Setting Up APM with C++

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Overview

This guide expands on the C++ APM docs to provide step-by-step instructions on how to set up a simple C++ app with APM on your VM for troubleshooting.

Setting up your box

Basic environment

First, spin up a fresh ubuntu/jammy64 Vagrant box and ssh into it with:

vagrant init ubuntu/jammy64
vagrant up
vagrant ssh

Next, install the agent with the instructions in the UI.

Prepping for C++

Install g++ and cmake with:

sudo apt-get update
sudo apt-get -y install g++ cmake

Download and install dd-trace-cpp library with:

wget https://github.com/DataDog/dd-trace-cpp/archive/v0.2.0.tar.gz -O dd-trace-cpp.tar.gz

If you get a rate limited message from GitHub, wait a few minutes and run the command again.

After downloading the tar file, unzip it:

tar zxvf dd-trace-cpp.tar.gz -C ./dd-trace-cpp/ --strip-components=1

Finally, build and install the library:

cd dd-trace-cpp
cmake -B build .
cmake --build build -j
cmake --install build

Building a simple app

Create a new file called tracer_example.cpp and populate it with the below code:

#include <datadog/tracer.h>
#include <iostream>
#include <string>

int main(int argc, char* argv[]) {
  datadog::tracing::TracerConfig tracer_config;
  tracer_config.service = "compiled-in example";

  const auto validated_config = dd::finalize_config(tracer_options);
  if (!validated_config) {
    std::cerr << validated_config.error() << '\n';
    return 1;
  }

  dd::Tracer tracer{*validated_config};

  // Create some spans.
  {
    datadog::tracing::SpanConfig options;
    options.name = "A";
    options.tags.emplace("tag", "123");
    auto span_a = tracer.create_span(options);

    auto span_b = span_a.create_child();
    span_b.set_name("B");
    span_b.set_tag("tag", "value");
  }

  return 0;
}

This creates a tracer that generates two spans, a parent span span_a and a child span span_b, and tags them.

Then, compile and link against libdd_trace_cpp with:

g++ -std=c++17 -o tracer_example tracer_example.cpp -ldd_trace_cpp

Finally, run the app with:

LD_LIBRARY_PATH=/usr/local/lib/ ./tracer_example

Sending traces

Now that an app exists, you can start sending traces and see the Trace Agent in action.

First, tail the Trace Agent log with:

tail -f /var/log/datadog/trace-agent.log

Next, open a new tab and run the example a couple times:

LD_LIBRARY_PATH=/usr/local/lib/ ./tracer_example

On the Trace Agent tab, you will see something similar to:

2019-08-09 20:02:26 UTC | TRACE | INFO | (pkg/trace/info/stats.go:108 in LogStats) | [lang:cpp lang_version:201402 tracer_version:0.2.0] -> traces received: 1, traces filtered: 0, traces amount: 363 bytes, events extracted: 0, events sampled: 0

The service then shows up in the Service Catalog in Datadog.