidebar
  3. Your Worker logs will appear with severity levels, timestamps, and attributes

You can filter logs by:

  • Severity level (trace, debug, info, warn, error, fatal)
  • Time range
  • Custom attributes added to your log entries
  • Keywords in log messages

Adding custom attributes to logs

You can add custom attributes to your logs using standard console methods with structured data:

JavaScript
export default {
  async fetch(request, env) {
    // Basic logging
    console.log("Processing request");


    // Logs with additional context
    console.info("User action", {
      userId: "user_123",
      action: "api_call",
      path: new URL(request.url).pathname
    });


    // Error logging with details
    console.error("Request failed", {
      error: "Connection timeout",
      retryCount: 3
    });


    return new Response("OK");
  }
};

These attributes will be searchable and filterable in the PostHog logs interface.

Troubleshooting

Logs not appearing in PostHog

  1. Verify your API key: Ensure you're using your project API key (starts with phc_), not a personal API key
  2. Check the endpoint region: Confirm you're using the correct regional endpoint (US or EU) matching your PostHog instance
  3. Confirm destination status: In the Cloudflare dashboard, verify your destination shows a recent successful delivery
  4. Check sampling rate: If you've configured a sampling rate, not all logs may be sent

Authentication errors

If you see authentication errors in your destination status:

  • Ensure the Authorization header value includes Bearer prefix followed by your API key
  • Verify the API key has not been revoked or regenerated in PostHog
  • Alternatively, you can pass the token as a query parameter by using https://us.i.posthog.com/i/v1/logs?token=<your-project-api-key> as your endpoint