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Group servers in upstream #90

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Group servers in upstream #90

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29 changes: 28 additions & 1 deletion nginx_vts_exporter.go
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Original file line number Diff line number Diff line change
Expand Up @@ -175,6 +175,31 @@ func newCacheMetric(metricName string, docString string, labels []string) *prome
)
}

func groupUpstreamsByServer(upstreamList []Upstream) []Upstream {
groupedByServer := make([]Upstream, 0)
upstreamsMap := make(map[string]int)

for _, upstream := range upstreamList {
if index, exists := upstreamsMap[upstream.Server]; exists {
groupedByServer[index].RequestCounter += upstream.RequestCounter
groupedByServer[index].InBytes += upstream.InBytes
groupedByServer[index].OutBytes += upstream.OutBytes
groupedByServer[index].Responses.OneXx += upstream.Responses.OneXx
groupedByServer[index].Responses.TwoXx += upstream.Responses.TwoXx
groupedByServer[index].Responses.ThreeXx += upstream.Responses.ThreeXx
groupedByServer[index].Responses.FourXx += upstream.Responses.FourXx
groupedByServer[index].Responses.FiveXx += upstream.Responses.FiveXx
groupedByServer[index].RequestMsec = (groupedByServer[index].RequestMsec + upstream.RequestMsec) / 2
groupedByServer[index].ResponseMsec = (groupedByServer[index].ResponseMsec + upstream.ResponseMsec) / 2
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upstream.ResponseMsec seems to be computed as an average, but computing an average on top of averages cannot technically be considered an average. For example, I think for a single server in upstream with ResponseMsec=42ms the aggregated ResponseMsec would be 21ms ((0 + 42) / 2 = 21), which is different from the expected 42ms.

I'd convert the averages back to the sums of times (assuming that RequestCounter is the denominator of the averages), and then compute the aggregated average using the sums, something like this:

if (groupedByServer[index].RequestCounter + upstream.RequestCounter) > 0 {
	groupedByServer[index].RequestMsec = (groupedByServer[index].RequestMsec * groupedByServer[index].RequestCounter + upstream.RequestMsec * upstream.RequestCounter) / (groupedByServer[index].RequestCounter + upstream.RequestCounter)
	groupedByServer[index].ResponseMsec = (groupedByServer[index].ResponseMsec * groupedByServer[index].RequestCounter + upstream.ResponseMsec * upstream.RequestCounter) / (groupedByServer[index].RequestCounter + upstream.RequestCounter)
}
groupedByServer[index].RequestCounter += upstream.RequestCounter  // note that this increment has to happen *after* the averages

Despite this little issue -- thank you for the great patch!

(Note, I'm not a maintainer of this project, I just faced the same issue and have reused your helpful solution).

} else {
groupedByServer = append(groupedByServer, upstream)
upstreamsMap[upstream.Server] = len(groupedByServer) - 1
}
}

return groupedByServer
}

func NewExporter(uri string) *Exporter {
return &Exporter{
URI: uri,
Expand Down Expand Up @@ -281,7 +306,9 @@ func (e *Exporter) Collect(ch chan<- prometheus.Metric) {

// UpstreamZones
for name, upstreamList := range nginxVtx.UpstreamZones {
for _, s := range upstreamList {
groupedUpstreamsByServer := groupUpstreamsByServer(upstreamList)

for _, s := range groupedUpstreamsByServer {
ch <- prometheus.MustNewConstMetric(e.upstreamMetrics["responseMsec"], prometheus.GaugeValue, float64(s.ResponseMsec), name, s.Server)
ch <- prometheus.MustNewConstMetric(e.upstreamMetrics["requestMsec"], prometheus.GaugeValue, float64(s.RequestMsec), name, s.Server)

Expand Down