Proxy_buffering off causes truncated responses when backend emits response in small chunks

We use nginx as both a load-balancer and webserver. This issue is with
nginx functioning as a load-balancer.

We reverse proxy to 6 nginx webservers running a number of Unicorn
application servers, these webserver nginx instances also run Evan
mod_zip to assemble archives on the fly. We have discovered under
circumstances the load-balancing nginx will “hang-up” on the webserver
the load-balancer is configured with proxy_buffering off, however
proxy_buffering on seems to succeed. We would prefer to run without
proxy_buffering to prevent the load-balancer’s local storage from being

Our default setup uses nginx 0.7.65 for both the load-balancer and the
webserver, however switching to using 1.0.12 as the load-balancer has
same problem. We have experimented with different software doing the
load-balancing and it does not exhibit this issue.

I’ve have linked the nginx configuration file we’re using on the load
balancer, and debug logs for both 0.7.65 and 1.0.12.

The buffering on log is very long, but it does show success of a 4.8GB
response, the other responses always fail at the same point (826 MB).

The client sees the following (in access.log):

$ curl -b cookie.txt -o
% Total % Received % Xferd Average Speed Time Time Time
Dload Upload Total Spent Left
16 4922M 16 826M 0 0 1906k 0 0:44:03 0:07:23 0:36:40
curl: (18) transfer closed with 4294967296 bytes remaining to read

The nginx instance serving as the webserver logs:
Feb 07 15:03:39 ip-10-2-185-35 error.log: 2012/02/07 23:03:39 [info]
21425#0: *16656299 client closed prematurely connection, so upstream
connection is closed too (104: Connection reset by peer) while reading
upstream, client:, server:, request: “GET
/folders/7816672/archive HTTP/1.0”, subrequest: “/s3/asset-27235062”,
upstream: "",
host: “


On Tue, Feb 07, 2012 at 03:54:08PM -0800, W. Andrew Loe III wrote:

If you want to disable disk buffering you don’t need to disable
buffering at all. Use

proxy_max_temp_file_size 0;


The only valid reason to disable buffering completely with
“proxy_buffering off” is when you need even single byte from
backend to be immediately passed to client, i.e. as in some
streaming / long polling cases.

The buffering on log is very long, but it does show success of a 4.8GB
curl: (18) transfer closed with 4294967296 bytes remaining to read

The response is over 4G, and this won’t work with “proxy_buffering
off” in 1.0.x on 32bit systems. The non-buffered mode was
originally designed for small memcached responses and used to use
size_t for length storage.

You have to upgrade to 1.1.x where it now uses off_t and will be
able to handle large responses even on 32bit platforms.
Alternatively, just forget about “proxy_buffering off” as you
don’t need it anyway, see above.

Maxim D.

Mystery solved. I will just proxy_max_temp_file_size 0, as the intention
was to just avoid the disk.

Thank you!