Strange repeated errors

[Greg]

Hi,

I've a tail -f error.log running, and saw some strange errors, repeated 
each minutes at same second (26), from same host and same URL :

2012/05/22 15:13:26 [error] 12410#0: *4714521 upstream timed out (110: 
Connection timed out) while reading response header from upstream, 
client: 177.65.240.189, server: www.mydomain1.com, request: "GET 
/?track=lang-BR&uid=159669961 HTTP/1.1", upstream: 
"http://10.0.0.26:80/?track=lang-BR&uid=159669961", host: 
"sub.mydomain1.com"
2012/05/22 15:14:26 [error] 12410#0: *4714521 upstream timed out (110: 
Connection timed out) while reading response header from upstream, 
client: 177.65.240.189, server: www.mydomain1.com, request: "GET 
/?track=lang-BR&uid=159669961 HTTP/1.1", upstream: 
"http://10.0.1.26:80/?track=lang-BR&uid=159669961", host: 
"sub.mydomain1.com"
2012/05/22 15:15:26 [error] 12410#0: *4714521 upstream timed out (110: 
Connection timed out) while reading response header from upstream, 
client: 177.65.240.189, server: www.mydomain1.com, request: "GET 
/?track=lang-BR&uid=159669961 HTTP/1.1", upstream: 
"http://10.0.0.31:80/?track=lang-BR&uid=159669961", host: 
"sub.mydomain1.com"
2012/05/22 15:16:26 [error] 12410#0: *4714521 upstream timed out (110: 
Connection timed out) while reading response header from upstream, 
client: 177.65.240.189, server: www.mydomain1.com, request: "GET 
/?track=lang-BR&uid=159669961 HTTP/1.1", upstream: 
"http://10.0.1.31:80/?track=lang-BR&uid=159669961", host: 
"sub.mydomain1.com"
2012/05/22 15:17:26 [error] 12410#0: *4714521 upstream timed out (110: 
Connection timed out) while reading response header from upstream, 
client: 177.65.240.189, server: www.mydomain1.com, request: "GET 
/?track=lang-BR&uid=159669961 HTTP/1.1", upstream: 
"http://10.0.0.32:80/?track=lang-BR&uid=159669961", host: 
"sub.mydomain1.com"
2012/05/22 15:18:26 [error] 12410#0: *4714521 upstream timed out (110: 
Connection timed out) while reading response header from upstream, 
client: 177.65.240.189, server: www.mydomain1.com, request: "GET 
/?track=lang-BR&uid=159669961 HTTP/1.1", upstream: 
"http://10.0.1.32:80/?track=lang-BR&uid=159669961", host: 
"sub.mydomain1.com"
2012/05/22 15:19:26 [error] 12410#0: *4714521 upstream timed out (110: 
Connection timed out) while reading response header from upstream, 
client: 177.65.240.189, server: www.mydomain1.com, request: "GET 
/?track=lang-BR&uid=159669961 HTTP/1.1", upstream: 
"http://10.0.0.33:80/?track=lang-BR&uid=159669961", host: 
"sub.mydomain1.com"
2012/05/22 15:20:26 [error] 12410#0: *4714521 upstream timed out (110: 
Connection timed out) while reading response header from upstream, 
client: 177.65.240.189, server: www.mydomain1.com, request: "GET 
/?track=lang-BR&uid=159669961 HTTP/1.1", upstream: 
"http://10.0.1.33:80/?track=lang-BR&uid=159669961", host: 
"sub.mydomain1.com"
2012/05/22 15:21:27 [error] 12410#0: *4714521 upstream timed out (110: 
Connection timed out) while reading response header from upstream, 
client: 177.65.240.189, server: www.mydomain1.com, request: "GET 
/?track=lang-BR&uid=159669961 HTTP/1.1", upstream: 
"http://10.0.0.34:80/?track=lang-BR&uid=159669961", host: 
"sub.mydomain1.com"
2012/05/22 15:22:27 [error] 12410#0: *4714521 upstream timed out (110: 
Connection timed out) while reading response header from upstream, 
client: 177.65.240.189, server: www.mydomain1.com, request: "GET 
/?track=lang-BR&uid=159669961 HTTP/1.1", upstream: 
"http://10.0.1.34:80/?track=lang-BR&uid=159669961", host: 
"sub.mydomain1.com"
2012/05/22 15:23:27 [error] 12410#0: *4714521 upstream timed out (110: 
Connection timed out) while reading response header from upstream, 
client: 177.65.240.189, server: www.mydomain1.com, request: "GET 
/?track=lang-BR&uid=159669961 HTTP/1.1", upstream: 
"http://10.0.0.28:80/?track=lang-BR&uid=159669961", host: 
"sub.mydomain1.com"
2012/05/22 15:24:27 [error] 12410#0: *4714521 upstream timed out (110: 
Connection timed out) while reading response header from upstream, 
client: 177.65.240.189, server: www.mydomain1.com, request: "GET 
/?track=lang-BR&uid=159669961 HTTP/1.1", upstream: 
"http://10.0.1.28:80/?track=lang-BR&uid=159669961", host: 
"sub.mydomain1.com"
2012/05/22 15:25:27 [error] 12410#0: *4714521 upstream timed out (110: 
Connection timed out) while reading response header from upstream, 
client: 177.65.240.189, server: www.mydomain1.com, request: "GET 
/?track=lang-BR&uid=159669961 HTTP/1.1", upstream: 
"http://10.0.0.25:80/?track=lang-BR&uid=159669961", host: 
"sub.mydomain1.com"
2012/05/22 15:26:27 [error] 12410#0: *4714521 upstream timed out (110: 
Connection timed out) while reading response header from upstream, 
client: 177.65.240.189, server: www.mydomain1.com, request: "GET 
/?track=lang-BR&uid=159669961 HTTP/1.1", upstream: 
"http://10.0.1.25:80/?track=lang-BR&uid=159669961", host: 
"sub.mydomain1.com"

I've curl this URL, then ab (ApacheBench) it, and wasn't able to 
reproduce this error. Did you have an idea how to debug that ?

-- 
Greg
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