# Proxy with Flask

> Serve the MetricRaven script and events from a Flask app.

Source: https://metricraven.com/docs/proxy-flask  
Markdown: https://metricraven.com/docs/proxy-flask.md  
Section: Proxy

Two Flask routes relay the script and events with the requests library.

## Set it up

1. **Install requests**

   ```bash
   pip install requests
   ```

2. **Add the routes to your app**

   ```python title="metricraven_proxy.py"
   # metricraven_proxy.py · Flask 2.2+ with requests
   import requests
   from flask import Flask, Response, request

   app = Flask(__name__)
   # Behind a load balancer or CDN? Trust one proxy hop so remote_addr is the visitor:
   # from werkzeug.middleware.proxy_fix import ProxyFix
   # app.wsgi_app = ProxyFix(app.wsgi_app, x_for=1)

   def relay(url, cache_control):
       headers = {
           name: request.headers[name]
           for name in ("Content-Type", "Origin", "User-Agent")
           if name in request.headers
       }
       headers["X-Visitor-IP"] = request.remote_addr or ""
       try:
           upstream = requests.request(
               request.method,
               url,
               headers=headers,
               data=request.get_data() if request.method == "POST" else None,
               timeout=15,
           )
       except requests.RequestException:
           return Response(status=502)
       return Response(
           upstream.content,
           status=upstream.status_code,
           headers={
               "Content-Type": upstream.headers.get("Content-Type", "application/octet-stream"),
               "Cache-Control": cache_control,
           },
       )

   @app.get("/a/script")
   def metricraven_script():
       return relay("https://metricraven.com/js/script.js", "public, max-age=3600")

   @app.post("/a/event")
   def metricraven_event():
       return relay("https://metricraven.com/api/v1/collect", "no-store")
   ```

3. **Trust your load balancer, if any**

   Behind Nginx, Gunicorn on a platform router, or a CDN, `request.remote_addr` is that proxy. Enable the `ProxyFix` lines with the number of proxies in front of Flask.

4. **Point your script tag at your own paths**

   Replace your MetricRaven tag with this one. `src` loads the tracker from your domain and `data-api` sends its events there too.

   ```html title="Your website's shared layout"
   <script defer src="/a/script" data-api="/a/event" data-site-id="YOUR_SITE_ID"></script>
   ```

> **Verify it works**
>
> Open your live site. In the browser's Network panel, `/a/script` loads the tracker and `/a/event` answers with `ok: true`. Nothing goes to `metricraven.com` from the browser.
>
> In **Traffic**, your own visit should show your real country and city. If every visit appears to come from your server's or host's location, the visitor IP isn't being forwarded.

## Notes

- If a CDN or load balancer sits in front of this server, the connecting address is that proxy, not the visitor. Use the visitor IP header it sets (and only one it overwrites, so visitors can't fake it).

How the proxy works and which headers it must send: [Use your own domain](https://metricraven.com/docs/proxy).

## Details

- The proxy forwards only `Content-Type`, `Origin`, `User-Agent` and the visitor's IP as `x-visitor-ip`. Your site's cookies and auth headers never leave your server.
- `Origin` matters: MetricRaven checks it against your site's allowed domains. A missing or wrong origin is refused with `domain_not_allowed`.
- MetricRaven allows about 120 events per minute per visitor IP. Without `x-visitor-ip`, all of your visitors share the proxy's IP, so busy sites lose events as well as locations.
- A proxy doesn't guarantee that every blocker will allow tracking.