frostfs-http-gw/metrics.go

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package main
import (
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"github.com/fasthttp/router"
"github.com/nspcc-dev/neofs-http-gw/response"
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"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/common/expfmt"
"github.com/valyala/fasthttp"
"go.uber.org/zap"
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)
func attachMetrics(r *router.Router, l *zap.Logger) {
r.GET("/metrics/", metricsHandler(prometheus.DefaultGatherer, l))
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}
func metricsHandler(reg prometheus.Gatherer, logger *zap.Logger) fasthttp.RequestHandler {
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var (
inFlightSem chan struct{}
errCnt = prometheus.NewCounterVec(
prometheus.CounterOpts{
Name: "promhttp_metric_handler_errors_total",
Help: "Total number of internal errors encountered by the promhttp metric handler.",
},
[]string{"cause"},
)
)
h := fasthttp.RequestHandler(func(c *fasthttp.RequestCtx) {
if inFlightSem != nil {
select {
case inFlightSem <- struct{}{}: // All good, carry on.
defer func() { <-inFlightSem }()
default:
response.Error(c, "Limit of concurrent requests reached, try again later.", fasthttp.StatusServiceUnavailable)
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return
}
}
mfs, err := reg.Gather()
if err != nil {
if logger != nil {
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panic("error gathering metrics:" + err.Error())
}
errCnt.WithLabelValues("gathering").Inc()
response.Error(c, err.Error(), fasthttp.StatusServiceUnavailable)
return
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}
contentType := expfmt.FmtText
c.SetContentType(string(contentType))
enc := expfmt.NewEncoder(c, contentType)
var lastErr error
// handleError handles the error according to opts.ErrorHandling
// and returns true if we have to abort after the handling.
handleError := func(err error) bool {
if err == nil {
return false
}
lastErr = err
if logger != nil {
logger.Error("encoding and sending metric family", zap.Error(err))
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}
errCnt.WithLabelValues("encoding").Inc()
response.Error(c, err.Error(), fasthttp.StatusServiceUnavailable)
return true
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}
for _, mf := range mfs {
if handleError(enc.Encode(mf)) {
return
}
}
if closer, ok := enc.(expfmt.Closer); ok {
// This in particular takes care of the final "# EOF\n" line for OpenMetrics.
if handleError(closer.Close()) {
return
}
}
handleError(lastErr)
})
return h
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}