FlowiseAI/Flowise · error · Error

DNS resolution failed for ${hostname}

Error message

DNS resolution failed for ${hostname}

What it means

Thrown by resolveAndValidate() when dns.lookup() returns an empty records array for the hostname. Normally dns.lookup throws ENOTFOUND for unresolvable hostnames, so reaching this branch (records.length === 0) is itself unusual — it indicates the OS resolver returned no A/AAAA records without throwing. The error surfaces a hostname that cannot be mapped to any IP for deny-list validation.

Source

Thrown at packages/components/src/httpSecurity.ts:318

    // Strip IPv6 brackets if present
    if (hostname.startsWith('[') && hostname.endsWith(']')) {
        hostname = hostname.slice(1, -1)
    }
    const protocol: 'http' | 'https' = u.protocol === 'https:' ? 'https' : 'http'

    if (ipaddr.isValid(hostname)) {
        isDeniedIP(hostname, denyList)
        return {
            hostname,
            ip: hostname,
            family: hostname.includes(':') ? 6 : 4,
            protocol
        }
    }

    const records = await dns.lookup(hostname, { all: true })
    if (records.length === 0) {
        throw new Error(`DNS resolution failed for ${hostname}`)
    }

    for (const r of records) {
        isDeniedIP(r.address, denyList)
    }

    const chosen = records.find((r) => r.family === 4) ?? records[0]

    return {
        hostname,
        ip: chosen.address,
        family: chosen.family as 4 | 6,
        protocol
    }
}

function createPinnedAgent(target: ResolvedTarget, options?: { ca?: string | string[] | Buffer }): http.Agent | https.Agent {
    const Agent = target.protocol === 'https' ? https.Agent : http.Agent

View on GitHub (pinned to abe4a8601a)

Solutions

1. Verify the hostname resolves from the runtime environment: run dig or nslookup in the same container/host.
2. Retry the request after confirming DNS is healthy (transient failures do occur).
3. If the hostname is internal, ensure the runtime can reach the corporate/internal DNS resolver.
4. Fall back to a cached IP if the hostname is known-stable and the failure is transient.

Example fix

// before
const resp = await secureFetch('https://flakey-host.example.com/path')

// after
// pre-check resolution and retry once on failure
async function safeFetch(url) {
  try { return await secureFetch(url) }
  catch (e) {
    if (String(e).includes('DNS resolution failed')) {
      await new Promise(r => setTimeout(r, 500))
      return secureFetch(url)
    }
    throw e
  }
}

// Pre-resolve to fail fast with a clear message
import dns from 'dns/promises'

async function ensureResolvable(hostname: string) {
  const records = await dns.lookup(hostname, { all: true })
  if (!records.length) throw new Error(`No DNS records for ${hostname}`)
  return records
}

await ensureResolvable(new URL(url).hostname)
await secureFetch(url)

async function fetchWithDnsRetry(url: string, init?: any, retries = 2) {
  for (let attempt = 0; attempt <= retries; attempt++) {
    try {
      return await secureFetch(url, init)
    } catch (e) {
      if (String(e).includes('DNS resolution failed') && attempt < retries) {
        await new Promise((r) => setTimeout(r, 500 * (attempt + 1)))
        continue
      }
      throw e
    }
  }
  throw new Error('unreachable')
}

When it happens

Trigger: A URL whose hostname passes the ipaddr.isValid() check (i.e. it is a hostname, not a literal IP) but for which dns.lookup returns zero records. Possible with exotic resolver configurations, transient DNS issues, or hostnames that exist in /etc/hosts with no resolved address. The check at line 317 fires after the await.

Common situations: Misconfigured DNS or a hostname typo. A hostname that resolves intermittently. A private DNS zone unreachable from the runtime. /etc/hosts entry with no address. Network partition during resolution. A hostname that only has records of a family not queried.

Understand the failure class

• DNS resolution errors: ENOTFOUND and getaddrinfo failures — how hostname lookups fail and how to debug them.

Related errors

• Access to this host is denied by policy.
• Failed to post ${url}: ${error}
• Failed to make GET request: ${error instanceof Error ? error
• Failed to make POST request: ${error instanceof Error ? erro
• Failed to make PUT request: ${error instanceof Error ? error

AI-assisted analysis of FlowiseAI/Flowise@abe4a8601a (2026-08-12). Data as JSON: /api/errors/f787443166c3d6b1. Report an issue: GitHub.