ETIMEDOUT — Connection Timed Out Debugging

ETIMEDOUT (errno 110)

ETIMEDOUT indicates that a connection attempt or I/O operation did not complete within the allowed time. Unlike ECONNREFUSED (which gets an immediate rejection), a timeout means no response was received at all.

Why Timeouts Happen

1. Firewall silently dropping packets — The most common cause. The target host's firewall drops incoming packets without sending a RST or ICMP response
2. DNS resolution failure — The hostname cannot be resolved, and the DNS query itself times out
3. Network routing issues — Packets cannot reach the destination due to misconfigured routes
4. Server overloaded — The server's accept queue is full and it cannot process new connections
5. MTU/fragmentation issues — Large packets being dropped by intermediate network devices

Connection Timeout vs Read Timeout

• Connection timeout — Time allowed for the TCP three-way handshake to complete
• Read timeout (also called socket timeout) — Time allowed to receive data after the connection is established

// Node.js: separate timeouts
const controller = new AbortController();
const timeout = setTimeout(() => controller.abort(), 5000);

fetch('https://api.example.com/data', {
  signal: controller.signal
}).finally(() => clearTimeout(timeout));

Troubleshooting Steps

1. Verify DNS: nslookup hostname or dig hostname
2. Check reachability: ping hostname (ICMP may be blocked)
3. Test TCP connection: nc -zv hostname port -w 5
4. Trace the route: traceroute hostname or mtr hostname
5. Check from different network: VPN, different server, or mobile hotspot
6. Review firewall rules: Both local and remote

Setting Appropriate Timeouts

• Health checks: 2-5 seconds
• Internal API calls: 5-10 seconds
• External API calls: 10-30 seconds
• Batch processing: 60-300 seconds