Apache log format

The WMF Apache access log format is derived from the cache log format. It has tab-separated fields.

Field#	Description	Details
1	time stamp	The time at which the request started, in ISO 8601 format, according to the server's clock.
2	Request service time	Integer number of microseconds
3	Client IP	You might want to override this with the original client IP (field 17 below).
4	Request handler, HTTP status code	The Apache request handler, then a slash, then the HTTP status code, e.g. cgi-script/200
5	Response size	Size of response in bytes, excluding HTTP headers.
6	Request method	GET, POST, etc
7	URL	The URL, concatenated from the host header, the path and the query string. The protocol is always http, even if mod_ssl was used. In theory we could use SetEnvIf with "SSLOptions StdEnvVars", but the latter has a high performance overhead, according to the documentation.
8	Empty	For compatibility with the cache log format, this field is always just a hyphen.
9	MIME content type	The Content-Type response header
10	Referer header
11	X-Forwarded-For header	This field should only be respected if the client IP (see above) is a known good IP (i.e.: in $wgSquidServersNoPurge of wmf-config/squid.php of operations/mediawiki-config).
12	User-Agent header
13	Accept_Language
14	X-Analytics	General purpose header for instrumentation, which received its own page at X-Analytics.
15	User	The username as determined by HTTP authentication
16	User: Response header	The username as determined by the server and added as the HTTP User: header. Since 2019-03-20
17	Original client IP or if local Envoy proxy, the local IP	The original client IP as determined by mod_remoteip, which can walk X-Forwarded-For headers. This module currently needs to be configured on a per-site basis to give good results. If the module is not present, this will be a copy of field 3.
18	Request ID	Internally we generate a request ID header, X-Request-Id, that should allow to trace a request across logs of various services. Since 2020-02-03
19	Original client IP	The original client IP as determined by mod_remoteip, which can walk X-Forwarded-For headers. This module currently needs to be configured on a per-site basis to give good results. If the module is not present, this will be a copy of field 3.