Hey there! We've found the following might help you get unblocked faster:

• 🧵 502 Bad Gateway Error

• 🧵 I am experiencing a persistent 502 Bad Gateway error on my web application service.

• 🧵 502 bad gateway error

If you find the answer from one of these, please let us know by solving the thread!

Hi Lance,

just to double-check — did you also set the port in your public domain configuration, or only as an environment variable? Sometimes Railway expects the port to be explicitly linked in the custom domain settings as well, not just defined in PORT in your service environment variables.

Regarding your questions at the end:

• Yes, it’s worth testing with Railway’s default domain first to confirm the service itself is reachable before troubleshooting the custom domain

The persistent 502 Bad Gateway error, despite your application starting correctly, almost always points to a health check failure. Your app is running, but Railway's proxy can't get a successful confirmation that it's ready to receive traffic, so it doesn't route requests to it.

## The Most Likely Cause: Health Check Mismatch

Your application is running successfully inside the container, but Railway's edge proxy, which sits between the public internet and your service, needs to verify your app is "healthy" before it sends user traffic your way. By default, it does this by sending a request to the root path (/).

If your root path (/) takes too long to respond (e.g., it needs to load a model or query the database) or doesn't return a 2xx status code quickly, the health check will fail. The proxy then assumes your app is down and returns a 502 Bad Gateway.

You've already created a /health endpoint in your Flask app, which is the perfect solution. Now you just need to tell Railway to use it.

How to Fix It

1. Go to your project in the Railway dashboard.

2. Click on your chatmaps-mvp service to open its settings.

3. Go to the Networking tab.

4. In the "Healthcheck" section, find the Healthcheck Path input field.

5. Enter the path to your dedicated health endpoint: /health.

6. Click "Save Changes" and trigger a new deployment.

This tells Railway's proxy to ping the simple and fast /health endpoint instead of the potentially slow / endpoint. Since your /health route returns a quick 200 OK, the health checks will pass and the proxy will begin routing traffic to your container.

## Secondary Checks

If updating the health check path doesn't resolve it, here are the next steps.

Custom Domain vs. Default Domain

You asked if you should test with Railway's default domain. Yes, absolutely. This is a critical debugging step.

• Try accessing your service using its default *.up.railway.app URL (you can find this in the Networking tab).

• If the default URL works: The problem is with your custom domain's DNS configuration. Ensure your CNAME record for chatmaps.ai is pointing correctly to Railway's provided hostname (public.railway.app or similar) at your domain registrar.

• If the default URL also fails: The problem is definitely the health check or another internal configuration issue.

Streamlit's Specific Needs

While your Procfile is set up for Flask/Gunicorn, it's worth noting that Streamlit has its own server requirements and sometimes behaves differently regarding health checks. If you switch back to Streamlit, ensure your start command is correct and that the health check endpoint is still valid. A common start command for Streamlit is:

Bash

streamlit run app.py --server.port $PORT --server.address 0.0.0.0

## Helpful Articles & Documentation

Here are some official Railway docs that directly address this situation. Reading through them will provide more context.

• Railway Docs: Health Checks: This is the most relevant article. It explains exactly how the process works and why failures lead to 502 errors.

• Railway Docs: Custom Domains: A good resource to double-check your DNS settings if you find that the default domain works but your custom one doesn't.

• Railway Docs: Debugging: This guide provides a general overview of troubleshooting common deployment problems, including 502 errors.

In summary, your debugging has been excellent. You've correctly isolated the problem to the connection between the proxy and your container. The final step is likely just telling the proxy which door to knock on (/health) to see if your app is home.

The issue was needing to set the manual port in Railway's network settings. Thanks so much for your help with this.