# OTLP Exporter Example

This is an example of how to use the [OpenTelemetry
Protocol](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/README.md)
(OTLP) exporter.

The application in `grpc_main.cc` initializes an `OtlpGrpcExporter` instance,
the application in `http_main.cc` initializes an `OtlpHttpExporter` instance.
The application in `http_log_main.cc` initializes an `OtlpHttpLogExporter` instance,
the application in `grpc_log_main.cc` initializes an `OtlpGrpcLogExporter` instance.
And they register a tracer provider from the [OpenTelemetry
SDK](https://github.com/open-telemetry/opentelemetry-cpp). The application then
calls a `foo_library` which has been instrumented using the [OpenTelemetry
API](https://github.com/open-telemetry/opentelemetry-cpp/tree/main/api).

To enable TLS authentication for OTLP grpc exporter, SslCredentials can be used
by specifying the path to client certificate pem file, or the string containing
this certificate via OtlpGrpcExporterOptions. The path to such a .pem file can be
provided as a command-line argument alongwith the collector endpoint to the main
binary invocation above.

Resulting spans are exported to the **OpenTelemetry Collector** using the OTLP
exporter. The OpenTelemetry Collector can be configured to export to other
backends (see list of [supported
backends](https://github.com/open-telemetry/opentelemetry-collector/blob/main/exporter/README.md)).

Follow below command to run the **OpenTelemetry Collector** with OTLP receiver
in docker which dumps the received data into console. See [Getting
Started](https://opentelemetry.io/docs/collector/about/) for more information.

Open a terminal window at the root directory of this repo and launch the
OpenTelemetry Collector with an OTLP receiver by running:

- On Unix based systems use:

```console
docker run --rm -it -p 4317:4317 -p 4318:4318 -v $(pwd)/examples/otlp:/cfg otel/opentelemetry-collector:0.38.0 --config=/cfg/opentelemetry-collector-config/config.dev.yaml
```

- On Windows use:

```console
docker run --rm -it -p 4317:4317 -p 4318:4318 -v "%cd%/examples/otlp":/cfg otel/opentelemetry-collector:0.38.0 --config=/cfg/opentelemetry-collector-config/config.dev.yaml
```

Note that the OTLP gRPC and HTTP exporters connects to the Collector at `localhost:4317` and `localhost:4318/v1/traces` respectively. This can be changed with first argument from command-line, for example:
`./example_otlp_grpc gateway.docker.internal:4317` and
`./example_otlp_http gateway.docker.internal:4318/v1/traces`.

Once you have the Collector running, see
[CONTRIBUTING.md](../../CONTRIBUTING.md) for instructions on building and
running the example.

## Additional notes regarding Abseil library

gRPC internally uses a different version of Abseil than OpenTelemetry C++ SDK.

One option to optimize your code is to build the SDK with system-provided
Abseil library. If you are using CMake, then `-DWITH_ABSEIL=ON` may be passed
during the build of SDK to reuse the same Abseil library as gRPC. If you are
using Bazel, then `--@io_opentelemetry_cpp/api:with_abseil=true` may be passed
to reuse your Abseil library in your project.

If you do not want to pursue the above option, and in case if you run into
conflict between Abseil library and OpenTelemetry C++ `absl::variant`
implementation, please include either `grpcpp/grpcpp.h` or
`opentelemetry/exporters/otlp/otlp_grpc_exporter.h` BEFORE any other API
headers. This approach efficiently avoids the conflict between the two different
versions of Abseil.