Reverse Proxy with Caddy shows blank page

Support
1

I am trying to access the GUI for the syncthing instance running on my headless orangepi from other devices on my LAN by reverse proxying with caddy.

  • reloaded syncthing with default configuration
    • added gui name + pw
    • added folder
    • connected device
  • attempting caddy with caddyv2 config provided in syncthing docs
  • ~$ sudo -E caddy run --config syncthing2.caddy --adapter caddyfile
 2025/09/25 13:19:48.281 INFO    using provided configuration    {“config_file”: “syncthing2.caddy”, “config_adapter”: “caddyfile”}
 2025/09/25 13:19:48.286 WARN    caddyfile       Using a path in a site address is deprecated; please use the ‘handle’ directive instead       {“address”: “”}
 2025/09/25 13:19:48.291 INFO    redirected default logger       {“from”: “stderr”, “to”: “stdout”}
 {“level”:“info”,“ts”:1758806388.29951,“logger”:“admin”,“msg”:“admin endpoint started”,“address”:“localhost:2019”,“enforce_origin”:false,“origins”:\[“//localhost:2019”,“//\[::1\]:2019”,“//127.0.0.1:2019”\]}
 2025/09/25 13:19:48.350 INFO    failed to sufficiently increase receive buffer size (was: 208 kiB, wanted: 2048 kiB, got: 416 kiB). See https://github.com/lucas-clemente/quic-go/wiki/UDP-Receive-Buffer-Size for details.
 {“level”:“info”,“ts”:1758806388.3717754,“msg”:“autosaved config (load with --resume flag)”,“file”:“/home/dionysus/.config/caddy/autosave.json”}
 {“level”:“info”,“ts”:1758806388.3719318,“msg”:“serving initial configuration”}

  • navigate to 192.168.0.X/syncthing → Secure Connection Failed

    • Error code: SSL_ERROR_INTERNAL_ERROR_ALERT

  • put config into block with LAN IP

  • browser prompts with insecure page, click continue anyway

  • blank page

  • 09:29:48:(~)$curl -v 192.168.0.30/syncthing

  * Trying 192.168.0.X:80…
  * Connected to 192.168.0.X (192.168.0.X) port 80 (#0)

  > GET /syncthing HTTP/1.1
  > Host: 192.168.0.X
  > User-Agent: curl/7.88.1
  > Accept: */*

  < HTTP/1.1 308 Permanent Redirect
  < Connection: close
  < Location: https://192.168.0.X/syncthing
  < Server: Caddy
  < Date: Thu, 25 Sep 2025 13:29:54 GMT
  < Content-Length: 0
  <

  * Closing connection 0
  • increased receive buffer size
  $ sudo sysctl -w net.core.rmem_max=7500000
  net.core.rmem_max = 7500000
  $ sudo sysctl -w net.core.wmem_max=7500000
  net.core.wmem_max = 7500000
  • 192.168.0.X/syncthing still loads blank page. No access logs.
  • caddyfile:
{
        log default {
                output stdout
                format json
                level debug
                include *
        }
}

192.168.0.X {
        handle_path /syncthing/* {
                reverse_proxy http://localhost:8384 {
                        header_up Host {upstream_hostport}
                }
        }
}

I did a bunch of trouble shooting last night, and never managed to got it working. That’s why I reset my syncthing config before posting, because I didn’t keep track of all the things I had changed. I would be very grateful if anyone could help me troubleshoot.

2

That doesn’t tell us that much. This is most likely caddys auto redirect from http to https at work here.

3

EDIT: Yay, it’s working! It seems the problem was i wasn’t putting the trailing slash when actually attempting to use the reverse-proxy. orangepizero2.local/syncthing/ works as expected!

Does this help?

{
  "level": "info",
  "ts": 1758859427.5001345,
  "logger": "http.log.access.log0",
  "msg": "handled request",
  "request": {
    "remote_ip": "192.168.0.7",
    "remote_port": "41036",
    "proto": "HTTP/2.0",
    "method": "GET",
    "host": "orangepizero2.local",
    "uri": "/syncthing",
    "headers": {
      "Accept": [
        "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"
      ],
      "Accept-Encoding": [
        "gzip, deflate, br, zstd"
      ],
      "Upgrade-Insecure-Requests": [
        "1"
      ],
      "Sec-Fetch-Dest": [
        "document"
      ],
      "Sec-Fetch-Site": [
        "cross-site"
      ],
      "Te": [
        "trailers"
      ],
      "User-Agent": [
        "Mozilla/5.0 (X11; Linux x86_64; rv:143.0) Gecko/20100101 Firefox/143.0"
      ],
      "Accept-Language": [
        "en-US,en;q=0.5"
      ],
      "Sec-Gpc": [
        "1"
      ],
      "Sec-Fetch-Mode": [
        "navigate"
      ],
      "Priority": [
        "u=0, i"
      ]
    },
    "tls": {
      "resumed": false,
      "version": 772,
      "cipher_suite": 4865,
      "proto": "h2",
      "server_name": "orangepizero2.local"
    }
  },
  "user_id": "",
  "duration": 5.3166e-05,
  "size": 0,
  "status": 0,
  "resp_headers": {
    "Alt-Svc": [
      "h3=\":443\"; ma=2592000"
    ],
    "Server": [
      "Caddy"
    ]
  }
}
1 Like