This is a question about the "$status" log value when "proxy_read_timeout" occurs.

[Maxim Dounin]

Hello!

On Tue, Jan 16, 2024 at 01:15:09PM +0900, 박규철 wrote:

> This is a question about the "$status" log value when "proxy_read_timeout"
> occurs.
> Nginx version in use: v1.25.3
> 
> Contents of 1Mbyte size were requested to [Origin Server].
> A response up to approximately 500Kbytes in size, including the header, was
> received without delay.
> However, after 500Kbytes, no response was received from Origin for 3
> seconds and the connection (time-out)
> Since the message "upstream timed out...while reading upstream" was logged
> in the error log, I think the connection was lost due to the
> "proxy_read_timeout 3s" setting.
> 
> While checking the log, I noticed that the "$status" value in the access
> log was different from what I thought.
> In my opinion, if the connection was terminated by "proxy_read_timeout",
> the "$status" value would be 5xx, but the "$status" value in the saved
> access log was 200.
> 
> A normal response was not completed due to "proxy_read_timeout", so I would
> like to know why the "$status" value is stored as 200 instead of 5xx.
> Should I check a variable other than "$status" for responses to abnormal
> timeouts such as "proxy_read_timeout"?

The $status variable shows the status as sent to the client in the 
response headers.  When proxy_read_timeout happens, the response 
headers are already sent, so $status contains 200 as sent to the 
client.

For errors happened during sending the response body, consider 
looking into the error log.  Some generic information about 
successful request completion might be found in the 
$request_completion variable 
(http://nginx.org/r/$request_completion).  Note though that it 
might not be set for variety of reasons.

-- 
Maxim Dounin
http://mdounin.ru/