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add opencensus bridge example
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dashpole committed Nov 19, 2020
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10 changes: 10 additions & 0 deletions .github/dependabot.yml
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Expand Up @@ -46,6 +46,16 @@ updates:
schedule:
day: sunday
interval: weekly
-
package-ecosystem: gomod
directory: /bridge/opencensus/examples/bridge
labels:
- dependencies
- go
- "Skip Changelog"
schedule:
day: sunday
interval: weekly
-
package-ecosystem: gomod
directory: /example/basic
Expand Down
70 changes: 70 additions & 0 deletions bridge/opencensus/README.md
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# OpenCensus Bridge

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

## The Problem: Mixing OpenCensus and OpenTelemetry libraries

In a perfect world, one would simply migrate their entire go application --including cusotom 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:

```golang
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 higherarchy.

### User Journey

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

To override OpenCensus' DefaultTracer with the bridge:
```golang
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)
```

### Incompatibilities

OpenCensus and OpenTelemetry APIs are not entirely compatible. If the bridge finds any incompatibilities, it will log them. Incompabitilities 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.
18 changes: 18 additions & 0 deletions bridge/opencensus/examples/bridge/go.mod
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module go.opentelemetry.io/otel/bridge/opencensus/examples/simple

go 1.14

replace (
go.opentelemetry.io/otel => ../../../..
go.opentelemetry.io/otel/bridge/opencensus => ../..
go.opentelemetry.io/otel/exporters/stdout => ../../../../exporters/stdout
go.opentelemetry.io/otel/sdk => ../../../../sdk
)

require (
go.opencensus.io v0.22.6-0.20201102222123-380f4078db9f
go.opentelemetry.io/otel v0.13.0
go.opentelemetry.io/otel/bridge/opencensus v0.0.0-20201117180221-c857a3da18cb
go.opentelemetry.io/otel/exporters/stdout v0.13.0
go.opentelemetry.io/otel/sdk v0.13.0
)
65 changes: 65 additions & 0 deletions bridge/opencensus/examples/bridge/go.sum
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58 changes: 58 additions & 0 deletions bridge/opencensus/examples/bridge/main.go
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// Copyright The OpenTelemetry Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package main // import "go.opentelemetry.io/otel/bridge/opencensus/examples/simple"

import (
"context"
"log"

octrace "go.opencensus.io/trace"

"go.opentelemetry.io/otel"
"go.opentelemetry.io/otel/bridge/opencensus"
"go.opentelemetry.io/otel/exporters/stdout"
sdktrace "go.opentelemetry.io/otel/sdk/trace"
)

func main() {
ctx := context.Background()

log.Println("Configuring opencensus. Not Registering any opencensus exporters.")
octrace.ApplyConfig(octrace.Config{DefaultSampler: octrace.AlwaysSample()})

log.Println("Registering opentelemetry stdout exporter.")
otExporter, err := stdout.NewExporter(stdout.WithPrettyPrint())
if err != nil {
log.Fatal(err)
}
tp := sdktrace.NewTracerProvider(sdktrace.WithSyncer(otExporter))
otel.SetTracerProvider(tp)

log.Println("Installing the OpenCensus bridge to make OpenCensus libraries write spans using OpenTelemetry.")
tracer := tp.Tracer("simple")
octrace.DefaultTracer = opencensus.NewTracer(tracer)

log.Println("Creating opencensus span, which should be printed out using the OpenTelemetry stdout exporter.\n-- It should have no parent, since it is the first span.")
ctx, outerOCSpan := octrace.StartSpan(ctx, "OpenCensusOuterSpan")
outerOCSpan.End()

log.Println("Creating opentelemetry span\n-- It should have the OC span as a parent, since the OC span was written with using OpenTelemetry APIs.")
ctx, otspan := tracer.Start(ctx, "OpenTelemetrySpan")
otspan.End()

log.Println("Creating opencensus span, which should be printed out using the OpenTelemetry stdout exporter.\n-- It should have the OTel span as a parent, since it was written using OpenTelemetry APIs")
_, innerOCSpan := octrace.StartSpan(ctx, "OpenCensusInnerSpan")
innerOCSpan.End()
}
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