Ruby / Rack

Expose Prometheus metrics from any Ruby or Rack application — request rates, latencies, GC stats, and Puma thread pool — using the prometheus-client gem.

Pattern: Ruby prometheus-client → Prometheus scrape → xScaler remote_write

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Prerequisites

• Ruby 2.7+
• Puma or any Rack-compatible server
• xScaler tenant credentials (token + tenant ID)

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Option A — Prometheus Exporter

Add to Gemfile:

gem 'prometheus-client'
gem 'rack'

Mount the metrics endpoint in your Rack app (config.ru):

require 'prometheus/client'
require 'prometheus/client/rack/exporter'

registry = Prometheus::Client.registry

# Example counter
http_requests = registry.counter(:http_requests_total,
  docstring: 'Total HTTP requests',
  labels: [:method, :path, :status])

use Prometheus::Client::Rack::Exporter
# Track requests
use Prometheus::Client::Rack::Collector

run MyApp

Metrics are exposed at /metrics on your app port.

scrape_configs:
  - job_name: ruby_app
    static_configs:
      - targets: ['localhost:9292']

remote_write:
  - url: https://euw1-01.m.xscalerlabs.com/api/v1/push
    authorization:
      credentials: <token>
    headers:
      X-Scope-OrgID: <tenant-id>

---

Option B — Grafana Alloy

prometheus.scrape "ruby" {
  targets    = [{"__address__" = "localhost:9292"}]
  forward_to = [prometheus.remote_write.xscaler.receiver]
}

prometheus.remote_write "xscaler" {
  endpoint {
    url = "https://euw1-01.m.xscalerlabs.com/api/v1/push"
    authorization {
      type        = "Bearer"
      credentials = "<token>"
    }
    headers = { "X-Scope-OrgID" = "<tenant-id>" }
  }
}

---

Option C — OpenTelemetry Collector

Use the OpenTelemetry Ruby SDK with OTLP export instead:

# Gemfile
gem 'opentelemetry-sdk'
gem 'opentelemetry-exporter-otlp'
gem 'opentelemetry-instrumentation-rack'

# config/initializers/opentelemetry.rb
require 'opentelemetry/sdk'
require 'opentelemetry/exporter/otlp'

OpenTelemetry::SDK.configure do |c|
  c.use 'OpenTelemetry::Instrumentation::Rack'
end

Set env vars:

OTEL_EXPORTER_OTLP_ENDPOINT=https://euw1-01.m.xscalerlabs.com
OTEL_EXPORTER_OTLP_HEADERS="Authorization=Bearer <token>,X-Scope-OrgID=<tenant-id>"

---

Logs

Collect application log — tail the Rails or app log file with Alloy. Add the following to your Alloy config, adjusting __path__ to match your application's log file location:

local.file_match "ruby_logs" {
  path_targets = [{
    __address__ = "localhost",
    __path__    = "/var/log/ruby/app.log",
    instance    = constants.hostname,
    job         = "integrations/ruby",
  }]
}

loki.source.file "ruby_logs" {
  targets    = local.file_match.ruby_logs.targets
  forward_to = [loki.write.xscaler.receiver]
}

loki.write "xscaler" {
  endpoint {
    url = "https://euw1-01.l.xscalerlabs.com/api/v1/logs/push"

    http_client_config {
      authorization {
        type        = "Bearer"
        credentials = env("XSCALER_TOKEN")
      }
    }

    headers = { "X-Scope-OrgID" = env("XSCALER_TENANT_ID") }
  }
}

Key metrics

Metric	Description
http_requests_total	Total HTTP requests by method/path/status
http_request_duration_seconds	Request duration histogram
ruby_gc_runs_total	Ruby GC runs
ruby_process_cpu_seconds_total	Process CPU time
ruby_process_resident_memory_bytes	Process RSS memory
puma_backlog_total	Puma request backlog
puma_pool_capacity	Available Puma threads