fatedier/frp · error

custom domain [%s] should not belong to subdomain host [%s]

Error message

custom domain [%s] should not belong to subdomain host [%s]

What it means

Error "custom domain [%s] should not belong to subdomain host [%s]" thrown in fatedier/frp.

Source

Thrown at pkg/config/v1/validation/proxy.go:87

		return err
	}
	return nil
}

func validateDomainConfigForClient(c *v1.DomainConfig) error {
	if c.SubDomain == "" && len(c.CustomDomains) == 0 {
		return errors.New("subdomain and custom domains should not be both empty")
	}
	return nil
}

func validateDomainConfigForServer(c *v1.DomainConfig, s *v1.ServerConfig) error {
	subDomainHost := strings.ToLower(s.SubDomainHost)
	for _, domain := range c.CustomDomains {
		canonicalDomain := strings.ToLower(domain)
		if subDomainHost != "" && len(strings.Split(subDomainHost, ".")) < len(strings.Split(canonicalDomain, ".")) {
			if strings.HasSuffix(canonicalDomain, "."+subDomainHost) {
				return fmt.Errorf("custom domain [%s] should not belong to subdomain host [%s]", domain, s.SubDomainHost)
			}
		}
	}

	if c.SubDomain != "" {
		if s.SubDomainHost == "" {
			return errors.New("subdomain is not supported because this feature is not enabled in server")
		}

		if strings.Contains(c.SubDomain, ".") || strings.Contains(c.SubDomain, "*") {
			return errors.New("'.' and '*' are not supported in subdomain")
		}
	}
	return nil
}

func ValidateProxyConfigurerForClient(c v1.ProxyConfigurer) error {
	base := c.GetBaseConfig()

View on GitHub (pinned to 6c8a8d0a97)

Solutions

1. Remove the custom domain that ends with the server subDomainHost, or use subdomain instead of customDomains for that name.
2. Ask the server administrator for the configured subDomainHost and select a custom domain outside of it.

When it happens

Trigger: Raised by validateDomainConfigForClient in pkg/config/v1/validation/proxy.go when a customDomain entry falls inside the subdomainHost domain, which would conflict with generated subdomains.

Common situations: customDomains contains a name under the subdomainHost domain (e.g. subdomainHost is example.com and customDomains includes foo.example.com). Fix by removing the overlapping custom domain or choosing a different subdomainHost.

AI-assisted analysis of fatedier/frp@6c8a8d0a97 (2026-08-15). Data as JSON: /api/errors/683e1fa9bf7e5791. Report an issue: GitHub.