The PostHog Proxy Saga - A Journey Through Simple Implementation Hell

You know that feeling when you think a feature is going to be a quick afternoon task, and then days later you're deep in debugging hell? Yeah, that was me implementing a PostHog reverse proxy.

A "Simple" Plan

The story begins like all good software development tragedies: with overconfidence. PostHog's reverse proxy documentation makes setting up a reverse proxy sound like a breeze - and it is, if you're using one of the methods covered in their guides. A reverse proxy enables you to send events to PostHog Cloud using your own domain, which means events are less likely to be intercepted by tracking blockers. Sounds straightforward, right?

"How hard could it be?" I thought, cracking my knuckles. "It's just routing some requests through our domain instead of directly to PostHog. I'll have this wrapped up before lunch."

Narrator voice: She did not have it wrapped up before lunch.

Initial Implementation

Started strong! I set up the basic reverse proxy structure, added the routes, and configured the headers. The initial implementation was actually pretty clean - PostHog requires that the proxy sets the Host header to the same host it's calling, so I made sure to handle that properly.

The main implementation included a dedicated posthog-proxy.ts file for handling all the proxy logic, proper header forwarding and Host header rewriting, integration with our existing Express.js setup, and Firebase configuration updates for deployment.

Everything looked good in local testing. Time to deploy!

Welcome to CORS Hell

And then reality hit like a truck full of HTTP 400 errors.

CORS issues. CORS issues everywhere. You know that scene in The Matrix where Neo sees the code for the first time? That was me looking at browser dev tools, except instead of green cascading characters, it was angry red CORS warnings.

The proxy was working... sort of. Sometimes. For some requests. When the wind was blowing in the right direction and I sacrificed the appropriate amount of coffee to the deployment gods.

Troubleshooting Descent

By this point, I was troubleshooting everything. I added logging to every function, endpoint, and error handler I could think of. The irony wasn't lost on me that I was sending more debug events to PostHog than actual user events.

Each iteration was me trying a slightly different approach, like a developer version of throwing spaghetti at the wall to see what sticks. Except the wall was made of CORS policies and the spaghetti was my rapidly diminishing sanity.

Dynamic Environment Rabbit Hole

Just when I thought I had CORS figured out, I realized I needed to handle different environments dynamically. The proxy needed to work seamlessly whether someone was developing on localhost:3000, localhost:5000, or our staging and production domains.

This meant building environment detection logic to determine the correct origin, dynamic CORS origin configuration based on the current environment, different proxy endpoints for local development vs. production, and making sure the Host header manipulation worked across all scenarios.

What started as a simple proxy was becoming a complex environment-aware routing system. I found myself writing conditional logic for every possible deployment scenario, trying to account for every edge case a developer might encounter.

The code was getting increasingly complex, with nested conditionals and environment-specific configurations that made debugging even harder.

Simplification Salvation

Sometimes the solution isn't more complex configuration - it's less. After several rounds of adding layers of complexity, I finally stepped back and asked the magic question: "What if I just... made it simpler?"

Instead of trying to handle every possible environment dynamically, I stripped it down to the essentials: a basic proxy that forwards requests to PostHog, standard CORS configuration that works across environments, and simple environment variable setup for the few things that actually needed to be dynamic.

And you know what? It worked. The simplified version handled everything the complex version was trying to do, but without all the elaborate environment detection and conditional logic that was causing issues.

Reality Check

Let's break down what this "simple" proxy implementation actually involved:

• Multiple iterations: Numerous attempts at different approaches
• Several pull requests: Main implementation plus follow-up fixes
• Extended timeline: What should have been an afternoon turned into several days
• Coffee consumed: Approximately 47 cups
• Expletives muttered: Classified

What We Actually Built

The final implementation includes a clean TypeScript proxy service that handles PostHog API routes, proper CORS configuration (after much trial and error), environment variable management for different deployment stages, Firebase Function integration for serverless deployment, and documentation that will hopefully save future developers from this journey.

Lessons Learned (The Hard Way)

1. "Simple" is relative: What looks simple in documentation often has hidden complexity in implementation.
2. CORS will humble you: No matter how experienced you are, CORS configuration will find new ways to surprise you.
3. Don't over-engineer environments: Trying to handle every possible localhost port and development scenario dynamically just creates more problems than it solves.
4. Document your pain: Future you (and your teammates) will thank you for leaving breadcrumbs through the debugging maze.
5. Keep it simple: When you're deep in complexity, the answer is usually to strip away unnecessary features, not add more.

Silver Lining

Despite the journey, we now have a robust PostHog proxy that bypasses ad blockers for better analytics data capture, runs reliably in our Firebase Cloud Functions environment, has proper error handling and logging, and actually works (shocking, I know).

And hey, I now know more about reverse proxy configuration than I ever wanted to. That's got to count for something on my developer resume, right?

For Future Implementers

If you're thinking about implementing a PostHog reverse proxy (or any reverse proxy, really), here's my hard-won advice:

1. Start simple and stay simple: Resist the urge to handle every edge case from day one
2. Don't overthink localhost: Your developers can handle setting a consistent local port - you don't need to auto-detect everything
3. CORS is your frenemy: Understand it, respect it, fear it appropriately
4. Use PostHog's managed proxy if you can: PostHog's managed reverse proxy service enables you to route traffic through PostHog's infrastructure, simplifying the deployment and management - seriously, consider paying for this convenience
5. When in doubt, simplify: If your proxy code has more conditionals than your business logic, you've probably gone too far

Aftermath

Was it worth it? Absolutely. We're now capturing way more user analytics data, our tracking is more reliable, and we have complete control over the implementation. Plus, I have a great story for tech meetups.

Would I do it again? Ask me after I've had more coffee.