NewRelic.Tracer (New Relic Elixir Agent v1.27.8) View Source

Function Tracing

To enable function tracing in a particular module, use NewRelic.Tracer, and annotate the functions you want to @trace.

Traced functions will report as:

  • Segments in Transaction Traces
  • Span Events in Distributed Traces
  • Special custom attributes on Transaction Events


  • Traced functions will not be tail-call-recursive. Don't use this for recursive functions.


defmodule MyModule do
  use NewRelic.Tracer

  @trace :func
  def func do
    # Will report as `MyModule.func/0`


To categorize External Service calls you must give the trace annotation a category.

You may also call NewRelic.set_span to provide better naming for metrics & spans, and additonally annotate the outgoing HTTP headers with the Distributed Tracing context to track calls across services.

defmodule MyExternalService do
  use NewRelic.Tracer

  @trace {:request, category: :external}
  def request(method, url, headers) do
    NewRelic.set_span(:http, url: url, method: method, component: "HttpClient")
    headers ++ NewRelic.distributed_trace_headers(:http)
    HttpClient.request(method, url, headers)

This will:

  • Post External metrics to APM
  • Add custom attributes to Transaction events:
    • external_call_count
    • external_duration_ms
    • external.MyExternalService.query.call_count
    • external.MyExternalService.query.duration_ms

Transactions that call the traced ExternalService functions will contain external_call_count attribute

get "/endpoint" do
  ExternalService.request(:get, url, headers)
  send_resp(conn, 200, "ok")


By default, arguments are inspected and recorded along with traces. You can opt-out of function argument tracing on individual tracers:

defmodule SecretModule do
  use NewRelic.Tracer

  @trace {:login, args: false}
  def login(username, password) do
    # do something secret...

This will prevent the argument values from becoming part of Transaction Traces.

This may also be configured globally via Application config. See NewRelic.Config for details.