docs/troubleshooting.md

   1 # Troubleshooting
   2
   3 ## My custom service card doesn't work, nothing appears or offline status is displayed (pi-hole, sonarr, ping, ...)
   4
   5 You might by facing a [CORS](https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS)
   6 (Cross Origin Request Sharing) issue. It happens when the targeted service is
   7 hosted on a different domain or port. Web browsers will not allow to fetch
   8 information from a different site without explicit permissions (the targeted
   9 service must include a special `Access-Control-Allow-Origin: *` HTTP headers).
  10 If this happens your web console (`ctrl+shift+i` or `F12`) will be filled with
  11 this kind of errors:
  12
  13 ```text
  14 Access to fetch at 'https://<target-service>' from origin 'https://<homer>' has
  15 been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present
  16 on the requested resource. If an opaque response serves your needs, set the
  17 request's mode to 'no-cors' to fetch the resource with CORS disabled.
  18 ```
  19
  20 To resolve this, you can either:
  21
  22 * Host all your target service under the same domain & port.
  23 * Modify the target server configuration so that the response of the server
  24 included following header- `Access-Control-Allow-Origin: *`
  25 (<https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS#simple_requests>). It
  26 might be an option in the targeted service, otherwise depending on how the
  27 service is hosted, the proxy or web server can seamlessly add it.
  28 * Use a cors proxy server like
  29 [`cors-container`](https://github.com/imjacobclark/cors-container),
  30 [`cors-anywhere`](https://github.com/Rob--W/cors-anywhere) or many others.