502 bad gateway - upstream sent too big header while reading response header from upstream

[Eric Falcao]

Hi Everyone, this issue has been hurting me pretty badly so I'm hoping
someone else has seen and fixed this:

I have a rails request which generates a long redirect url, over 1k
chars unfortunately, here is how things proceed

- user can use the entire site fine
- users posts to the action with the long redirect
- rails app processes and send back the redirect
- i see "upstream sent too big header while reading response header
from upstream" in the nginx log
- 502 bad gateway in the web browser

After searching, I have tried various permutations of:

fastcgi_buffers, fastcgi_buffer_size, proxy_buffers, proxy_buffer_size
and none have worked.

Any advice?

[Hongli Lai]

It's got nothing to do with buffer sizes. Nginx simply refuses to
accept response headers that are larger than a certain limit for
security reasons. You should check which headers your web app are
exactly sending and verify whether that's normal.

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