feat: add experimental otlp metrics exporter

[xuan-cao-swi]

Description

Added otlp metrics exporter that works with otlp collector through http protocol.

Most code copied from (trace) exporter (with test as well) with the assumption of same ssl, http etc. configuration. The major change is the proto decode. If the log exporter also use the similar configuration, having a utility file can help DRY.

Quick demo

require 'opentelemetry/sdk'
require 'opentelemetry-metrics-sdk' # need to install this from building the metrics_sdk and metrics_api folder
require 'opentelemetry/exporter/otlp'

OpenTelemetry::SDK.configure

otlp_metric_exporter = OpenTelemetry::Exporter::OTLP::MetricsExporter.new

OpenTelemetry.meter_provider.add_metric_reader(otlp_metric_exporter)

meter = OpenTelemetry.meter_provider.meter("SAMPLE_METER_NAME")

histogram = meter.create_histogram('histogram', unit: 'smidgen', description: 'desscription')

histogram.record(123, attributes: {'foo' => 'bar'})

OpenTelemetry.meter_provider.metric_readers.each(&:pull)
OpenTelemetry.meter_provider.shutdown

Testing failed but it will success once the #1532 is merged.

[kaylareopelle]

Hi @xuan-cao-swi! Awesome progress on this! Thanks for putting it together. I’m still testing some of the functionality and may have other feedback soon.



In the meantime, I have a structural concern I'd like to discuss with you and the other reviewers.

It seems like the opentelemetry-ruby project prefers to put experimental code into separate gems, like with metrics_api and metrics_sdk. With that in mind, I put the draft OTLP logs exporter in a separate gem.

My suggestion is to move the OTLP metrics exporter to a separate gem to keep experimental code separate from the code folks use in their production environments.

However, this is my current opinion, and the maintainers/approvers may have something else in mind.
I hope this starts a discussion about the right path to take that can also apply to logs.

As you mentioned in the PR description, there's a ton of duplication in the logs OTLP exporter code. Eventually, I believe we will want to do a lot to DRY things up between the three signals, but at the moment, my gut tells me to keep signal exporters separate until they are stable.

[xuan-cao-swi]

Hi @kaylareopelle, thanks for the suggestions, I totally agree that experimental code in separate gem, and combine them in the future if needed. I will create another PR.

[xuan-cao-swi]

Closed, follow-up pr in #1551