OpenCensus Libraries for Go

OpenCensus Go is a Go implementation of OpenCensus, a toolkit for collecting application performance and behavior monitoring data. Currently it consists of three major components: tags, stats, and tracing.

This project is still at a very early stage of development. The API is changing rapidly, vendoring is recommended.

Installation

$ go get -u go.opencensus.io/...

Prerequisites

OpenCensus Go libraries require Go 1.8 or later.

Exporters

OpenCensus can export instrumentation data to various backends. Currently, OpenCensus supports:

• Prometheus for stats
• OpenZipkin for traces
• Stackdriver Monitoring and Trace
• Jaeger for traces
• AWS X-Ray for traces

Tags

Tags represent propagated key-value pairs. They are propagated using context.Context in the same process or can be encoded to be transmitted on the wire and decoded back to a tag.Map at the destination.

Getting a key by a name

A key is defined by its name. To use a key, a user needs to know its name and type.

// Get a key to represent user OS.
key, err := tag.NewKey("my.org/keys/user-os")
if err != nil {
	log.Fatal(err)
}

Creating tags and propagating them

Package tag provides a builder to create tag maps and put it into the current context. To propagate a tag map to downstream methods and RPCs, New will add the produced tag map to the current context. If there is already a tag map in the current context, it will be replaced.

osKey, err := tag.NewKey("my.org/keys/user-os")
if err != nil {
	log.Fatal(err)
}
userIDKey, err := tag.NewKey("my.org/keys/user-id")
if err != nil {
	log.Fatal(err)
}

ctx, err = tag.New(ctx,
	tag.Insert(osKey, "macOS-10.12.5"),
	tag.Upsert(userIDKey, "cde36753ed"),
)
if err != nil {
	log.Fatal(err)
}

Propagating a tag map in a context

If you have access to a tag.Map, you can also propagate it in the current context:

m := tag.FromContext(ctx)

In order to update existing tags from the current context, use New and pass the returned context.

ctx, err = tag.New(ctx,
	tag.Insert(osKey, "macOS-10.12.5"),
	tag.Upsert(userIDKey, "fff0989878"),
)
if err != nil {
	log.Fatal(err)
}

Stats

Measures

Measures are used for recording data points with associated units. Creating a Measure:

videoSize, err := stats.Int64("my.org/video_size", "processed video size", "MB")
if err != nil {
	log.Fatal(err)
}

Recording Measurements

Measurements are data points associated with Measures. Recording implicitly tags the set of Measurements with the tags from the provided context:

stats.Record(ctx, videoSize.M(102478))

Views

Views are how Measures are aggregated. You can think of them as queries over the set of recorded data points (Measurements).

Views have two parts: the tags to group by and the aggregation type used.

Currently four types of aggregations are supported:

• CountAggregation is used to count the number of times a sample was recorded.
• DistributionAggregation is used to provide a histogram of the values of the samples.
• SumAggregation is used to sum up all sample values.
• MeanAggregation is used to calculate the mean of sample values.

distAgg := view.DistributionAggregation([]float64{0, 1 << 32, 2 << 32, 3 << 32})
countAgg := view.CountAggregation{}
sumAgg := view.SumAggregation{}
meanAgg := view.MeanAggregation{}

Here we create a view with the DistributionAggregation over our Measure. All Measurements will be aggregated together irrespective of their tags, i.e. no grouping by tag.

err = view.Subscribe(&view.View{
	Name:        "my.org/video_size_distribution",
	Description: "distribution of processed video size over time",
	Measure:     videoSize,
	Aggregation: view.DistributionAggregation([]float64{0, 1 << 32, 2 << 32, 3 << 32}),
})
if err != nil {
	log.Fatal(err)
}

Subscribe begins collecting data for the view. Subscribed views' data will be exported via the registered exporters.

// Register an exporter to be able to retrieve
// the data from the subscribed views.
view.RegisterExporter(&exporter{})

An example logger exporter is below:

type exporter struct{}

func (e *exporter) ExportView(vd *view.Data) {
	log.Println(vd)
}

Configure the default interval between reports of collected data. This is a system wide interval and impacts all views. The default interval duration is 10 seconds.

view.SetReportingPeriod(5 * time.Second)

Traces

Starting and ending a span

ctx, span := trace.StartSpan(ctx, "your choice of name")
defer span.End()

More tracing examples are coming soon...

Profiles

OpenCensus tags can be applied as profiler labels for users who are on Go 1.9 and above.

ctx, err = tag.New(ctx,
	tag.Insert(osKey, "macOS-10.12.5"),
	tag.Insert(userIDKey, "fff0989878"),
)
if err != nil {
	log.Fatal(err)
}
tag.Do(ctx, func(ctx context.Context) {
	// Do work.
	// When profiling is on, samples will be
	// recorded with the key/values from the tag map.
})

A screenshot of the CPU profile from the program above: