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) (Cross Origin Request Sharing) issue.
   6 It happens when the targeted service is hosted on a different domain or port.
   7 Web browsers will not allow to fetch information from a different site without explicit permissions (the targeted service
   8 must include a special `Access-Control-Allow-Origin: *` HTTP headers).
   9 If this happens your web console (`ctrl+shit+i` or `F12`) will be filled with this kind of errors:
  10
  11 ```text
  12 Access to fetch at 'https://<target-service>' from origin 'https://<homer>' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.
  13 ```
  14
  15 To resolve this, you can either:
  16
  17 * Host all your target service under the same domain & port.
  18 * Modify the target sever configuration so that the response of the server included following header- `Access-Control-Allow-Origin: *` (<https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS#simple_requests>). It might be an option in the targeted service, otherwise depending on how the service is hosted, the proxy or web server can seamlessly add it.
  19 * Use a cors proxy sever like [`cors-container`](https://github.com/imjacobclark/cors-container), [`cors-anywhere`](https://github.com/Rob--W/cors-anywhere) or many others.