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nginx: upstream sent too big header
===================================

### [\#Nginx](https://rocketeersapp.com/knowledge/nginx)

This 502 variant happens when your application sends response headers larger than the buffers nginx reserves for them. Common with big cookies, large session data, or many headers.

 Published by [Mark van Eijk](https://rocketeersapp.com/author/mark-van-eijk) on June 23, 2026 · 1 minute read

1. [About the error](#content-about-the-error)
2. [Why do I see this error](#content-why-do-i-see-this-error)
3. [Solution](#content-solution)
4. [Fix the root cause too](#content-fix-the-root-cause-too)

[\#](#content-about-the-error "Permalink")About the error
---------------------------------------------------------

The visitor gets a [502 Bad Gateway](/502-bad-gateway-nginx) and the nginx error log explains why:

 ```
upstream sent too big header while reading response header from upstream

```

nginx reserves a fixed-size buffer for the response headers it reads back from your application (PHP-FPM or a proxied service). If the headers don't fit, nginx can't process the response and returns a 502.

[\#](#content-why-do-i-see-this-error "Permalink")Why do I see this error
-------------------------------------------------------------------------

- **Large cookies**, especially a big session cookie or many cookies set at once.
- A long `Set-Cookie` from a fat session payload.
- Many or unusually large custom headers.
- A redirect with a very long `Location` URL.

It frequently appears right after login, when the session and its cookie grow.

[\#](#content-solution "Permalink")Solution
-------------------------------------------

Increase the FastCGI buffer sizes so the headers fit. For a PHP-FPM app:

 ```
fastcgi_buffer_size 32k;
fastcgi_buffers 8 16k;
fastcgi_busy_buffers_size 64k;

```

For a proxied application (`proxy_pass`), the equivalents are:

 ```
proxy_buffer_size 32k;
proxy_buffers 8 16k;
proxy_busy_buffers_size 64k;

```

Put these in the relevant `location` or `server` block, then validate and reload:

 ```
nginx -t && systemctl reload nginx

```

### [\#](#content-fix-the-root-cause-too "Permalink")Fix the root cause too

Bigger buffers treat the symptom. If the headers are huge because you're storing a lot in the session (and therefore the cookie), trim it. In Laravel, keep large data server-side by using a non-cookie session driver such as `redis` or `database` rather than the `cookie` driver, so only a small session id travels in the header:

 ```
SESSION_DRIVER=redis

```

See [Redis connection refused in Laravel](/redis-connection-refused-laravel) if you switch to the Redis driver.

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