Merge pull request #201 from prometheus/beorn7/doc

Document the issues of InstrumentHandler
This commit is contained in:
Björn Rabenstein 2016-05-17 11:07:30 +02:00
commit d38f1ef46f
2 changed files with 34 additions and 11 deletions

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@ -57,12 +57,31 @@ func nowSeries(t ...time.Time) nower {
// has a constant label named "handler" with the provided handlerName as
// value. http_requests_total is a metric vector partitioned by HTTP method
// (label name "method") and HTTP status code (label name "code").
//
// Note that InstrumentHandler has several issues:
//
// - It uses Summaries rather than Histograms. Summaries are not useful if
// aggregation accross multiple instances is required.
//
// - It uses microseconds as unit, which is deprecated and should be reploced by
// seconds.
//
// - The size of the request is calculated in a separate goroutine. Since this
// calculatior requires access to the request header, it creates a race with
// any writes to the header performed during request handling.
// httputil.ReverseProxy is a prominent example for a handler
// performing such writes.
//
// Upcoming versions of this package will provide ways of instrumenting HTTP
// handlers that are more flexible and have fewer issues. Consider this function
// DEPRECATED and prefer direct instrumentation in the meantime.
func InstrumentHandler(handlerName string, handler http.Handler) http.HandlerFunc {
return InstrumentHandlerFunc(handlerName, handler.ServeHTTP)
}
// InstrumentHandlerFunc wraps the given function for instrumentation. It
// otherwise works in the same way as InstrumentHandler.
// otherwise works in the same way as InstrumentHandler (and shares the same
// issues).
func InstrumentHandlerFunc(handlerName string, handlerFunc func(http.ResponseWriter, *http.Request)) http.HandlerFunc {
return InstrumentHandlerFuncWithOpts(
SummaryOpts{
@ -73,13 +92,13 @@ func InstrumentHandlerFunc(handlerName string, handlerFunc func(http.ResponseWri
)
}
// InstrumentHandlerWithOpts works like InstrumentHandler but provides more
// flexibility (at the cost of a more complex call syntax). As
// InstrumentHandler, this function registers four metric collectors, but it
// uses the provided SummaryOpts to create them. However, the fields "Name" and
// "Help" in the SummaryOpts are ignored. "Name" is replaced by
// "requests_total", "request_duration_microseconds", "request_size_bytes", and
// "response_size_bytes", respectively. "Help" is replaced by an appropriate
// InstrumentHandlerWithOpts works like InstrumentHandler (and shares the same
// issues) but provides more flexibility (at the cost of a more complex call
// syntax). As InstrumentHandler, this function registers four metric
// collectors, but it uses the provided SummaryOpts to create them. However, the
// fields "Name" and "Help" in the SummaryOpts are ignored. "Name" is replaced
// by "requests_total", "request_duration_microseconds", "request_size_bytes",
// and "response_size_bytes", respectively. "Help" is replaced by an appropriate
// help string. The names of the variable labels of the http_requests_total
// CounterVec are "method" (get, post, etc.), and "code" (HTTP status code).
//
@ -102,9 +121,10 @@ func InstrumentHandlerWithOpts(opts SummaryOpts, handler http.Handler) http.Hand
return InstrumentHandlerFuncWithOpts(opts, handler.ServeHTTP)
}
// InstrumentHandlerFuncWithOpts works like InstrumentHandlerFunc but provides
// more flexibility (at the cost of a more complex call syntax). See
// InstrumentHandlerWithOpts for details how the provided SummaryOpts are used.
// InstrumentHandlerFuncWithOpts works like InstrumentHandlerFunc (and shares
// the same issues) but provides more flexibility (at the cost of a more complex
// call syntax). See InstrumentHandlerWithOpts for details how the provided
// SummaryOpts are used.
func InstrumentHandlerFuncWithOpts(opts SummaryOpts, handlerFunc func(http.ResponseWriter, *http.Request)) http.HandlerFunc {
reqCnt := NewCounterVec(
CounterOpts{

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@ -84,6 +84,9 @@ const (
// Handler returns the HTTP handler for the global Prometheus registry. It is
// already instrumented with InstrumentHandler (using "prometheus" as handler
// name). Usually the handler is used to handle the "/metrics" endpoint.
//
// Please note the issues described in the doc comment of InstrumentHandler. You
// might want to consider using UninstrumentedHandler instead.
func Handler() http.Handler {
return InstrumentHandler("prometheus", defRegistry)
}