OpenTelemetry

OpenTelemetry stats collection and distributed tracing framework for Erlang.

Requires OTP 21.3 or above.

Design

The OpenTelemetry specification defines a language library as having 2 components, the API and the SDK. The API must not only define the interfaces of any implementation in that language but also be able to function as a noop implementation of the tracer. The SDK is the default implementation of the API that must be optional.

When instrumenting a project your application should only depend on the OpenTelemetry API application, found in directory apps/opentelemetry_api of this repo which is published as the hex package opentelemetry_api.

This repository is the Erlang's SDK implementation and should be included in the final release and configured to setup the sampler, span processors and span exporters.

Usage

Hex Dependencies

It is recommended to use the versions published on hex.pm for OpenTelemetry API and OpenTelemetry SDK.

Git Dependencies

Because the OpenTelemetry OTP Applications are kept in a single repository, under the directory apps, either rebar3's git_subdir (rebar 3.14 or above is required) or mix's sparse feature must be used when using as Git dependencies in a project. The blocks below shows how in rebar3 and mix the git repo for the API and/or SDK Applications can be used.

{opentelemetry_api, {git_subdir,
"http://github.com/open-telemetry/opentelemetry-erlang", {branch, "main"}, "apps/opentelemetry_api"}}
{opentelemetry, {git_subdir,
"http://github.com/open-telemetry/opentelemetry-erlang", {branch, "main"}, "apps/opentelemetry"}}

{:opentelemetry_api, github: "open-telemetry/opentelemetry-erlang", sparse:
"apps/opentelemetry_api", override: true},
{:opentelemetry, github: "open-telemetry/opentelemetry-erlang", sparse: "apps/opentelemetry", override: true},

The override: true is required because the SDK Application, opentelemetry, has the API in its deps list of its rebar.config as a hex dependency and this will clash when mix tries to resolve the dependencies and fail without the override. override: true is also used on the SDK because the opentelemetry_exporter application depends on it and the API as hex deps so if it is included the override is necessary.

Including in Release

In an Erlang project add opentelemetry as the first element of the release's applications:

{relx, [{release, {<name>, <version>}, 
         [{opentelemetry, temporary},
          <your applications>]},
        ...]}.

In the above example opentelemetry is set to temporary so that if the opentelemetry application crashes, or is shutdown, it does not terminate the other applications in the project. This is optional, the opentelemetry application purposely sticks to permanent for the processes started by the root supervisor to leave it up to the end user whether they want the crash or shutdown or opentelemetry to be ignored or cause the shutdown of the rest of the applications in the release.

Doing the same for an Elixir project would be:

def project do
  [
    ...
    releases: [
      <name>: [
        applications: [opentelemetry: :temporary]
      ],

      ...
    ]
  ]
end

Benchmarks

Running benchmarks is done with benchee. Benchmark functions are in modules under samples/. To run them open a rebar3 shell in the bench profile:

$ rebar3 as bench compile

> otel_benchmarks:run().

If an Elixir script is wanted for the benchmarks they could be run like:

$ ERL_LIBS=_build/bench/lib/ mix run --no-mix-exs samples/run.exs

W3C Trace Context Interop Tests

Start the interop web server in a shell:

$ rebar3 as interop shell

> w3c_trace_context_interop:run().

Then, clone the W3C Trace Context repo and run the tests:

$ cd test
$ python3 test.py http://127.0.0.1:5000/test

Contributing

Approvers:

• Fred Hebert, Honeycomb

Maintainers:

• Łukasz Jan Niemier, Remote Technology, Inc.
• Ilya Khaprov, KOBIL Systems
• Tristan Sloughter