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Monitoring Ruby Applications with Prometheus

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You can instrument your Ruby application with the official Prometheus Ruby client library and let the Glouton agent scrape its /metrics endpoint.

Install the client library

Section titled “Install the client library”
Terminal window
gem install prometheus-client

Or add it to your Gemfile:

gem "prometheus-client"

Minimal example

Section titled “Minimal example”

The snippet below defines a counter and exposes it on http://localhost:8080/metrics using the Rack middleware shipped with the client:

require "rack"
require "prometheus/client"
require "prometheus/middleware/exporter"


registry = Prometheus::Client.registry
requests_total = registry.counter(
  :myapp_requests_total,
  docstring: "Total number of processed requests.",
)


app = Rack::Builder.new do
  use Prometheus::Middleware::Exporter
  run ->(env) {
    requests_total.increment
    [200, { "Content-Type" => "text/plain" }, ["Hello"]]
  }
end


Rack::Handler::WEBrick.run(app, Port: 8080)

Scrape with Glouton

Section titled “Scrape with Glouton”

Configure Glouton to scrape your application by adding the following to /etc/glouton/conf.d/50-prometheus-metrics.conf:

metric:
  prometheus:
    targets:
      - url: "http://localhost:8080/metrics"
        name: "my_ruby_application"
        allow_metrics:
          - "myapp_requests_total"

Restart the agent to apply the configuration. See Prometheus Monitoring for the full list of options, including Docker label auto-discovery and Kubernetes annotations.

Learn more

Section titled “Learn more”