ocaml-opentelemetry/README.md

Opentelemetry

This project provides an API for instrumenting server software using opentelemetry, as well as connectors to talk to opentelemetry software such as jaeger.

• library opentelemetry should be used to instrument your code and possibly libraries. It doesn't communicate with anything except a backend (default: dummy backend);
• library opentelemetry-client-ocurl is a backend that communicates via http+protobuf with some collector (otelcol, datadog-agent, etc.) using cURL bindings;
• library opentelemetry-client-cohttp-lwt is a backend that communicates via http+protobuf with some collector using cohttp.

License

MIT

Features

• basic traces
• basic metrics
• basic logs
• nice API
• interface with lwt
• sync collector relying on ocurl
  • batching, perf, etc.
• async collector relying on ocurl-multi
• interface with logs (carry context around)
• implicit scope (via vendored ambient-context, see opentelemetry.ambient-context)

Use

For now, instrument traces/spans, logs, and metrics manually:

module Otel = Opentelemetry
let (let@) = (@@)

let foo () =
  let@ scope = Otel.Trace.with_  "foo"
      ~attrs:["hello", `String "world"] in
  do_work();
  Otel.Metrics.(
    emit [
      gauge ~name:"foo.x" [int 42];
    ]);
  do_more_work();
  ()

Setup

If you're writing a top-level application, you need to perform some initial configuration.

1. Set the service_name;
2. optionally configure [ambient-context][] with the appropriate storage for your environment — TLS, Lwt, Eio…;
3. and install a Collector (usually by calling your collector's with_setup function.)

For example, if your application is using Lwt, and you're using ocurl as your collector, you might do something like this:

let main () =
  Otel.Globals.service_name := "my_service";
  Otel.GC_metrics.basic_setup();

  Opentelemetry_ambient_context.set_storage_provider (Opentelemetry_ambient_context_lwt.storage ());
  Opentelemetry_client_ocurl.with_setup () @@ fun () ->
  (* … *)
  foo ();
  (* … *)

[ambient-context]: now vendored as opentelemetry.ambient-context, formerly https://v3.ocaml.org/p/ambient-context

Configuration

Environment Variables

The library supports standard OpenTelemetry environment variables:

General:

• OTEL_SDK_DISABLED - disable the SDK (default: false)
• OTEL_SERVICE_NAME - service name
• OTEL_RESOURCE_ATTRIBUTES - comma-separated key=value resource attributes
• OTEL_OCAML_DEBUG=1 - print debug messages from the opentelemetry library

Exporter endpoints:

• OTEL_EXPORTER_OTLP_ENDPOINT - base endpoint (default: http://localhost:4318)
• OTEL_EXPORTER_OTLP_TRACES_ENDPOINT - traces endpoint
• OTEL_EXPORTER_OTLP_METRICS_ENDPOINT - metrics endpoint
• OTEL_EXPORTER_OTLP_LOGS_ENDPOINT - logs endpoint

Exporter configuration:

• OTEL_EXPORTER_OTLP_PROTOCOL - protocol: http/protobuf or http/json (default: http/protobuf)

Headers:

• OTEL_EXPORTER_OTLP_HEADERS - headers as comma-separated key=value pairs
• OTEL_EXPORTER_OTLP_TRACES_HEADERS - traces-specific headers
• OTEL_EXPORTER_OTLP_METRICS_HEADERS - metrics-specific headers
• OTEL_EXPORTER_OTLP_LOGS_HEADERS - logs-specific headers

Collector opentelemetry-client-ocurl

This is a synchronous collector that uses the http+protobuf format to send signals (metrics, traces, logs) to some other collector (eg. otelcol or the datadog agent).

Do note that this backend uses a thread pool and is incompatible with uses of fork on some Unixy systems. See #68 for a possible workaround.

Collector opentelemetry-client-cohttp-lwt

This is a Lwt-friendly collector that uses cohttp to send signals to some other collector (e.g. otelcol). It must be run inside a Lwt_main.run scope.

Opentelemetry-trace

The optional library opentelemetry.trace, present if trace is installed, provides a collector for trace. This collector forwards and translates events from trace into opentelemetry. It's only useful if there also is also a OTEL collector.

License

MIT

Semantic Conventions

Not supported yet.

• metrics
• traces
• resources