This exporter should have the option to expose response times as a histogram, rather than a simple average. The dataset to support this feature is already available in the upstreamZones. requestMsecs.msecs data structure from VTS.

Proposed Interface: An optional command line flag -nginx.response.histogram_buckets is added, and takes a comma separated list of integers as an argument. When declared, two additional metrics are implemented: {NAMESPACE}_filter_responses and {NAMESPACE}_upstream_responses. They are both histograms with bucket sizes from the input flag.

Note: I am actively building feature; any comments on the interface please let me know!