emit_telemetry_tag is a logging tag that when applied to a log, determines if a log will be emitted by the tracing/telemetry backend.

Since some OTel backends can cause deadlocks if used during a GC alarm, this is useful for when you may want logging during a GC alarm. It is also useful if you want to log sensitive information, but not report it via Opentelemetry.

If this tag is not set on a log, said log will be emitted by default if the otel reporter is registered.

Example:

  let tags =
    Logs.Tag.(add Opentelemetry_logs.emit_telemetry_tag false other_tags)
  in
  Logs.info (fun m ->
      m ~tags "This log will not be sent to the telemetry backend")

emit_telemetry emit_or_not creates a tag set with the emit_telemetry_tag as its only member

otel_reporter ?service_name ?tag_value_pp_buffer_size ?attrs () creates a Logs.reporter that will create and emit an OTel log with the following info:

• Log severity is converted to OTel severity as follows:

    module Otel = Opentelemetry
    match level with
    | Logs.App -> Otel.Logs.Severity_number_info (* like info, but less severe  *)
    | Logs.Info -> Otel.Logs.Severity_number_info2
    | Logs.Error -> Otel.Logs.Severity_number_error
    | Logs.Warning -> Otel.Logs.Severity_number_warn
    | Logs.Debug -> Otel.Logs.Severity_number_debug

• message is the formatted with the given fmt and msgf function, and emitted as the log body
• header and src will be added as attributes ("header", `String header) and ("src", `String (Logs.Src.name src)) respectively
• tags will be also added as attributes, with the tag name as the key, and the value formatted via its formatter as the value.
• attributes will also be added as attributes, and are useful for setting static attributes such as a library name

Example use: Logs.set_reporter (Opentelemetery_logs.otel_reporter ())

attach_otel_reporter ?service_name ?attributes reporter will create a reporter that first calls the reporter passed as an argument, then an otel report created via otel_reporter, for every log. This is useful for if you want to emit logs to stderr and to OTel at the same time.

Example:

  let reporter = Logs_fmt.reporter () in
  Logs.set_reporter
    (Opentelemetry_logs.attach_otel_reporter ?service_name ?attributes
       reporter)