louislam/uptime-kuma · error · Error

No Resolver Servers specified. Please specify at least one r

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.

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 : []),

View on GitHub (pinned to 6b5ea01557)

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" }

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

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

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

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

• Packet size must be between ${PING_PACKET_SIZE_MIN} and ${PI
• None of the configured resolver servers could be resolved to
• Service Name is required.
• Invalid service name. Please use the internal Service Name (
• Invalid PM2 process name.

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