louislam/uptime-kuma · error · Error

No Resolver Servers specified. Please specify at least one…

Error message

No Resolver Servers specified. Please specify at least one resolver server like 1.1.1.1 or a hostname

What it means

Thrown by DnsMonitorType.resolveDnsResolverServers(dnsResolveServer) when the input, after removing all whitespace and splitting on commas, yields zero non-empty entries. The DNS monitor needs at least one resolver to build the Resolver it queries against.

Solutions

  1. Set dnsResolveServer to at least one IP (e.g. "1.1.1.1") or resolvable hostname, comma-separated for multiple.
  2. Provide a default in your config layer when the field is blank: value || "1.1.1.1".
  3. Trim and validate the field length in the UI/API before reaching the monitor runtime.

Example fix

// before
{ type: "dns", dnsResolveServer: "" }
// after
{ type: "dns", dnsResolveServer: "1.1.1.1,8.8.8.8" }
Defensive patterns

Strategy: validation

Validate before calling

function hasResolver(s) {
  return typeof s === "string" && s.replace(/\s/g, "").split(",").filter(x => x !== "").length > 0;
}

Type guard

function isNonEmptyResolverList(s) {
  return typeof s === "string" && s.replace(/\s/g, "").split(",").filter(Boolean).length > 0;
}

Try / catch

try {
  await dnsMonitor.monitor(...);
} catch (e) {
  if (/No Resolver Servers specified/.test(e.message)) return badRequest("dnsResolveServer is required");
  throw e;
}

Prevention

When it happens

Trigger: Save or run a DNS monitor whose dnsResolveServer field is "", " ", ",,,", or only commas/spaces. The regex /\s/g strips all whitespace before splitting.

Common situations: User clears the resolver field expecting a default; default is not applied here. Field accidentally set to a comma separator only. Migration that null-coalesced to empty string.

Related errors

AI-assisted analysis of louislam/uptime-kuma@6b5ea01557 (2026-08-12). Data as JSON: /api/errors/642d3b413231020a. Report an issue: GitHub.

Appendix: source

Thrown at server/monitor-types/dns.js:124

     * We are primarily doing this to support hostnames of docker containers like adguard.
     *
     * - Whitespace is removed from the input string
     * - Empty entries are ignored
     * - IP literals (IPv4 / IPv6) are accepted as-is
     * - Hostnames are resolved to both A and AAAA records in parallel
     * - Invalid or unresolvable entries are logged and skipped
     * @param {string} dnsResolveServer - Comma-separated list of resolver servers (IPs or hostnames)
     * @returns {Promise<Array<string>>} Array of resolved IP addresses
     * @throws {Error} If no valid resolver servers could be parsed or resolved
     */
    async resolveDnsResolverServers(dnsResolveServer) {
        // Remove all spaces, split into array, remove all elements that are empty
        const addresses = dnsResolveServer
            .replace(/\s/g, "")
            .split(",")
            .filter((x) => x !== "");
        if (!addresses.length) {
            throw new Error(
                "No Resolver Servers specified. Please specify at least one resolver server like 1.1.1.1 or a hostname"
            );
        }
        const resolver = new Resolver();

        // Make promises to be resolved concurrently
        const promises = addresses.map(async (e) => {
            if (net.isIP(e)) {
                // If IPv4 or IPv6 addr, immediately return
                return [e];
            }

            // Otherwise, attempt to resolve hostname
            const [v4, v6] = await Promise.allSettled([resolver.resolve4(e), resolver.resolve6(e)]);

            const addrs = [
                ...(v4.status === "fulfilled" ? v4.value : []),
                ...(v6.status === "fulfilled" ? v6.value : []),

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