I have encountered a similar problem. After using the proxy, the vite connection will be lost. Use HMR to specify the address. You can try it
server: { port: 3000, https: true, hmr: { host: 'yourhost.local', port: 3001, protocol: 'wss' } } }

Same problem with sveltekit. Note that the production build works.

The replication you provided, everything works fine with me, try the codesandbox you provided again, if it works, please provide a link to a repository that can replicate this issue.

Sorry, I had this problem when I tried again myself, I will look into it.

I'm having this issue as well, but I'm not sure if I'm just configuring something incorrectly.

I'm using a reverse proxy (ORY Oathkeeper) which does TLS termination and trying to run SvelteKit's dev server in a Docker container. The site loads in the browser, but I'm seeing the same [vite] server connection lost. polling for restart... client.ts:225:10 messages.

My svelte.config.js:

  kit: {
    target: '#svelte',
    vite: {
      server: {
	hmr: {
	  host: 'mydomain.org',
	  port: 443,
	  protocol: 'wss'
	}
      }
    }
  }

I feel like I've gone through every permutation of this config and Oathkeeper's to try to get this working, and have had no luck.

It's not clear to me what the correct configuration of everything should be. What I want is for SvelteKit / Vite to be listening behind Oathkeeper, not aware of TLS at all.

Should server.hmr.protocol be ws or wss? Even with ws set, the browser will use wss.

Is server.hmr.host only something you set when having Vite take care of HTTPS? If so, how can I tell Vite to make a client-side request to mydomain.org but that the server should simply listen on 0.0.0.0?

I've also found a server.hmr.clientPort config option which I've had no success with in getting this working.

@andrewbanchich Did you ever find a solution?

@jsjoeio Yes, this config got it working for us.

same issue, I'm trying to run vite on remote server on different url, vite itself runs on localhost:3000 over https

Ok, I've managed to resolve it for myself. I've had to define host where vite is running, because by default it's taken from window.location.hostname, so that's why it never connects.

hmr: {
    host: 'localhost'
}

@jsjoeio Yes, this config got it working for us.

thanks! clientPort did the trick for me.

I think the core issue is the same as #4259. Let's keep the conversation there.