View Source Tesla.Middleware.Telemetry (tesla v1.13.2)

Emits events using the :telemetry library to expose instrumentation.

Examples

defmodule MyClient do
  def client do
    Tesla.client([Tesla.Middleware.Telemetry])
  end
end

:telemetry.attach(
  "my-tesla-telemetry",
  [:tesla, :request, :stop],
  fn event, measurements, meta, config ->
    # Do something with the event
  end,
  nil
)

Options

• :metadata - additional metadata passed to telemetry events

Telemetry Events

• [:tesla, :request, :start] - emitted at the beginning of the request.

  • Measurement: %{system_time: System.system_time()}
  • Metadata: %{env: Tesla.Env.t()}

• [:tesla, :request, :stop] - emitted at the end of the request.

  • Measurement: %{duration: native_time}

  • Metadata: %{env: Tesla.Env.t()} | %{env: Tesla.Env.t(), error: term()}

• [:tesla, :request, :exception] - emitted when an exception has been raised.

  • Measurement: %{duration: native_time}
  • Metadata: %{env: Tesla.Env.t(), kind: Exception.kind(), reason: term(), stacktrace: Exception.stacktrace()}

Legacy Telemetry Events

• [:tesla, :request] - This event is emitted for backwards compatibility only and should be considered deprecated. This event can be disabled by setting config :tesla, Tesla.Middleware.Telemetry, disable_legacy_event: true in your config. Be sure to run mix deps.compile --force tesla after changing this setting to ensure the change is picked up.

Please check the telemetry for further usage.

URL event scoping with Tesla.Middleware.PathParams and Tesla.Middleware.KeepRequest

Sometimes, it is useful to have access to a template URL (i.e. "/users/:user_id") for grouping Telemetry events. For such cases, a combination of the Tesla.Middleware.PathParams, Tesla.Middleware.Telemetry and Tesla.Middleware.KeepRequest may be used.

defmodule MyClient do
  def client do
    Tesla.client([
      # The KeepRequest middleware sets the template URL as a Tesla.Env.opts entry
      # Said entry must be used because on happy-path scenarios,
      # the Telemetry middleware will receive the Tesla.Env.url resolved by PathParams.
      Tesla.Middleware.KeepRequest,
      Tesla.Middleware.PathParams,
      Tesla.Middleware.Telemetry
    ])
  end
end

:telemetry.attach(
  "my-tesla-telemetry",
  [:tesla, :request, :stop],
  fn event, measurements, meta, config ->
    path_params_template_url = meta.env.opts[:req_url]
    # The meta.env.url key will only present the resolved URL on happy-path scenarios.
    # Error cases will still return the original template URL.
    path_params_resolved_url = meta.env.url
  end,
  nil
)

Order Matters

Place the Tesla.Middleware.Telemetry middleware as close as possible to the end of the middleware stack to ensure that you are measuring the actual request itself and do not lose any information about the Tesla.Env.t/0 due to some transformation that happens in the middleware stack before reaching the Tesla.Middleware.Telemetry middleware.