How to fix Error: FORMERR (invalid query format) in Node.js

const dns = require('dns');

// Check your hostname
const hostname = 'example.com'; // Replace with your actual hostname

// Validate basic format
if (!/^[a-zA-Z0-9.-]+$/.test(hostname)) {
  console.log('Invalid hostname format:', hostname);
}

dns.lookup(hostname, (err, address) => {
  if (err) {
    console.error('DNS error:', err.code, err.message);
  } else {
    console.log('Resolved to:', address);
  }
});

const dns = require('dns');

// Set custom DNS servers
dns.setServers(['8.8.8.8', '1.1.1.1']);

dns.resolve4('example.com', (err, addresses) => {
  if (err) {
    console.error('Still failing with public DNS:', err.code);
  } else {
    console.log('Success with public DNS:', addresses);
  }
});

// If using a library like 'dns-packet' or similar
const packet = require('dns-packet');

const query = packet.encode({
  type: 'query',
  id: 1,
  flags: packet.RECURSION_DESIRED,
  questions: [{
    type: 'A',
    name: 'example.com'
  }]
  // Do NOT include edns_options or additional sections that might trigger FORMERR
});

const dns = require('dns').promises;

async function resolveWithRetry(hostname, maxAttempts = 3) {
  for (let attempt = 1; attempt <= maxAttempts; attempt++) {
    try {
      const addresses = await dns.resolve4(hostname);
      return addresses;
    } catch (err) {
      console.log(`Attempt ${attempt} failed:`, err.code);

      if (err.code === 'FORMERR') {
        // Try alternate resolution method
        try {
          const result = await dns.lookup(hostname);
          return [result.address];
        } catch (lookupErr) {
          if (attempt === maxAttempts) throw lookupErr;
        }
      }

      if (attempt === maxAttempts) throw err;

      // Wait before retry
      await new Promise(resolve => setTimeout(resolve, 1000 * attempt));
    }
  }
}

resolveWithRetry('example.com')
  .then(addresses => console.log('Resolved:', addresses))
  .catch(err => console.error('All attempts failed:', err));

# View current DNS servers
cat /etc/resolv.conf

# Should see entries like:
# nameserver 8.8.8.8
# nameserver 8.8.4.4

# Check systemd-resolved status
systemctl status systemd-resolved

# View resolved DNS servers
resolvectl status

# Run container with custom DNS
docker run --dns 8.8.8.8 --dns 8.8.4.4 your-image

# Or in docker-compose.yml:
# dns:
#   - 8.8.8.8
#   - 8.8.4.4