Multiple formats support

[pawellrus]

Is your feature request related to a problem? Please describe.
Some log strings doesn't contain $upstream_response_time value. So exporter throws many errors like "error while parsing $upstream_response_time: value '' could not be parsed into float"

Describe the solution you'd like
I would be nice if exporter could parse string against several formats (without $upstream_response_time for example) and select more apropriate format for each string.

[martin-helmich]

Thanks for the suggestion! 👍 The exporter was built under the general assumption that it would be fed uniform log lines. Supporting multiple log formats in a single file is not a priority for me ATM, but I'd be willing to accept pull requests for this feature, provided that they're backwards-compatible and have test coverage.

[pawellrus]

@martin-helmich, hello. Another one question regarding this issue. If we can have only one format template, may be we can define possible null values inside. I mean something like that:

format = "$remote_addr - $remote_user [$time_local] \"$request\" ($status|) ($body_bytes_sent|) \"($http_referer|)\" \"($http_user_agent|)\" \"($http_x_forwarded_for|)\""

Or it should not work?

UPD: already tested this - not possible. Seems that only way to get rid of exceptions like "error while parsing $upstream_response_time: value '' could not be parsed into float" is to implement multiple formats. :(

[Nereis]

You may want to try to define your nginx pattern with the nullable field at the end. It may work since the exporter won't have any else to parse.