HTTP 504 — Gateway Timeout

What 504 actually means

Like a 502, this comes from an intermediary reporting on the server behind it — but here the upstream was alive and simply too slow. The proxy hit its timeout and returned an error rather than waiting forever. That distinction matters when debugging: a 502 points at a process that is down or unreachable, a 504 points at one that is running but stuck, usually on a slow query, an external API call, or a lock.

Common causes

• A slow database query, often one missing an index
• An external API call the application makes with no timeout of its own
• A request doing too much work synchronously — a large report or export
• A deadlock or lock contention holding the request open
• The upstream saturated, so requests queue behind others
• A proxy timeout set lower than the application's own worst-case response time

If you're just trying to view the page

1. Wait and retry — a slow query or a busy period often clears
2. If it happens on one heavy action, such as generating a report, try a smaller date range or fewer items
3. Check the status page; a 504 across a whole site means the operators already know
4. Nothing on your side will speed the server up

If it's your site

1. Find the slow operation before raising any timeout — a longer timeout turns a fast failure into a slow one
2. Check the database slow query log and add the missing index; this is the single most common root cause
3. Set explicit timeouts on every outbound HTTP call the application makes, so one slow dependency cannot consume a request slot indefinitely
4. Move long work to a background job and return 202 with a status URL instead of holding the connection
5. If you must raise the limit, raise `proxy_read_timeout` (Nginx) or the load balancer idle timeout — and remember the smallest timeout in the chain wins
6. Watch for cascading failures: one slow dependency can saturate the pool and turn into site-wide 504s

Reference

Status code

504

Reason phrase

Gateway Timeout

Category

5xx — Server Error

Cacheable by default

No

Defined in

RFC 9110 §15.6.5