Summary

Although inadequately documented in OpenTSDB, the syntax for expressing the rate option "dropResets: true" is in fact rate{dropcounter} as can be seen in QueryRpc.java in the OpenTSDB source. Unfortunately, Bosun parses the OpenTSDB query string itself and doesn't recognise this syntax, silently dropping {dropcounter} from the query it sends to OpenTSDB.

Demonstration

For example, if I go into the Bosun expression editor and run this query:

q("sum:1m-last-null:rate{dropcounter}:slingshot.services.falcon.proxy.hrsp_5xx", "10m", "1m")

I see listed the queries performed:

Queries
end=2019/04/16-02:30:00&m=sum:1m-last-null:rate:slingshot.services.falcon.proxy.hrsp_5xx&start=2019/04/16-02:21:00

The {dropcounter} option has vanished, contrary to my expectations.

By contrast, if I run this query:

q("sum:1m-last-null:rate{counter}:slingshot.services.falcon.proxy.hrsp_5xx", "10m", "1m")

I see this instead:

Queries
end=2019/04/16-02:30:00&m=sum:1m-last-null:rate{counter}:slingshot.services.falcon.proxy.hrsp_5xx&start=2019/04/16-02:21:00

This time the rate option {counter} is preserved, as expected.

Analysis

Bosun's OpenTSDB code does not know about dropResets:
tsdb.go:453-456:

type RateOptions struct {
	Counter    bool  `json:"counter,omitempty"`
	CounterMax int64 `json:"counterMax,omitempty"`
	ResetValue int64 `json:"resetValue,omitempty"`
}

Nor recognise dropcounter:
tsdb.go:519:

q.RateOptions.Counter = sp[0] == "counter"