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mirror of https://github.com/open-telemetry/opentelemetry-go.git synced 2024-12-14 10:13:10 +02:00
opentelemetry-go/bridge/opencensus
José Carlos Chávez 099df58e4e
chore: adds vanity import check. (#2255)
* chore: adds vanity import check.

* chore: runs vanity import check on ci.

* fix: set right target on CI.

* fix: fixes install for porto.

* fix: install right proto bin.

* chore: list all files insides the tools directory.

* fix: fixes vanity import target

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* chore(vanity-imports): adds vanity import support.

* fix: fixes internal generation.

* chore: runs go mod tidy in tools.

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>
Co-authored-by: Anthony Mirabella <a9@aneurysm9.com>
2021-09-27 22:37:26 -04:00
..
internal Update trace API config creation functions (#2212) 2021-09-01 15:44:13 -04:00
test Separate InstrumentationLibrary from metric.Descriptor (#2197) 2021-09-27 08:51:47 -07:00
aggregation_test.go OpenCensus metric exporter bridge (#1444) 2021-03-11 09:49:20 -08:00
aggregation.go chore: adds vanity import check. (#2255) 2021-09-27 22:37:26 -04:00
bridge.go chore: adds vanity import check. (#2255) 2021-09-27 22:37:26 -04:00
doc.go Update OpenCensus bridge docs with limitations (#2145) 2021-07-29 11:24:52 -07:00
exporter_test.go Separate InstrumentationLibrary from metric.Descriptor (#2197) 2021-09-27 08:51:47 -07:00
exporter.go chore: adds vanity import check. (#2255) 2021-09-27 22:37:26 -04:00
go.mod Separate InstrumentationLibrary from metric.Descriptor (#2197) 2021-09-27 08:51:47 -07:00
go.sum Separate InstrumentationLibrary from metric.Descriptor (#2197) 2021-09-27 08:51:47 -07:00
README.md Refactor exporter creation functions (#1985) 2021-06-10 09:22:47 -07:00

OpenCensus Bridge

The OpenCensus Bridge helps facilitate the migration of an application from OpenCensus to OpenTelemetry.

Caveat about OpenCensus

Installing a metric or tracing bridge will cause OpenCensus telemetry to be exported by OpenTelemetry exporters. Since OpenCensus telemetry uses globals, installing a bridge will result in telemetry collection from all libraries that use OpenCensus, including some you may not expect. For example (#1928), if a client library generates traces with OpenCensus, installing the bridge will cause those traces to be exported by OpenTelemetry.

Tracing

The Problem: Mixing OpenCensus and OpenTelemetry libraries

In a perfect world, one would simply migrate their entire go application --including custom instrumentation, libraries, and exporters-- from OpenCensus to OpenTelemetry all at once. In the real world, dependency constraints, third-party ownership of libraries, or other reasons may require mixing OpenCensus and OpenTelemetry libraries in a single application.

However, if you create the following spans in a go application:

ctx, ocSpan := opencensus.StartSpan(context.Background(), "OuterSpan")
defer ocSpan.End()
ctx, otSpan := opentelemetryTracer.Start(ctx, "MiddleSpan")
defer otSpan.End()
ctx, ocSpan := opencensus.StartSpan(ctx, "InnerSpan")
defer ocSpan.End()

OpenCensus reports (to OpenCensus exporters):

[--------OuterSpan------------]
    [----InnerSpan------]

OpenTelemetry reports (to OpenTelemetry exporters):

   [-----MiddleSpan--------]

Instead, I would prefer (to a single set of exporters):

[--------OuterSpan------------]
   [-----MiddleSpan--------]
    [----InnerSpan------]

The bridge solution

The bridge implements the OpenCensus trace API using OpenTelemetry. This would cause, for example, a span recorded with OpenCensus' StartSpan() method to be equivalent to recording a span using OpenTelemetry's tracer.Start() method. Funneling all tracing API calls to OpenTelemetry APIs results in the desired unified span hierarchy.

User Journey

Starting from an application using entirely OpenCensus APIs:

  1. Instantiate OpenTelemetry SDK and Exporters
  2. Override OpenCensus' DefaultTracer with the bridge
  3. Migrate libraries individually from OpenCensus to OpenTelemetry
  4. Remove OpenCensus exporters and configuration

To override OpenCensus' DefaultTracer with the bridge:

import (
	octrace "go.opencensus.io/trace"
	"go.opentelemetry.io/otel/bridge/opencensus"
	"go.opentelemetry.io/otel"
)

tracer := otel.GetTracerProvider().Tracer("bridge")
octrace.DefaultTracer = opencensus.NewTracer(tracer)

Be sure to set the Tracer name to your instrumentation package name instead of "bridge".

Incompatibilities

OpenCensus and OpenTelemetry APIs are not entirely compatible. If the bridge finds any incompatibilities, it will log them. Incompatibilities include:

  • Custom OpenCensus Samplers specified during StartSpan are ignored.
  • Links cannot be added to OpenCensus spans.
  • OpenTelemetry Debug or Deferred trace flags are dropped after an OpenCensus span is created.

Metrics

The problem: mixing libraries without mixing pipelines

The problem for monitoring is simpler than the problem for tracing, since there are no context propagation issues to deal with. However, it still is difficult for users to migrate an entire applications' monitoring at once. It should be possible to send metrics generated by OpenCensus libraries to an OpenTelemetry pipeline so that migrating a metric does not require maintaining separate export pipelines for OpenCensus and OpenTelemetry.

The Exporter "wrapper" solution

The solution we use here is to allow wrapping an OpenTelemetry exporter such that it implements the OpenCensus exporter interfaces. This allows a single exporter to be used for metrics from both OpenCensus and OpenTelemetry.

User Journey

Starting from an application using entirely OpenCensus APIs:

  1. Instantiate OpenTelemetry SDK and Exporters.
  2. Replace OpenCensus exporters with a wrapped OpenTelemetry exporter from step 1.
  3. Migrate libraries individually from OpenCensus to OpenTelemetry
  4. Remove OpenCensus Exporters and configuration.

For example, to swap out the OpenCensus logging exporter for the OpenTelemetry stdout exporter:

import (
	"go.opencensus.io/metric/metricexport"
	"go.opentelemetry.io/otel/bridge/opencensus"
	"go.opentelemetry.io/otel/exporters/stdout"
	"go.opentelemetry.io/otel"
)
// With OpenCensus, you could have previously configured the logging exporter like this:
//       import logexporter "go.opencensus.io/examples/exporter"
//       exporter, _ := logexporter.NewLogExporter(logexporter.Options{})
// Instead, we can create an equivalent using the OpenTelemetry stdout exporter:
openTelemetryExporter, _ := stdout.New(stdout.WithPrettyPrint())
exporter := opencensus.NewMetricExporter(openTelemetryExporter)

// Use the wrapped OpenTelemetry exporter like you normally would with OpenCensus
intervalReader, _ := metricexport.NewIntervalReader(&metricexport.Reader{}, exporter)
intervalReader.Start()