The DevOps 2.2 Toolkit by Viktor Farcic

Author:Viktor Farcic [Viktor Farcic]
Language: eng
Format: epub
Tags: COM051240 - COMPUTERS / Software Development and Engineering / Systems Analysis and Design, COM005000 - COMPUTERS / Enterprise Applications / General, COM051430 - COMPUTERS / Software Development and Engineering / Project Management
Publisher: Packt Publishing
Published: 2018-03-13T12:08:24+00:00

docker stack deploy
-c stacks/go-demo-scale.yml
go-demo

Instrumenting services using histograms and summaries

When compared with counters and gauges, histograms are much more complex. That does not mean that they are harder to implement but that the data they provide is less simple when compared with the other metric types we explored. We'll comment on them by studying a sample code and the output it provides.

We'll switch from the vfarcic/docker-flow-swarm-listener (https://github.com/vfarcic/docker-flow-swarm-listener) repository to vfarcic/go-demo (https://github.com/vfarcic/go-demo) since it provides a simple example of a histogram.

Just as with the other types of metrics, histogram also needs to be declared as a variable of the particular type:

var (

histogram = prometheus.NewHistogramVec(prometheus.HistogramOpts{

Subsystem: "http_server",

Name: "resp_time",

Help: "Request response time",

}, []string{

"service",

"code",

"method",

"path",

})

)

The objective of the metric is to record information about response times. Its labels provide additional information like the name of the service (service), the response code (code), the method of the request (method), and the path (path). All those labels together should give us a fairly accurate picture of the response times of the service, and we'll be able to filter the results using any combination of the labels.

Next is a helper function that will allow us to record metrics easily:

func recordMetrics(start time.Time, req *http.Request, code int) {

duration := time.Since(start)

histogram.With(

prometheus.Labels{

"service": serviceName,

"code": fmt.Sprintf("%d", code),

"method": req.Method,

"path": req.URL.Path,

},

).Observe(duration.Seconds())

}

The recordMetrics function accepts argument that defines the time when a request started (start), the request itself (req), and the response code (code). We're calling histogram's' Observe function with the duration of the request expressed in seconds. The duration is obtained by calculating the time passed since the value of the start variable.

Let's take a look at one of the functions that invokes recordMetrics:

func HelloServer(w http.ResponseWriter, req *http.Request) {

start := time.Now()

defer func() { recordMetrics(start, req, http.StatusOK) }()

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