# opentelemetry-exporter-otlp-metrics

The `opentelemetry-exporter-otlp-metrics` gem provides an [OTLP](https://github.com/open-telemetry/opentelemetry-proto) metrics exporter for OpenTelemetry for Ruby. Using `opentelemetry-exporter-otlp-metrics`, an application can configure OpenTelemetry to export collected metrics data to [the OpenTelemetry Collector][opentelemetry-collector-home].

## What is OpenTelemetry?

[OpenTelemetry][opentelemetry-home] is an open source observability framework, providing a general-purpose API, SDK, and related tools required for the instrumentation of cloud-native software, frameworks, and libraries.

OpenTelemetry provides a single set of APIs, libraries, agents, and collector services to capture distributed traces and metrics from your application. You can analyze them using Prometheus, Jaeger, and other observability tools.

## How does this gem fit in?

The `opentelemetry-exporter-otlp-metrics` gem is a plugin that provides OTLP export. To export to the OpenTelemetry Collector, an application can include this gem along with `opentelemetry-sdk`, and configure the `SDK` to use the provided OTLP exporter with a metric reader.

Generally, *libraries* that produce telemetry data should avoid depending directly on specific exporter, deferring that choice to the application developer.

### Supported protocol version

This gem supports the [v0.20.0 release][otel-proto-release] of OTLP.

## Prerequisite

The exporter-oltp-metrics depends on two gems that have not been officially released: opentelemetry-metrics-sdk and opentelemetry-metrics-api.

Within the .gemspec file, these gems are not listed as dependencies. However, for users who need utilize this metrics exporter, they must first install and load these two gems before they can use the exporter.

To facilitate this, there are couple recommended approaches:

### 1. Download the source code

1. Download the [opentelemetry-ruby](https://github.com/open-telemetry/opentelemetry-ruby).
2. Navigate to subfolder, then build the [metrics_sdk](https://github.com/open-telemetry/opentelemetry-ruby/tree/main/metrics_sdk) and [metrics_api](https://github.com/open-telemetry/opentelemetry-ruby/tree/main/metrics_api).
3. Execute `gem build *.gemspec`.
4. Lastly, install the built gem into the system.

### 2. Using `path:` option in Gemfile with downloaded source code

git clone [opentelemetry-ruby](https://github.com/open-telemetry/opentelemetry-ruby) first, then use Gemfile

```ruby
# Gemfile
source 'https://rubygems.org'
gem 'opentelemetry-metrics-api', path: "opentelemetry-ruby/metrics_api"
gem 'opentelemetry-metrics-sdk', path: "opentelemetry-ruby/metrics_sdk"
```

### 3. Using `git:` option in Gemfile

```ruby
# Gemfile
source 'https://rubygems.org'
gem 'opentelemetry-metrics-api', git: "https://github.com/open-telemetry/opentelemetry-ruby", glob: 'metrics_api/*.gemspec'
gem 'opentelemetry-metrics-sdk', git: "https://github.com/open-telemetry/opentelemetry-ruby", glob: 'metrics_sdk/*.gemspec'
```

## How do I get started?

Install the gem using:

```console

gem install opentelemetry-sdk
gem install opentelemetry-metrics-sdk
gem install opentelemetry-exporter-otlp-metrics

```

Or, if you use [bundler][bundler-home], include `opentelemetry-sdk`, `opentelemetry-metrics-sdk`, and `opentelemetry-exporter-otlp-metrics` in your `Gemfile`.

Then, configure the SDK to use the OTLP metrics exporter

```ruby
require 'opentelemetry/sdk'
require 'opentelemetry-metrics-sdk'
require 'opentelemetry/exporter/otlp_metrics'

OpenTelemetry::SDK.configure

# To start a trace you need to get a Tracer from the TracerProvider

otlp_metric_exporter = OpenTelemetry::Exporter::OTLP::Metrics::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
```

For additional examples, see the [examples on github][examples-github].

## How can I configure the OTLP metrics exporter?

The collector exporter can be configured explicitly in code, or via environment variables as shown above. The configuration parameters, environment variables, and defaults are shown below.

| Parameter           | Environment variable                         | Default                             |
| ------------------- | -------------------------------------------- | ----------------------------------- |
| `endpoint:`         | `OTEL_EXPORTER_OTLP_ENDPOINT`                | `"http://localhost:4318/v1/metrics"` |
| `certificate_file: `| `OTEL_EXPORTER_OTLP_CERTIFICATE`             |                                     |
| `client_certificate_file: `| `OTEL_EXPORTER_OTLP_CLIENT_CERTIFICATE` |                                   |
| `client_key_file:`       | `OTEL_EXPORTER_OTLP_CLIENT_KEY`              |                                     |
| `headers:`          | `OTEL_EXPORTER_OTLP_HEADERS`                 |                                     |
| `compression:`      | `OTEL_EXPORTER_OTLP_COMPRESSION`             | `"gzip"`                            |
| `timeout:`          | `OTEL_EXPORTER_OTLP_TIMEOUT`                 | `10`                                |
| `ssl_verify_mode:`  | `OTEL_RUBY_EXPORTER_OTLP_SSL_VERIFY_PEER` or `OTEL_RUBY_EXPORTER_OTLP_SSL_VERIFY_NONE` | `OpenSSL::SSL:VERIFY_PEER`          |

`ssl_verify_mode:` parameter values should be flags for server certificate verification: `OpenSSL::SSL:VERIFY_PEER` and `OpenSSL::SSL:VERIFY_NONE` are acceptable. These values can also be set using the appropriately named environment variables as shown where `VERIFY_PEER` will take precedence over `VERIFY_NONE`.  Please see [the Net::HTTP docs](https://ruby-doc.org/stdlib-2.7.6/libdoc/net/http/rdoc/Net/HTTP.html#verify_mode) for more information about these flags.

## How can I get involved?

The `opentelemetry-exporter-otlp-metrics` gem source is [on github][repo-github], along with related gems including `opentelemetry-metrics-sdk`.

The OpenTelemetry Ruby gems are maintained by the OpenTelemetry-Ruby special interest group (SIG). You can get involved by joining us in [GitHub Discussions][discussions-url] or attending our weekly meeting. See the [meeting calendar][community-meetings] for dates and times. For more information on this and other language SIGs, see the OpenTelemetry [community page][ruby-sig].

## License

The `opentelemetry-exporter-otlp-metrics` gem is distributed under the Apache 2.0 license. See [LICENSE][license-github] for more information.

## Working with Proto Definitions

The OTel community maintains a [repository with protobuf definitions][otel-proto-github] that language and collector implementers use to generate code.

Maintainers are expected to keep up to date with the latest version of protos. This guide will provide you with step-by-step instructions on updating the OTLP Exporter gem with the latest definitions.

### System Requirements

- [`git` 2.41+][git-install]
- [`protoc` 22.5][protoc-install]
- [Ruby 3+][ruby-downloads]

> :warning: `protoc 23.x` *changes the Ruby code generator to emit a serialized proto instead of a DSL.* <https://protobuf.dev/news/2023-04-20/>. Please ensure you use `protoc` version `22.x` in order to ensure we remain compatible with versions of protobuf prior to `google-protobuf` gem `3.18`.

### Upgrade Proto Definitions

**Update the target otel-proto version in the `Rakefile` that matches a release `tag` in the proto repo, e.g.**

```ruby
  # Rakefile

  # https://github.com/open-telemetry/opentelemetry-proto/tree/v0.20.0
  PROTO_VERSION = `v0.20.0`
```

**Generate the Ruby source files using `rake`:**

```console

$> bundle exec rake protobuf:generate

```

**Run tests and fix any errors:**

```console

$> bundle exec rake test

```

**Commit the changes and open a PR!**

[opentelemetry-collector-home]: https://opentelemetry.io/docs/collector/about/
[opentelemetry-home]: https://opentelemetry.io
[bundler-home]: https://bundler.io
[repo-github]: https://github.com/open-telemetry/opentelemetry-ruby
[license-github]: https://github.com/open-telemetry/opentelemetry-ruby/blob/main/LICENSE
[examples-github]: https://github.com/open-telemetry/opentelemetry-ruby/tree/main/examples
[ruby-sig]: https://github.com/open-telemetry/community#ruby-sig
[community-meetings]: https://github.com/open-telemetry/community#community-meetings
[discussions-url]: https://github.com/open-telemetry/opentelemetry-ruby/discussions
[git-install]: https://git-scm.com/book/en/v2/Getting-Started-Installing-Git
[protoc-install]: https://github.com/protocolbuffers/protobuf/releases/tag/v22.5
[ruby-downloads]: https://www.ruby-lang.org/en/downloads/
[otel-proto-github]: https://github.com/open-telemetry/opentelemetry-proto
[otel-proto-release]: https://github.com/open-telemetry/opentelemetry-proto/releases/tag/v0.20.0