504 Gateway Timeout

What It Means

A 504 error means your request made it to a proxy (like Nginx or a CDN), but the proxy gave up waiting for your application server to respond. The request took too long.

Common Causes

• Slow database queries — Query takes longer than the proxy timeout
• External API calls — Waiting on a third-party API that's slow or down
• CPU-intensive operations — Heavy computation blocking the response
• Network issues — Latency between proxy and app server
• Insufficient resources — Server struggling under load
• Proxy timeout too low — Timeout configured lower than typical request time

How to Debug

1. Reproduce the slow request — Which endpoints are timing out?
2. Profile the endpoint — What's taking so long?
3. Check database queries — Are there slow queries? Missing indexes?
4. Check external calls — Are third-party APIs responding slowly?
5. Check server resources — CPU, memory, I/O

Nginx Timeout Configuration

# Increase timeouts in nginx.conf or site config
location / {
    proxy_pass http://app;

    # Time to establish connection
    proxy_connect_timeout 60s;

    # Time to send request
    proxy_send_timeout 60s;

    # Time to receive response (most relevant for 504)
    proxy_read_timeout 60s;
}

Finding Slow Queries

# PostgreSQL - find slow queries
SELECT query, calls, mean_time, total_time
FROM pg_stat_statements
ORDER BY mean_time DESC
LIMIT 10;

# MySQL - enable slow query log
SET GLOBAL slow_query_log = 'ON';
SET GLOBAL long_query_time = 1;

504 vs 408

Solutions

• Optimize slow operations — Add indexes, cache results, optimize queries
• Add timeouts to external calls — Don't let slow APIs block indefinitely
• Move to background jobs — Long operations should be async
• Increase proxy timeout — If the operation genuinely needs more time
• Add caching — Reduce repeat expensive operations
• Scale up/out — More resources to handle load

How to Monitor for 504 Errors

504 errors indicate performance degradation that's about to become downtime. UptimeSignal tracks response times and alerts you when endpoints start timing out. Catch slow responses before they become full timeouts. See also: 502 Bad Gateway, 522 Connection Timed Out.

Frequently Asked Questions