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, "~> 0.5.0"},
{:opentelemetry_api, "~> 0.5.0"},
{:opentelemetry_honeycomb, "~> 0.5.0-rc.1"},

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_ATTRIBUTES=service.name=name,service.namespace=namespace

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

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

processors specifies otel_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 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",
}