Split documentation

docs/user-guide/log-format.md

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+# Log format
+
+The default configuration uses a custom logging format to add additional information about upstreams, response time and status
+
+```
+    log_format upstreaminfo '{{ if $cfg.useProxyProtocol }}$proxy_protocol_addr{{ else }}$remote_addr{{ end }} - '
+        '[$proxy_add_x_forwarded_for] - $remote_user [$time_local] "$request" $status $body_bytes_sent "$http_referer" "$http_user_agent" '
+        '$request_length $request_time [$proxy_upstream_name] $upstream_addr $upstream_response_length $upstream_response_time $upstream_status';
+```
+
+Sources:
+
+- [upstream variables](http://nginx.org/en/docs/http/ngx_http_upstream_module.html#variables)
+- [embedded variables](http://nginx.org/en/docs/http/ngx_http_core_module.html#variables)
+
+Description:
+
+- `$proxy_protocol_addr`: if PROXY protocol is enabled
+- `$remote_addr`: if PROXY protocol is disabled (default)
+- `$proxy_add_x_forwarded_for`: the `X-Forwarded-For` client request header field with the $remote_addr variable appended to it, separated by a comma
+- `$remote_user`: user name supplied with the Basic authentication
+- `$time_local`: local time in the Common Log Format
+- `$request`: full original request line
+- `$status`: response status
+- `$body_bytes_sent`: number of bytes sent to a client, not counting the response header
+- `$http_referer`: value of the Referer header
+- `$http_user_agent`: value of User-Agent header
+- `$request_length`: request length (including request line, header, and request body)
+- `$request_time`: time elapsed since the first bytes were read from the client
+- `$proxy_upstream_name`: name of the upstream. The format is `upstream-<namespace>-<service name>-<service port>`
+- `$upstream_addr`: keeps the IP address and port, or the path to the UNIX-domain socket of the upstream server. If several servers were contacted during request processing, their addresses are separated by commas
+- `$upstream_response_length`: keeps the length of the response obtained from the upstream server
+- `$upstream_response_time`: keeps time spent on receiving the response from the upstream server; the time is kept in seconds with millisecond resolution
+- `$upstream_status`: keeps status code of the response obtained from the upstream server