opentelemetry-go/example/otel-collector/README.md

# OpenTelemetry Collector Traces Example

This example illustrates how to export traces from the OpenTelemetry-Go SDK to the OpenTelemetry Collector, and from there to a Jaeger instance.
The complete flow is:

`otel-collector-demo -> otel-collector -> Jaeger`

# Prerequisites

The demo assumes you already have both OpenTelemetry Collector and Jaeger up and running. For setting these up, please follow the corresponding documentations:
* Jaeger: https://www.jaegertracing.io/docs/1.17/getting-started/
* OpenTelemetry Collector: https://opentelemetry.io/docs/collector/about/

Moreover, this demo is build against a microk8s cluster running both the OpenTelemetry Collector, and Jaeger. Therefor, the OpenTelemetry Collector configuration illustrated is a K8S ConfigurationMap. But the gist of it is there, so it shouldn't matter too much.

# Configuring the OTEL Collector

In order to enable our application to send traces to the OpenTelemetry Collector, we need to first open up the OTLP receiver:

```yml
receivers:
      otlp: {}
```

This will create the receiver on the Collector side, and open up port `55680` for receiving traces.
The rest of the configuration is quite standard, with the only mention that we need to create the Jaeger exporter:
```yml
exporters:
      jaeger:
        # Replace with a real endpoint.
        endpoint: "<jaeger-service-url>:14250"
```

After this, apply the configuration to your OpenTelemetry Collector instance (with `k apply -f otel-controller-config.yaml` for k8s users). You should see that the Collector creates the otlp receiver:
```json
{"level":"info","ts":1589184143.206609,"caller":"builder/receivers_builder.go:79","msg":"Receiver started.","component_kind":"receiver","component_type":"otlp","component_name":"otlp"}
```
and the Jaeger exporter:
```json
{"level":"info","ts":1589184143.1535392,"caller":"builder/exporters_builder.go:94","msg":"Exporter started.","component_kind":"exporter","component_type":"jaeger","component_name":"jaeger"}
```

# Writing the demo

Having the OpenTelemetry Collector started with the OTLP port open for traces, and connected to Jaeger, let's look at the go app that will send traces to the Collector.

First, we need to create an exporter using the otlp package:
```go
exp, _ := otlp.NewExporter(otlp.WithInsecure(),
        // For debug purposes
        otlp.WithGRPCDialOption(grpc.WithBlock()))
defer func() {
		_ = exp.Stop()
	}()
```
This will initialize the exporter with the default configuration. In this configuration, it will try to connect to an otlp receiver at the address `localhost:55680`. If your OpenTelemetry Collector is running at a different address, use the [otlp.WithAddress](https://pkg.go.dev/go.opentelemetry.io/otel/exporters/otlp?tab=doc#WithAddress) function to change the default address.

Feel free to remove the blocking operation, but it might come in handy when testing the connection. Also, make sure to close the exporter before the app exits.

The next steps are the same as for all other otel-go sdk uses:
1) Create a trace provider from the `otlp` exporter: 
```go
tp, _ := sdktrace.NewProvider(
		sdktrace.WithConfig(sdktrace.Config{DefaultSampler: sdktrace.AlwaysSample()}),
		sdktrace.WithBatcher(exp, // add following two options to ensure flush
			sdktrace.WithScheduleDelayMillis(5),
			sdktrace.WithMaxExportBatchSize(2),
        ))
```

2) Start sending traces:
```go
tracer := tp.Tracer("test-tracer")
ctx, span := tracer.Start(context.Background(), "CollectorExporter-Example")
	defer span.End()
```

The traces should now be visible from the Jaeger UI (if you have it installed).

# Notes

* There is an issue with the exporter/Collector which causes Jaeger to throw errors when receiving spans from the OpenTelemetry Collector: https://github.com/open-telemetry/opentelemetry-collector/issues/815