Remote Caddy reverse proxy returns 200 empty response

[kyeotic]

Describe the bug
Using Caddy (v2) as a reverse proxy I am unable to access the UI. Caddy is running on a different host than the change-detection.io docker container.

Version
Exact version in the top right area: 0.52.8

How did you install?

Docker compose

services:
    changedetection:
      image: ghcr.io/dgtlmoon/changedetection.io:0.52.8
      container_name: changedetection
      hostname: changedetection
      volumes:
        - changedetection-data:/datastore

      environment:
          - USE_X_SETTINGS=1
          - TZ=America/Los_Angeles
      networks:
        changenet:
          aliases:
            - changedetection-app
      restart: unless-stopped

volumes:
  changedetection-data:

networks:
  changenet:

Caddy

@change-detector host change-detector.local.kye.dev
	handle @change-detector {
		reverse_proxy 192.168.0.20:5000
	}

To Reproduce

Steps to reproduce the behavior:

1. Navigate to reverse proxy url
2. get white screen

OR

curl -I https://change-detector.local.kye.dev 
HTTP/2 200 
alt-svc: h3=":443"; ma=2592000
server: Caddy
date: Mon, 26 Jan 2026 19:33:45 GMT

Expected behavior
UI Should load

Additional context
Caddy is running on a different host than the change-detection docker container, reverse proxy using local network IP

[dgtlmoon]

Hello, sorry, this is not an issue directly with changedetection.io but you can find many good solutions here in the discussions https://github.com/dgtlmoon/changedetection.io/discussions?discussions_q=is%3Aopen+caddy also in the wiki section about caddy https://github.com/dgtlmoon/changedetection.io/wiki/Running-changedetection.io-behind-a-reverse-proxy#caddy-reverse-proxy

[kyeotic]

Ive gone over those and do not see a solution to this. I am already using the setup from the wiki caddy-section. This appears to be an isssue with the changedetection support for reverse proxies on remote hosts.

Using

curl -v   -H "Host: change-detector.local.kye.dev"   http://192.168.0.20:5000/

Returns the UI, and accessing the via http://192.168.0.20:5000/ works. Its only when caddy tries to reverse proxy that it fails.

I have also tried this more complete caddy config

@change-detector host change-detector.local.kye.dev
	handle @change-detector {
		reverse_proxy http://192.168.0.20:5000 {
			# Force headers exactly Flask expects
			header_up Host {host}
			header_up X-Forwarded-Host {host}
			header_up X-Forwarded-Port 443
			header_up X-Forwarded-Proto https
			header_up X-Forwarded-For {remote_host}
			# Disable HTTP/2 to avoid dropped responses
			transport http {
				versions 1.1
			}
		}
	}

[kyeotic]

@dgtlmoon Can you please re-open this? None of the links you provided have a solution; the first one actually has another unanswered caddy user

[dgtlmoon]

I'll plonk it in discussions until someone can point out that its a bug in CDIO, then i'll happily take it as an issue :)

[dgtlmoon]

Using Caddy (v2) as a reverse proxy I am unable to access the UI.

and

Its only when caddy tries to reverse proxy that it fails.

You dont mention what the error exactly is, output text, logs from the app at request time etc, it could help

[dgtlmoon]

@kyeotic This looks like the fix, but you need to give more information, what do you see in the CDIO container logs? and do you see any "Mixed Content" errors in either the CDIO container/instance, caddy or the browser?

The app has ProxyFix configured at /var/www/changedetection.io/changedetectionio/init.py:641-642:

app.wsgi_app = ProxyFix(app.wsgi_app, x_prefix=1, x_host=1)

But it's missing x_proto=1! This is critical when Caddy is proxying HTTPS→HTTP.

Why This Causes a White Screen

When the user accesses via https://change-detector.local.kye.dev:

1. Caddy receives: HTTPS request from browser
2. Caddy forwards: HTTP request to 192.168.0.20:5000 with X-Forwarded-Proto: https
3. Flask receives: HTTP request but ignores the X-Forwarded-Proto header (because x_proto is not enabled in ProxyFix)
4. Flask thinks: "This is an HTTP request"
5. Flask generates URLs: All url_for() calls generate http:// URLs
6. Browser receives: HTTPS page trying to load http:// resources (CSS, JS, etc.)
7. Browser blocks: Mixed content - HTTPS page cannot load HTTP resources
8. Result: White screen (HTML loads but no CSS/JS)

Additionally:

• CSRF tokens may fail due to protocol mismatch
• Socket.IO won't connect because the path will be wrong
• Session cookies may not work properly

The Fix

The ProxyFix line needs to be changed from:
app.wsgi_app = ProxyFix(app.wsgi_app, x_prefix=1, x_host=1)

To:
app.wsgi_app = ProxyFix(app.wsgi_app, x_prefix=1, x_host=1, x_proto=1)

This tells Flask to trust the X-Forwarded-Proto header that Caddy sets, so Flask will correctly generate https:// URLs when the original request was HTTPS.

How to Confirm This is the Issue

Ask the user to check their browser's Developer Console (F12):

• Network tab: Look for failed requests with mixed content errors
• Console tab: Look for "Mixed Content" warnings/errors
• View the page source and check if CSS/JS URLs are http:// instead of https://

so without this option (which i can add)

• Caddy is like someone telling you "hey, this came via HTTPS"
• x_proto=1 is Flask deciding "okay, I believe you"
• Without x_proto=1, Flask is like "I don't trust what you're saying, I'll just assume HTTP"

but let me know what the actual errors are that you see