HTTP downloads randomly get stuck until client timeout

Richard Stanway r1ch+nginx at
Tue Jan 31 15:19:59 UTC 2017

Hi all,
I'm experiencing odd behavior with some larger HTTP file downloads from my
site. The files will download for a seemingly random amount of bytes then
the connection freezes until "send_timeout" expires, at which point the
error log shows "client timed out (110: Connection timed out) while sending
response to client".

A tcpdump shows both ends successfully passing packets with no packet loss.
nginx is pretty stock from the repository, no 3rd party modules
or complex options, mostly static files and fastcgi / PHP. The behavior is
very intermittent, but happens regardless of client browser / IP /
requested file.

I was able to captured a debug log when this happened, it is available at (some rewrite details and variables have
been omitted)

# nginx -V
nginx version: nginx/1.10.2
built by gcc 4.9.2 (Debian 4.9.2-10)
built with OpenSSL 1.0.1t  3 May 2016
TLS SNI support enabled
configure arguments: --prefix=/etc/nginx --sbin-path=/usr/sbin/nginx
--modules-path=/usr/lib/nginx/modules --conf-path=/etc/nginx/nginx.conf
--http-log-path=/var/log/nginx/access.log --pid-path=/var/run/
--http-scgi-temp-path=/var/cache/nginx/scgi_temp --user=nginx --group=nginx
--with-file-aio --with-threads --with-ipv6 --with-http_addition_module
--with-http_auth_request_module --with-http_dav_module
--with-http_flv_module --with-http_gunzip_module
--with-http_gzip_static_module --with-http_mp4_module
--with-http_random_index_module --with-http_realip_module
--with-http_secure_link_module --with-http_slice_module
--with-http_ssl_module --with-http_stub_status_module
--with-http_sub_module --with-http_v2_module --with-mail
--with-mail_ssl_module --with-stream --with-stream_ssl_module
--with-cc-opt='-g -O2 -fstack-protector-strong -Wformat
-Werror=format-security -Wp,-D_FORTIFY_SOURCE=2'
--with-ld-opt='-Wl,-z,relro -Wl,-z,now -Wl,--as-needed'

sendfile, tcp_nopush, tcp_nodelay are enabled.
accept_mutex, aio is disabled.

Linux karak 3.16.0-4-amd64 #1 SMP Debian 3.16.36-1+deb8u2 (2016-10-19)
x86_64 GNU/Linux

I've also tried mainline nginx/1.11.9 from the repository and the
problem persisted. Any advice on what I should be looking at to resolve
this would be very welcome!


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