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Metrics

In this quickstart, we’ll glean insights from code segments and learn how to:

  1. Collect metrics using OpenCensus Metrics and Tags
  2. Register and enable an exporter for any backend of our choice
  3. View the metrics on the backend of our choice

Requirements

For assistance setting up Prometheus, Click here for a guided codelab.

You can swap out any other exporter from the list of Go exporters

Installation

OpenCensus: go get -u -v go.opencensus.io/...

Prometheus exporter: go get -u -v contrib.go.opencensus.io/exporter/prometheus

Brief Overview

By the end of this tutorial, we will do these four things to obtain metrics using OpenCensus:

  1. Create quantifiable metrics (numerical) that we will record
  2. Create tags that we will associate with our metrics
  3. Organize our metrics, similar to writing a report, in to a View
  4. Export our views to a backend (Prometheus in this case)

Getting Started

Unsure how to write and execute Go code? Click here.

We will be a simple “read-evaluate-print-loop” (REPL) app. In there we’ll collect some metrics to observe the work that is going on within this code, such as:

First, create a file called repl.go.

touch repl.go

Next, put the following code inside of repl.go:

package main

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"log"
	"os"
)

func main() {
	// In a REPL:
	//   1. Read input
	//   2. process input
	br := bufio.NewReader(os.Stdin)

	// repl is the read, evaluate, print, loop
	for {
		if err := readEvaluateProcess(br); err != nil {
			if err == io.EOF {
				return
			}
			log.Fatal(err)
		}
	}
}

// readEvaluateProcess reads a line from the input reader and
// then processes it. It returns an error if any was encountered.
func readEvaluateProcess(br *bufio.Reader) (terr error) {
	fmt.Printf("> ")
	line, _, err := br.ReadLine()
	if err != nil {
		return err
	}

	out, err := processLine(line)
	if err != nil {
		return err
	}
	fmt.Printf("< %s\n\n", out)
	return nil
}

// processLine takes in a line of text and
// transforms it. Currently it just capitalizes it.
func processLine(in []byte) (out []byte, err error) {
	return bytes.ToUpper(in), nil
}

You can run the code via go run repl.go.

Enable Metrics

Import Packages

To enable metrics, we’ll import a couple of packages:

import (
	"bufio"
	"bytes"
	"context"
	"fmt"
	"io"
	"log"
	"os"
	"time"

	"go.opencensus.io/stats"
	"go.opencensus.io/tag"
)
package main

import (
	"bufio"
	"bytes"
	"context"
	"fmt"
	"io"
	"log"
	"os"
	"time"

	"go.opencensus.io/stats"
	"go.opencensus.io/tag"
)

func main() {
	// In a REPL:
	//   1. Read input
	//   2. process input
	br := bufio.NewReader(os.Stdin)

	// repl is the read, evaluate, print, loop
	for {
		if err := readEvaluateProcess(br); err != nil {
			if err == io.EOF {
				return
			}
			log.Fatal(err)
		}
	}
}

// readEvaluateProcess reads a line from the input reader and
// then processes it. It returns an error if any was encountered.
func readEvaluateProcess(br *bufio.Reader) (terr error) {
	fmt.Printf("> ")
	line, _, err := br.ReadLine()
	if err != nil {
		return err
	}

	out, err := processLine(line)
	if err != nil {
		return err
	}
	fmt.Printf("< %s\n\n", out)
	return nil
}

// processLine takes in a line of text and
// transforms it. Currently it just capitalizes it.
func processLine(in []byte) (out []byte, err error) {
	return bytes.ToUpper(in), nil
}

Create Metrics

First, we will create the variables needed to later record our metrics.

var (
	// The latency in milliseconds
	MLatencyMs = stats.Float64("repl/latency", "The latency in milliseconds per REPL loop", "ms")

	// Counts/groups the lengths of lines read in.
	MLineLengths = stats.Int64("repl/line_lengths", "The distribution of line lengths", "By")
)
package main

import (
	"bufio"
	"bytes"
	"context"
	"fmt"
	"io"
	"log"
	"os"
	"time"

	"go.opencensus.io/stats"
	"go.opencensus.io/tag"
)

var (
	// The latency in milliseconds
	MLatencyMs = stats.Float64("repl/latency", "The latency in milliseconds per REPL loop", "ms")

	// Counts/groups the lengths of lines read in.
	MLineLengths = stats.Int64("repl/line_lengths", "The distribution of line lengths", "By")
)

func main() {
	// In a REPL:
	//   1. Read input
	//   2. process input
	br := bufio.NewReader(os.Stdin)

	// repl is the read, evaluate, print, loop
	for {
		if err := readEvaluateProcess(br); err != nil {
			if err == io.EOF {
				return
			}
			log.Fatal(err)
		}
	}
}

// readEvaluateProcess reads a line from the input reader and
// then processes it. It returns an error if any was encountered.
func readEvaluateProcess(br *bufio.Reader) (terr error) {
	fmt.Printf("> ")
	line, _, err := br.ReadLine()
	if err != nil {
		return err
	}

	out, err := processLine(line)
	if err != nil {
		return err
	}
	fmt.Printf("< %s\n\n", out)
	return nil
}

// processLine takes in a line of text and
// transforms it. Currently it just capitalizes it.
func processLine(in []byte) (out []byte, err error) {
	return bytes.ToUpper(in), nil
}

Create Tags

Now we will create the variable later needed to add extra text meta-data to our metrics.

var (
	KeyMethod, _ = tag.NewKey("method")
	KeyStatus, _ = tag.NewKey("status")
	KeyError, _  = tag.NewKey("error")
)
package main

import (
	"bufio"
	"bytes"
	"context"
	"fmt"
	"io"
	"log"
	"os"
	"time"

	"go.opencensus.io/stats"
	"go.opencensus.io/tag"
)

var (
	// The latency in milliseconds
	MLatencyMs = stats.Float64("repl/latency", "The latency in milliseconds per REPL loop", "ms")

	// Counts/groups the lengths of lines read in.
	MLineLengths = stats.Int64("repl/line_lengths", "The distribution of line lengths", "By")
)

var (
	KeyMethod, _ = tag.NewKey("method")
	KeyStatus, _ = tag.NewKey("status")
	KeyError, _  = tag.NewKey("error")
)

func main() {
	// In a REPL:
	//   1. Read input
	//   2. process input
	br := bufio.NewReader(os.Stdin)

	// repl is the read, evaluate, print, loop
	for {
		if err := readEvaluateProcess(br); err != nil {
			if err == io.EOF {
				return
			}
			log.Fatal(err)
		}
	}
}

// readEvaluateProcess reads a line from the input reader and
// then processes it. It returns an error if any was encountered.
func readEvaluateProcess(br *bufio.Reader) (terr error) {
	fmt.Printf("> ")
	line, _, err := br.ReadLine()
	if err != nil {
		return err
	}

	out, err := processLine(line)
	if err != nil {
		return err
	}
	fmt.Printf("< %s\n\n", out)
	return nil
}

// processLine takes in a line of text and
// transforms it. Currently it just capitalizes it.
func processLine(in []byte) (out []byte, err error) {
	return bytes.ToUpper(in), nil
}

We will later use this tag, called KeyMethod, to record what method is being invoked. In our scenario, we will only use it to record that “repl” is calling our data.

Again, this is arbitrary and purely up the user. For example, if we wanted to track what operating system a user is using, we could do so like this:

osKey, _ := tag.NewKey("operating_system")

Later, when we use osKey, we will be given an opportunity to enter values such as “windows” or “mac”.

Inserting Tags

Now we will insert a specific tag called “repl”. It will give us a new context.Context ctx which we will use while we later record our metrics. This ctx has all tags that have previously been inserted, thus allowing for context propagation.

For example

ctx, _ := tag.New(context.Background(), tag.Insert(KeyMethod, "repl"), tag.Insert(KeyStatus, "OK"))

and for complete usage:

func readEvaluateProcess(br *bufio.Reader) (terr error) {
	ctx, err := tag.New(context.Background(), tag.Insert(KeyMethod, "repl"), tag.Insert(KeyStatus, "OK"))
	if err != nil {
		return err
	}

	fmt.Printf("> ")
	line, _, err := br.ReadLine()
	if err != nil {
		return err
	}

	out, err := processLine(line)
	if err != nil {
		return err
	}
	fmt.Printf("< %s\n\n", out)
	return nil
}
package main

import (
	"bufio"
	"bytes"
	"context"
	"fmt"
	"io"
	"log"
	"os"
	"time"

	"go.opencensus.io/stats"
	"go.opencensus.io/tag"
)

var (
	// The latency in milliseconds
	MLatencyMs = stats.Float64("repl/latency", "The latency in milliseconds per REPL loop", "ms")

	// Counts/groups the lengths of lines read in.
	MLineLengths = stats.Int64("repl/line_lengths", "The distribution of line lengths", "By")
)

var (
	KeyMethod, _ = tag.NewKey("method")
	KeyStatus, _ = tag.NewKey("status")
	KeyError, _  = tag.NewKey("error")
)

func main() {
	// In a REPL:
	//   1. Read input
	//   2. process input
	br := bufio.NewReader(os.Stdin)

	// repl is the read, evaluate, print, loop
	for {
		if err := readEvaluateProcess(br); err != nil {
			if err == io.EOF {
				return
			}
			log.Fatal(err)
		}
	}
}

// readEvaluateProcess reads a line from the input reader and
// then processes it. It returns an error if any was encountered.
func readEvaluateProcess(br *bufio.Reader) (terr error) {
	ctx, err := tag.New(context.Background(), tag.Insert(KeyMethod, "repl"), tag.Insert(KeyStatus, "OK"))
	if err != nil {
		return err
	}

	fmt.Printf("> ")
	line, _, err := br.ReadLine()
	if err != nil {
		return err
	}

	out, err := processLine(line)
	if err != nil {
		return err
	}
	fmt.Printf("< %s\n\n", out)
	return nil
}

// processLine takes in a line of text and
// transforms it. Currently it just capitalizes it.
func processLine(in []byte) (out []byte, err error) {
	return bytes.ToUpper(in), nil
}

When recording metrics, we will need the ctx from tag.New. We will be recording metrics in processLine, so let’s go ahead and make ctx available now.

// ...
out, err := processLine(ctx, line)

// ...
func processLine(ctx context.Context, in []byte) (out []byte, err error) {
  // ...
}
package main

import (
	"bufio"
	"bytes"
	"context"
	"fmt"
	"io"
	"log"
	"os"
	"time"

	"go.opencensus.io/stats"
	"go.opencensus.io/tag"
)

var (
	// The latency in milliseconds
	MLatencyMs = stats.Float64("repl/latency", "The latency in milliseconds per REPL loop", "ms")

	// Counts/groups the lengths of lines read in.
	MLineLengths = stats.Int64("repl/line_lengths", "The distribution of line lengths", "By")
)

var (
	KeyMethod, _ = tag.NewKey("method")
	KeyStatus, _ = tag.NewKey("status")
	KeyError, _  = tag.NewKey("error")
)

func main() {
	// In a REPL:
	//   1. Read input
	//   2. process input
	br := bufio.NewReader(os.Stdin)

	// repl is the read, evaluate, print, loop
	for {
		if err := readEvaluateProcess(br); err != nil {
			if err == io.EOF {
				return
			}
			log.Fatal(err)
		}
	}
}

// readEvaluateProcess reads a line from the input reader and
// then processes it. It returns an error if any was encountered.
func readEvaluateProcess(br *bufio.Reader) (terr error) {
	fmt.Printf("> ")
	line, _, err := br.ReadLine()
	if err != nil {
		return err
	}

	out, err := processLine(ctx, line)
	if err != nil {
		return err
	}
	fmt.Printf("< %s\n\n", out)
	return nil
}

// processLine takes in a line of text and
// transforms it. Currently it just capitalizes it.
func processLine(ctx context.Context, in []byte) (out []byte, err error) {

	return bytes.ToUpper(in), nil
}

Recording Metrics

Now we will record the desired metrics. To do so, we will use stats.Record and pass in our ctx and previously instantiated metrics variables.

func readEvaluateProcess(br *bufio.Reader) (terr error) {
	startTime := time.Now()
	ctx, err := tag.New(context.Background(), tag.Insert(KeyMethod, "repl"), tag.Insert(KeyStatus, "OK"))
	if err != nil {
		return err
	}

	defer func() {
		if terr != nil {
			ctx, _ = tag.New(ctx, tag.Upsert(KeyStatus, "ERROR"),
				tag.Upsert(KeyError, terr.Error()))
		}

		stats.Record(ctx, MLatencyMs.M(sinceInMilliseconds(startTime)))
	}()

	fmt.Printf("> ")
	line, _, err := br.ReadLine()
	if err != nil {
		if err != io.EOF {
			return err
		}
		log.Fatal(err)
	}

	out, err := processLine(ctx, line)
	if err != nil {
		return err
	}
	fmt.Printf("< %s\n\n", out)
	return nil
}

// processLine takes in a line of text and
// transforms it. Currently it just capitalizes it.
func processLine(ctx context.Context, in []byte) (out []byte, err error) {
	startTime := time.Now()
	defer func() {
		stats.Record(ctx, MLatencyMs.M(sinceInMilliseconds(startTime)),
			MLineLengths.M(int64(len(in))))
	}()

	return bytes.ToUpper(in), nil
}

func sinceInMilliseconds(startTime time.Time) float64 {
	return float64(time.Since(startTime).Nanoseconds()) / 1e6
}
package main

import (
	"bufio"
	"bytes"
	"context"
	"fmt"
	"io"
	"log"
	"os"
	"time"

	"go.opencensus.io/stats"
	"go.opencensus.io/tag"
)

var (
	// The latency in milliseconds
	MLatencyMs = stats.Float64("repl/latency", "The latency in milliseconds per REPL loop", "ms")

	// Counts/groups the lengths of lines read in.
	MLineLengths = stats.Int64("repl/line_lengths", "The distribution of line lengths", "By")
)

var (
	KeyMethod, _ = tag.NewKey("method")
	KeyStatus, _ = tag.NewKey("status")
	KeyError, _  = tag.NewKey("error")
)

func main() {
	// In a REPL:
	//   1. Read input
	//   2. process input
	br := bufio.NewReader(os.Stdin)

	// repl is the read, evaluate, print, loop
	for {
		if err := readEvaluateProcess(br); err != nil {
			if err == io.EOF {
				return
			}
			log.Fatal(err)
		}
	}
}

// readEvaluateProcess reads a line from the input reader and
// then processes it. It returns an error if any was encountered.
func readEvaluateProcess(br *bufio.Reader) (terr error) {
	startTime := time.Now()
	ctx, err := tag.New(context.Background(), tag.Insert(KeyMethod, "repl"), tag.Insert(KeyStatus, "OK"))
	if err != nil {
		return err
	}

	defer func() {
		if terr != nil {
			ctx, _ = tag.New(ctx, tag.Upsert(KeyStatus, "ERROR"),
				tag.Upsert(KeyError, terr.Error()))
		}

		stats.Record(ctx, MLatencyMs.M(sinceInMilliseconds(startTime)))
	}()

	fmt.Printf("> ")
	line, _, err := br.ReadLine()
	if err != nil {
		if err != io.EOF {
			return err
		}
		log.Fatal(err)
	}

	out, err := processLine(ctx, line)
	if err != nil {
		return err
	}
	fmt.Printf("< %s\n\n", out)
	return nil
}

// processLine takes in a line of text and
// transforms it. Currently it just capitalizes it.
func processLine(ctx context.Context, in []byte) (out []byte, err error) {
	startTime := time.Now()
	defer func() {
		stats.Record(ctx, MLatencyMs.M(sinceInMilliseconds(startTime)),
			MLineLengths.M(int64(len(in))))
	}()

	return bytes.ToUpper(in), nil
}

func sinceInMilliseconds(startTime time.Time) float64 {
	return float64(time.Since(startTime).Nanoseconds()) / 1e6
}

Enable Views

We will be adding the View package: "go.opencensus.io/stats/view"

Import Packages

import (
	"bufio"
	"bytes"
	"context"
	"fmt"
	"io"
	"log"
	"os"
	"time"

	"go.opencensus.io/stats"
	"go.opencensus.io/stats/view"
	"go.opencensus.io/tag"
)
package main

import (
	"bufio"
	"bytes"
	"context"
	"fmt"
	"io"
	"log"
	"os"
	"time"

	"go.opencensus.io/stats"
	"go.opencensus.io/stats/view"
	"go.opencensus.io/tag"
)

var (
	// The latency in milliseconds
	MLatencyMs = stats.Float64("repl/latency", "The latency in milliseconds per REPL loop", "ms")

	// Counts/groups the lengths of lines read in.
	MLineLengths = stats.Int64("repl/line_lengths", "The distribution of line lengths", "By")
)

var (
	KeyMethod, _ = tag.NewKey("method")
	KeyStatus, _ = tag.NewKey("status")
	KeyError, _  = tag.NewKey("error")
)

func main() {
	// In a REPL:
	//   1. Read input
	//   2. process input
	br := bufio.NewReader(os.Stdin)

	// repl is the read, evaluate, print, loop
	for {
		if err := readEvaluateProcess(br); err != nil {
			if err == io.EOF {
				return
			}
			log.Fatal(err)
		}
	}
}

// readEvaluateProcess reads a line from the input reader and
// then processes it. It returns an error if any was encountered.
func readEvaluateProcess(br *bufio.Reader) (terr error) {
	startTime := time.Now()
	ctx, err := tag.New(context.Background(), tag.Insert(KeyMethod, "repl"), tag.Insert(KeyStatus, "OK"))
	if err != nil {
		return err
	}

	defer func() {
		if terr != nil {
			ctx, _ = tag.New(ctx, tag.Upsert(KeyStatus, "ERROR"),
				tag.Upsert(KeyError, terr.Error()))
		}

		stats.Record(ctx, MLatencyMs.M(sinceInMilliseconds(startTime)))
	}()

	fmt.Printf("> ")
	line, _, err := br.ReadLine()
	if err != nil {
		if err != io.EOF {
			return err
		}
		log.Fatal(err)
	}

	out, err := processLine(ctx, line)
	if err != nil {
		return err
	}
	fmt.Printf("< %s\n\n", out)
	return nil
}

// processLine takes in a line of text and
// transforms it. Currently it just capitalizes it.
func processLine(ctx context.Context, in []byte) (out []byte, err error) {
	startTime := time.Now()
	defer func() {
		stats.Record(ctx, MLatencyMs.M(sinceInMilliseconds(startTime)),
			MLineLengths.M(int64(len(in))))
	}()

	return bytes.ToUpper(in), nil
}

func sinceInMilliseconds(startTime time.Time) float64 {
	return float64(time.Since(startTime).Nanoseconds()) / 1e6
}

Create Views

We now determine how our metrics will be organized by creating Views.

var (
	LatencyView = &view.View{
		Name:        "demo/latency",
		Measure:     MLatencyMs,
		Description: "The distribution of the latencies",

		// Latency in buckets:
		// [>=0ms, >=25ms, >=50ms, >=75ms, >=100ms, >=200ms, >=400ms, >=600ms, >=800ms, >=1s, >=2s, >=4s, >=6s]
		Aggregation: view.Distribution(0, 25, 50, 75, 100, 200, 400, 600, 800, 1000, 2000, 4000, 6000),
		TagKeys:     []tag.Key{KeyMethod}}

	LineCountView = &view.View{
		Name:        "demo/lines_in",
		Measure:     MLineLengths,
		Description: "The number of lines from standard input",
		Aggregation: view.Count(),
	}

	LineLengthView = &view.View{
		Name:        "demo/line_lengths",
		Description: "Groups the lengths of keys in buckets",
		Measure:     MLineLengths,
		// Lengths: [>=0B, >=5B, >=10B, >=15B, >=20B, >=40B, >=60B, >=80, >=100B, >=200B, >=400, >=600, >=800, >=1000]
		Aggregation: view.Distribution(0, 5, 10, 15, 20, 40, 60, 80, 100, 200, 400, 600, 800, 1000),
	}
)
package main

import (
	"bufio"
	"bytes"
	"context"
	"fmt"
	"io"
	"log"
	"os"
	"time"

	"go.opencensus.io/stats"
	"go.opencensus.io/stats/view"
	"go.opencensus.io/tag"
)

var (
	// The latency in milliseconds
	MLatencyMs = stats.Float64("repl/latency", "The latency in milliseconds per REPL loop", "ms")

	// Counts/groups the lengths of lines read in.
	MLineLengths = stats.Int64("repl/line_lengths", "The distribution of line lengths", "By")
)

var (
	KeyMethod, _ = tag.NewKey("method")
	KeyStatus, _ = tag.NewKey("status")
	KeyError, _  = tag.NewKey("error")
)

var (
	LatencyView = &view.View{
		Name:        "demo/latency",
		Measure:     MLatencyMs,
		Description: "The distribution of the latencies",

		// Latency in buckets:
		// [>=0ms, >=25ms, >=50ms, >=75ms, >=100ms, >=200ms, >=400ms, >=600ms, >=800ms, >=1s, >=2s, >=4s, >=6s]
		Aggregation: view.Distribution(0, 25, 50, 75, 100, 200, 400, 600, 800, 1000, 2000, 4000, 6000),
		TagKeys:     []tag.Key{KeyMethod}}

	LineCountView = &view.View{
		Name:        "demo/lines_in",
		Measure:     MLineLengths,
		Description: "The number of lines from standard input",
		Aggregation: view.Count(),
	}

	LineLengthView = &view.View{
		Name:        "demo/line_lengths",
		Description: "Groups the lengths of keys in buckets",
		Measure:     MLineLengths,
		// Lengths: [>=0B, >=5B, >=10B, >=15B, >=20B, >=40B, >=60B, >=80, >=100B, >=200B, >=400, >=600, >=800, >=1000]
		Aggregation: view.Distribution(0, 5, 10, 15, 20, 40, 60, 80, 100, 200, 400, 600, 800, 1000),
	}
)

func main() {
	// In a REPL:
	//   1. Read input
	//   2. process input
	br := bufio.NewReader(os.Stdin)

	// repl is the read, evaluate, print, loop
	for {
		if err := readEvaluateProcess(br); err != nil {
			if err == io.EOF {
				return
			}
			log.Fatal(err)
		}
	}
}

// readEvaluateProcess reads a line from the input reader and
// then processes it. It returns an error if any was encountered.
func readEvaluateProcess(br *bufio.Reader) (terr error) {
	startTime := time.Now()
	ctx, err := tag.New(context.Background(), tag.Insert(KeyMethod, "repl"), tag.Insert(KeyStatus, "OK"))
	if err != nil {
		return err
	}

	defer func() {
		if terr != nil {
			ctx, _ = tag.New(ctx, tag.Upsert(KeyStatus, "ERROR"),
				tag.Upsert(KeyError, terr.Error()))
		}

		stats.Record(ctx, MLatencyMs.M(sinceInMilliseconds(startTime)))
	}()

	fmt.Printf("> ")
	line, _, err := br.ReadLine()
	if err != nil {
		if err != io.EOF {
			return err
		}
		log.Fatal(err)
	}

	out, err := processLine(ctx, line)
	if err != nil {
		return err
	}
	fmt.Printf("< %s\n\n", out)
	return nil
}

// processLine takes in a line of text and
// transforms it. Currently it just capitalizes it.
func processLine(ctx context.Context, in []byte) (out []byte, err error) {
	startTime := time.Now()
	defer func() {
		stats.Record(ctx, MLatencyMs.M(sinceInMilliseconds(startTime)),
			MLineLengths.M(int64(len(in))))
	}()

	return bytes.ToUpper(in), nil
}

func sinceInMilliseconds(startTime time.Time) float64 {
	return float64(time.Since(startTime).Nanoseconds()) / 1e6
}

Register Views

We now register the views and set the reporting period.

func main() {
	// In a REPL:
	//   1. Read input
	//   2. process input
	br := bufio.NewReader(os.Stdin)

	// Register the views
	if err := view.Register(LatencyView, LineCountView, LineLengthView); err != nil {
		log.Fatalf("Failed to register views: %v", err)
	}

	// repl is the read, evaluate, print, loop
	for {
		if err := readEvaluateProcess(br); err != nil {
			if err == io.EOF {
				return
			}
			log.Fatal(err)
		}
	}
}
package main

import (
	"bufio"
	"bytes"
	"context"
	"fmt"
	"io"
	"log"
	"os"
	"time"

	"go.opencensus.io/stats"
	"go.opencensus.io/stats/view"
	"go.opencensus.io/tag"
)

var (
	// The latency in milliseconds
	MLatencyMs = stats.Float64("repl/latency", "The latency in milliseconds per REPL loop", "ms")

	// Counts/groups the lengths of lines read in.
	MLineLengths = stats.Int64("repl/line_lengths", "The distribution of line lengths", "By")
)

var (
	KeyMethod, _ = tag.NewKey("method")
	KeyStatus, _ = tag.NewKey("status")
	KeyError, _  = tag.NewKey("error")
)

var (
	LatencyView = &view.View{
		Name:        "demo/latency",
		Measure:     MLatencyMs,
		Description: "The distribution of the latencies",

		// Latency in buckets:
		// [>=0ms, >=25ms, >=50ms, >=75ms, >=100ms, >=200ms, >=400ms, >=600ms, >=800ms, >=1s, >=2s, >=4s, >=6s]
		Aggregation: view.Distribution(0, 25, 50, 75, 100, 200, 400, 600, 800, 1000, 2000, 4000, 6000),
		TagKeys:     []tag.Key{KeyMethod}}

	LineCountView = &view.View{
		Name:        "demo/lines_in",
		Measure:     MLineLengths,
		Description: "The number of lines from standard input",
		Aggregation: view.Count(),
	}

	LineLengthView = &view.View{
		Name:        "demo/line_lengths",
		Description: "Groups the lengths of keys in buckets",
		Measure:     MLineLengths,
		// Lengths: [>=0B, >=5B, >=10B, >=15B, >=20B, >=40B, >=60B, >=80, >=100B, >=200B, >=400, >=600, >=800, >=1000]
		Aggregation: view.Distribution(0, 5, 10, 15, 20, 40, 60, 80, 100, 200, 400, 600, 800, 1000),
	}
)

func main() {
	// In a REPL:
	//   1. Read input
	//   2. process input
	br := bufio.NewReader(os.Stdin)

	// Register the views
	if err := view.Register(LatencyView, LineCountView, LineLengthView); err != nil {
		log.Fatalf("Failed to register views: %v", err)
	}

	// repl is the read, evaluate, print, loop
	for {
		if err := readEvaluateProcess(br); err != nil {
			if err == io.EOF {
				return
			}
			log.Fatal(err)
		}
	}
}

// readEvaluateProcess reads a line from the input reader and
// then processes it. It returns an error if any was encountered.
func readEvaluateProcess(br *bufio.Reader) (terr error) {
	ctx, err := tag.New(context.Background(), tag.Insert(KeyMethod, "repl"), tag.Insert(KeyStatus, "OK"))
	if err != nil {
		return err
	}

	defer func() {
		if terr != nil {
			ctx, _ = tag.New(ctx, tag.Upsert(KeyStatus, "ERROR"),
				tag.Upsert(KeyError, terr.Error()))
		}

		stats.Record(ctx, MLatencyMs.M(sinceInMilliseconds(startTime)))
	}()

	fmt.Printf("> ")
	line, _, err := br.ReadLine()
	if err != nil {
		if err != io.EOF {
			return err
		}
		log.Fatal(err)
	}

	out, err := processLine(ctx, line)
	if err != nil {
		return err
	}
	fmt.Printf("< %s\n\n", out)
	return nil
}

// processLine takes in a line of text and
// transforms it. Currently it just capitalizes it.
func processLine(ctx context.Context, in []byte) (out []byte, err error) {
	startTime := time.Now()
	defer func() {
		stats.Record(ctx, MLatencyMs.M(sinceInMilliseconds(startTime)),
			MLineLengths.M(int64(len(in))))
	}()

	return bytes.ToUpper(in), nil
}

func sinceInMilliseconds(startTime time.Time) float64 {
	return float64(time.Since(startTime).Nanoseconds()) / 1e6
}

Exporting stats

Register the views

// Register the views
if err := view.Register(LatencyView, LineCountView, LineLengthView); err != nil {
	log.Fatalf("Failed to register views: %v", err)
}

Import Packages

We will be adding the Prometheus Go exporter package package: "contrib.go.opencensus.io/exporter/prometheus"

Create the exporter

In order for our metrics to be exported to Prometheus, our application needs to be exposed as a scrape endpoint. The OpenCensus Go Prometheus exporter is an http.Handler that MUST be attached to http endpoint “/metrics”.

import (
	"log"
	"net/http"

	"contrib.go.opencensus.io/exporter/prometheus"
	"go.opencensus.io/stats/view"
)

func main() {
	pe, err := prometheus.NewExporter(prometheus.Options{
		Namespace: "ocmetricstutorial",
	})
	if err != nil {
		log.Fatalf("Failed to create the Prometheus stats exporter: %v", err)
	}

	// Now finally run the Prometheus exporter as a scrape endpoint.
	// We'll run the server on port 8888.
	go func() {
		mux := http.NewServeMux()
		mux.Handle("/metrics", pe)
		if err := http.ListenAndServe(":8888", mux); err != nil {
			log.Fatalf("Failed to run Prometheus scrape endpoint: %v", err)
		}
	}()
}

End to end code

Collectively the code will be

package main

import (
	"bufio"
	"bytes"
	"context"
	"fmt"
	"io"
	"log"
	"net/http"
	"os"
	"time"

	"contrib.go.opencensus.io/exporter/prometheus"
	"go.opencensus.io/stats"
	"go.opencensus.io/stats/view"
	"go.opencensus.io/tag"
)

var (
	// The latency in milliseconds
	MLatencyMs = stats.Float64("repl/latency", "The latency in milliseconds per REPL loop", "ms")

	// Counts/groups the lengths of lines read in.
	MLineLengths = stats.Int64("repl/line_lengths", "The distribution of line lengths", "By")
)

var (
	KeyMethod, _ = tag.NewKey("method")
	KeyStatus, _ = tag.NewKey("status")
	KeyError, _  = tag.NewKey("error")
)

var (
	LatencyView = &view.View{
		Name:        "demo/latency",
		Measure:     MLatencyMs,
		Description: "The distribution of the latencies",

		// Latency in buckets:
		// [>=0ms, >=25ms, >=50ms, >=75ms, >=100ms, >=200ms, >=400ms, >=600ms, >=800ms, >=1s, >=2s, >=4s, >=6s]
		Aggregation: view.Distribution(0, 25, 50, 75, 100, 200, 400, 600, 800, 1000, 2000, 4000, 6000),
		TagKeys:     []tag.Key{KeyMethod}}

	LineCountView = &view.View{
		Name:        "demo/lines_in",
		Measure:     MLineLengths,
		Description: "The number of lines from standard input",
		Aggregation: view.Count(),
	}

	LineLengthView = &view.View{
		Name:        "demo/line_lengths",
		Description: "Groups the lengths of keys in buckets",
		Measure:     MLineLengths,
		// Lengths: [>=0B, >=5B, >=10B, >=15B, >=20B, >=40B, >=60B, >=80, >=100B, >=200B, >=400, >=600, >=800, >=1000]
		Aggregation: view.Distribution(0, 5, 10, 15, 20, 40, 60, 80, 100, 200, 400, 600, 800, 1000),
	}
)

func main() {
	// Register the views, it is imperative that this step exists
	// lest recorded metrics will be dropped and never exported.
	if err := view.Register(LatencyView, LineCountView, LineLengthView); err != nil {
		log.Fatalf("Failed to register the views: %v", err)
	}

	// Create the Prometheus exporter.
	pe, err := prometheus.NewExporter(prometheus.Options{
		Namespace: "ocmetricstutorial",
	})
	if err != nil {
		log.Fatalf("Failed to create the Prometheus stats exporter: %v", err)
	}

	// Now finally run the Prometheus exporter as a scrape endpoint.
	// We'll run the server on port 8888.
	go func() {
		mux := http.NewServeMux()
		mux.Handle("/metrics", pe)
		if err := http.ListenAndServe(":8888", mux); err != nil {
			log.Fatalf("Failed to run Prometheus scrape endpoint: %v", err)
		}
	}()

	// In a REPL:
	//   1. Read input
	//   2. process input
	br := bufio.NewReader(os.Stdin)

	// Register the views
	if err := view.Register(LatencyView, LineCountView, LineLengthView); err != nil {
		log.Fatalf("Failed to register views: %v", err)
	}

	// repl is the read, evaluate, print, loop
	for {
		if err := readEvaluateProcess(br); err != nil {
			if err == io.EOF {
				return
			}
			log.Fatal(err)
		}
	}
}

// readEvaluateProcess reads a line from the input reader and
// then processes it. It returns an error if any was encountered.
func readEvaluateProcess(br *bufio.Reader) (terr error) {
	startTime := time.Now()
	ctx, err := tag.New(context.Background(), tag.Insert(KeyMethod, "repl"), tag.Insert(KeyStatus, "OK"))
	if err != nil {
		return err
	}

	defer func() {
		if terr != nil {
			ctx, _ = tag.New(ctx, tag.Upsert(KeyStatus, "ERROR"),
				tag.Upsert(KeyError, terr.Error()))
		}

		stats.Record(ctx, MLatencyMs.M(sinceInMilliseconds(startTime)))
	}()

	fmt.Printf("> ")
	line, _, err := br.ReadLine()
	if err != nil {
		if err != io.EOF {
			return err
		}
		log.Fatal(err)
	}

	out, err := processLine(ctx, line)
	if err != nil {
		return err
	}
	fmt.Printf("< %s\n\n", out)
	return nil
}

// processLine takes in a line of text and
// transforms it. Currently it just capitalizes it.
func processLine(ctx context.Context, in []byte) (out []byte, err error) {
	startTime := time.Now()
	defer func() {
		stats.Record(ctx, MLatencyMs.M(sinceInMilliseconds(startTime)),
			MLineLengths.M(int64(len(in))))
	}()

	return bytes.ToUpper(in), nil
}

func sinceInMilliseconds(startTime time.Time) float64 {
	return float64(time.Since(startTime).Nanoseconds()) / 1e6
}

Running the tutorial

This step involves running the tutorial application in one terminal and then Prometheus itself in another terminal.

Having properly installed go, in one terminal, please run

go run repl.go

Prometheus configuration file

To enable Prometheus to scrape from your application, we have to point it towards the tutorial application whose server is running on “localhost:8888”.

To do this, we firstly need to create a YAML file with the configuration e.g. promconfig.yaml whose contents are:

scrape_configs:
  - job_name: 'ocmetricstutorial'

    scrape_interval: 10s

    static_configs:
      - targets: ['localhost:8888']

Running Prometheus

With that file saved as promconfig.yaml we should now be able to run Prometheus like this

prometheus --config.file=promconfig.yaml

and then return to the terminal that’s running the Go metrics tutorial and generate some work by typing inside it and it will look something like:

Viewing your metrics

With the above you should now be able to navigate to the Prometheus UI at http://localhost:9090

which should show:

Resource URL
Prometheus project https://prometheus.io/
Prometheus Go exporter https://godoc.org/contrib.go.opencensus.io/exporter/prometheus
Go exporters Go exporters
OpenCensus Go Stats package https://godoc.org/go.opencensus.io/stats
OpenCensus Go Views package https://godoc.org/go.opencensus.io/stats/view