caddyserver/caddy · error

invalid downstream address %s: %v

Error message

invalid downstream address %s: %v

What it means

The --from (downstream/listener) address of 'caddy reverse-proxy' failed httpcaddyfile.ParseAddress. This is the address Caddy serves on, and it must be a plain host/port/scheme combination; the '%v' carries the parse detail.

Source

Thrown at modules/caddyhttp/reverseproxy/command.go:112

	internalCerts := fs.Bool("internal-certs")
	accessLog := fs.Bool("access-log")
	debug := fs.Bool("debug")

	httpPort := strconv.Itoa(caddyhttp.DefaultHTTPPort)
	httpsPort := strconv.Itoa(caddyhttp.DefaultHTTPSPort)

	to, err := fs.GetStringSlice("to")
	if err != nil {
		return caddy.ExitCodeFailedStartup, fmt.Errorf("invalid to flag: %v", err)
	}
	if len(to) == 0 {
		return caddy.ExitCodeFailedStartup, fmt.Errorf("--to is required")
	}

	// set up the downstream address; assume missing information from given parts
	fromAddr, err := httpcaddyfile.ParseAddress(from)
	if err != nil {
		return caddy.ExitCodeFailedStartup, fmt.Errorf("invalid downstream address %s: %v", from, err)
	}
	if fromAddr.Path != "" {
		return caddy.ExitCodeFailedStartup, fmt.Errorf("paths are not allowed: %s", from)
	}
	if fromAddr.Scheme == "" {
		if fromAddr.Port == httpPort || fromAddr.Host == "" {
			fromAddr.Scheme = "http"
		} else {
			fromAddr.Scheme = "https"
		}
	}
	if fromAddr.Port == "" {
		switch fromAddr.Scheme {
		case "http":
			fromAddr.Port = httpPort
		case "https":
			fromAddr.Port = httpsPort
		}

View on GitHub (pinned to 50e54ee279)

Solutions

1. Use a simple value: domain, :port, or scheme://host:port, properly quoted.
2. Fix the specific syntax error named by the wrapped message.
3. Prefer 'caddy reverse-proxy --from localhost:8080' style during testing to minimize parse surface.

Example fix

# before
caddy reverse-proxy --from 'exam ple.com:443' --to localhost:8080

# after
caddy reverse-proxy --from 'example.com:443' --to localhost:8080

if _, err := httpcaddyfile.ParseAddress(from); err != nil {
    return fmt.Errorf("--from %q is not a valid site address: %v", from, err)
}

When it happens

Trigger: 'caddy reverse-proxy --from "ht!p://bad" ...' or addresses with invalid characters, bad brackets, or malformed port.

Common situations: Typos in the scheme, stray URL components, or unquoted shell metacharacters in --from.

Related errors

• paths are not allowed: %s
• invalid to flag: %v
• --to is required
• invalid upstream address %s: %v
• invalid header flag: %v

AI-assisted analysis of caddyserver/caddy@50e54ee279 (2026-08-15). Data as JSON: /api/errors/851e1a69936b4ca4. Report an issue: GitHub.