OpenTelemetry.Honeycomb

opentelemetry_honeycomb provides an in-process OpenTelemetry exporter for Honeycomb.

Installation

Add opentelemetry, opentelemetry_api, and opentelemetry_honeycomb to your deps in mix.exs:

{:opentelemetry, "~> 0.4.0"},
{:opentelemetry_api, "~> 0.3.1"},
{:opentelemetry_honeycomb, "~> 0.3.0-rc.0"},

If you're using the default back ends, you'll also need hackney and poison:

{:hackney, ">= 1.11.0"},
{:poison, ">= 1.5.0"},

Configuration

A compact config/config.exs for opentelemetry_honeycomb is:

use Config

# You can also supply opentelemetry resources using environment variables, eg.:
# OTEL_RESOURCE_LABELS=service.name=name,service.namespace=namespace

config :opentelemetry, :resource,
  service: [
    name: "service-name",
    namespace: "service-namespace"
]

config :opentelemetry,
  processors: [
    ot_batch_processor: %{
    exporter:
      {OpenTelemetry.Honeycomb.Exporter, write_key: System.get_env("HONEYCOMB_WRITEKEY")}
    }
]

processors specifies ot_batch_processor, which specifies exporter, a 2-tuple of the exporter's module name and options to be supplied to its init/1. Our exporter takes a list of t:OpenTelemetry.Honeycomb.Config.config_opt/0 as its options.

Attribute Handling

OpenTelemetry supports a flat map of attribute keys to string, number, and boolean values (see t.OpenTelemetry.attribute_value/0). The API does not enforce this, implicitly supporting other attribute value types eg. maps until export time.

Honeycomb expects a flat JSON-serialisable object, but can be configured to flatten maps and stringify arrays at import time.

The data models being quite similar, we:

• Pass string, number, and boolean values through unmodified
• Flatten map values as described below
• Convert most other values to strings using inspect/1 with a short limit
• Trim string values longer than 49127 bytes

When trimming strings, we replace the last 3-7 characters of the trimmed string or so with an ellipsis ("...") of equal length. We choose the length of the ellipsis to avoid ending the trimmed string with a high-bit character, eg. splitting a UTF-8 code point.

We drop:

• Entire attribute lists that don't start as a list or map
• Entire list members that don't resemble key/value pairs

When flattening maps, we use periods (.) to delimit keys, for example this input:

%{
  http: %{
    host:  "localhost",
    method: "POST",
    path: "/api"
  }
}

... to this output:

%{
  "http.host" => "localhost",
  "http.method" => "POST",
  "http.path" => "/api",
}

Verification

First, we need to check :opentelemetry and :opentelemetry_api. Fire up iex -S mix and paste in the following code to install the :ot_exporter_stdout exporter:

:ot_batch_processor.set_exporter(:ot_exporter_stdout, [])

After a delay, you should see:

*SPANS FOR DEBUG*
*SPANS FOR DEBUG*
*SPANS FOR DEBUG*

Now, paste in some trace-sending code:

require OpenTelemetry.Tracer
require OpenTelemetry.Span

OpenTelemetry.Tracer.start_span("some-span")
OpenTelemetry.Tracer.current_span_ctx()
OpenTelemetry.Span.set_attributes(%{b: %{c: 2}})
OpenTelemetry.Tracer.end_span()

You should get output resembling:

{span,243384816483509084844220162257481913277,10418680972954126737,undefined,
      undefined,<<"some-span">>,'SPAN_KIND_UNSPECIFIED',-576460736343282000,
      -576460736342566000,
      #{b => #{c => 2}},
      [],[],undefined,undefined,1,true,undefined}

Next, we need to check OpenTelemetry.Honeycomb.Exporter. Paste in:

# hard way
:ot_batch_processor.set_exporter(OpenTelemetry.Honeycomb.Exporter,
  http_module: OpenTelemetry.Honeycomb.Http.ConsoleBackend,
  write_key: "HONEYCOMB_WRITEKEY"
)

# easy way
OpenTelemetry.Honeycomb.Http.ConsoleBackend.activate()

Paste in the trace-sending code again to see what the OpenTelemetry Honeycomb Exporter would have sent to Honeycomb:

POST /1/batch/opentelemetry HTTP/1.1
Host: api.honeycomb.io
Content-Type: application/json
User-Agent: opentelemetry_honeycomb/0.3.0-rc.0
X-Honeycomb-Team: HONEYCOMB_WRITEKEY

[
  {
    "time": "2020-04-24T06:12:16.698425Z",
    "samplerate": 1,
    "data": {
      "trace.trace_id": "6c14288156831d40602dc1f5a61489c0",
      "trace.span_id": "377fce3346b92811",
      "trace.parent_id": null,
      "service.namespace": "service-namespace",
      "service.name": "service-name",
      "name": "some-span",
      "duration_ms": 6.06005859375,
      "b.c": 2
    }
  }
]

Restore your configured exporter by pasting:

OpenTelemetry.Honeycomb.Http.ConsoleBackend.deactivate()

Development

Dependency management:

• mix deps.get to get your dependencies
• mix deps.compile to compile them
• mix licenses to check their license declarations, recursively

Finding problems:

• mix compile to compile your code
• mix credo to suggest more idiomatic style for it
• mix dialyzer to find problems static typing might spot... slowly
• mix test to run unit tests
• mix test.watch to run the tests again whenever you change something
• mix coveralls to check test coverage

Documentation:

• mix docs to generate documentation for this project
• mix help to find out what else you can do with mix

Changes since Opencensus.Honeycomb

• Removed decorator: use resources or extra processors.