As per the docs <http://nginx.org/en/docs/http/ngx_http_upstream_module.html#var_upstream_status>, it is said this variable contains all the status codes returned by each upstream interrogated. >From what I understood, server1 returned 504, server2 returned 502.
Those statuses are included in what the proxy_next_upstream <http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_next_upstream> directive describes as an 'unsuccessful attempt', thus it seems every server of your upstream group has been tried (default number of attempts is 1 as per the server <http://nginx.org/en/docs/http/ngx_http_upstream_module.html#server> directive). nginx then returned the result of the last attempt, resulting in a 502 answer passed back to the client. I do not know what a 'special response' is. Custom header? I also do not get why you are surprised by the fact 5xx responses end up with them being shown to client. They are perfectly valid HTTP status codes, indicating a server error, and are shown because no upstream server returned a 'successful' status code. --- *B. R.* On Fri, Aug 19, 2016 at 9:54 PM, Frank Liu <[email protected]> wrote: > Hi, > > I am using nginx as proxy with two upstream servers. In the access log, I > log the upstream_address, upstream_status, status (downstream), a special > response header from upstream, etc. > > A few times I see in the log upstream_address: server1:port, server2:port > with upstream_status: 504, 502 status: 502 special header: - > Since there is the special response header, I assume nginx didn't get any > responses from either upstream servers. Why would upstream_status shows 504 > and 502? Those code must not come from upstream, is it generated by nginx > self? I thought it would be -, - since there are no upstream_status > returned from upstream. > > Thanks! > Frank > > > _______________________________________________ > nginx mailing list > [email protected] > http://mailman.nginx.org/mailman/listinfo/nginx >
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