# 504 Gateway Timeout: when the backend is too slow

> 504 Gateway Timeout means a proxy or gateway gave up waiting for a response from the upstream server behind it.

URL: https://yes-seo.com/http-status-codes/504

**504 Gateway Timeout** means a proxy, load balancer or CDN waited for the application behind it and gave up before an answer arrived. Unlike [502](https://yes-seo.com/http-status-codes/502), the backend didn’t send a broken response; it was simply too slow.

## Definition

[RFC 9110, section 15.6.5](https://www.rfc-editor.org/rfc/rfc9110#section-15.6.5): the server, “while acting as a gateway or proxy, did not receive a timely response from an upstream server it needed to access in order to complete the request.” The timeout belongs to the gateway. Nginx waits 60 seconds by default (`proxy_read_timeout`, `fastcgi_read_timeout`), and cloud load balancers have their own idle timeouts. Cloudflare reports the same situation as [524](https://yes-seo.com/http-status-codes/524).

## Common causes

- Slow database queries: missing indexes, huge joins, locked tables.

- Pages that call external APIs while rendering, and wait when those APIs are slow.

- Long-running jobs started by a web request: exports, imports, image processing, sitemaps generated on the fly.

- Too few workers for the traffic, so requests queue until they time out.

- Network problems between the proxy and the app server.

## SEO impact

Google groups 504 with other server errors ([Google’s documentation](https://developers.google.com/search/docs/crawling-indexing/http-network-errors)): Googlebot slows its crawling, indexed URLs survive brief problems, and URLs that keep failing are removed. Slowness hurts even before requests time out. Google’s [crawl budget](https://yes-seo.com/glossary/crawl-budget) guidance explains that crawl capacity goes down when a site responds slowly or returns errors. Long response times also mean a poor [time to first byte](https://yes-seo.com/glossary/ttfb) for visitors.

## How to fix a 504

### Find the slow part

```
# which requests time out?
grep "upstream timed out" /var/log/nginx/error.log | tail

# MySQL: log queries slower than 2 seconds
SET GLOBAL slow_query_log = 'ON';
SET GLOBAL long_query_time = 2;
```

### Make it faster

- Add database indexes and cache expensive queries (object cache, page cache).

- Move heavy work to a background queue and let the page poll for the result, the [202 Accepted](https://yes-seo.com/http-status-codes/202) pattern.

- Pre-generate large files such as XML sitemaps instead of building them on every request.

- Set short timeouts on outgoing API calls and fall back to cached data when they fail.

### Raise timeouts only as a stopgap

```
# Nginx
proxy_read_timeout 120s;      # for proxy_pass
fastcgi_read_timeout 120s;    # for PHP-FPM

; PHP-FPM pool and php.ini must allow it too
request_terminate_timeout = 120s
max_execution_time = 120
```

Timeouts need to line up across layers; otherwise the shortest one still wins.

## How to check

The [HTTP status checker](https://yes-seo.com/http-status-checker) shows each URL’s status and response time, so you can spot slow pages before they hit the limit, and the [page speed test](https://yes-seo.com/page-speed-test) breaks down server response time for a single page.

```
HTTP/1.1 504 Gateway Time-out
Server: nginx
Content-Type: text/html
Content-Length: 160
```

Nginx still prints the old “Gateway Time-out” spelling; it’s the same status.

## Frequently asked questions

### What is the difference between 504 and 502?

A 504 means the upstream server didn’t answer in time. A 502 means it answered with something invalid or dropped the connection. Both come from a proxy or gateway, not the application itself.

### Can I fix a 504 by increasing timeouts?

Only temporarily. Longer timeouts hide the slowness from the gateway, but visitors and crawlers still wait. Speed up the slow request or move the work to a background job.

### Does a 504 Gateway Timeout affect SEO?

Yes. Google treats it as a server error and crawls less, and URLs that keep timing out can be removed from the index. Slow responses also reduce how much Google crawls in general.