OpenCensus - A stats collection and distributed tracing framework

This is the open-source release of Census for Ruby. Census provides a framework to measure a server's resource usage and collect performance stats.

This repository contains the source to the opencensus Rubygem, which contains the core OpenCensus APIs and basic integrations with Rails, Faraday, and GRPC. Additional integrations, including exporters to popular analytics services, will be available in separate gems.

The library is in alpha stage, and the API is subject to change. In particular, support for the Stats API is currently incomplete and experimental.

Quick Start


Install the gem directly:

$ gem install opencensus

Or install through Bundler:

  1. Add the opencensus gem to your Gemfile:
gem "opencensus"
  1. Use Bundler to install the gem:
$ bundle install

Getting started with Ruby on Rails

The OpenCensus library provides a Railtie that integrates with Ruby On Rails, automatically tracing incoming requests in the application. It also automatically traces key processes in your application such as database queries and view rendering.

To enable Rails integration, require this file during application startup:

# In config/application.rb
require "opencensus/trace/integrations/rails"

See the documentation for the Rails integration class for more information.

Getting started with other Rack-based frameworks

Other Rack-based frameworks, such as Sinatra, can use the Rack Middleware integration, which automatically traces incoming requests. To enable the integration for a non-Rails Rack framework, add the middleware to your middleware stack.

# In or similar Rack configuration file
require "opencensus/trace/integrations/rack_middleware"
use OpenCensus::Trace::Integrations::RackMiddleware

Instrumentation features

Tracing outgoing HTTP requests

If your app uses the Faraday library to make outgoing HTTP requests, consider installing the Faraday Middleware integration. This integration creates a span for each outgoing Faraday request, tracking the latency of that request, and propagates distributed trace headers into the request so you can potentially connect your request trace with that of the remote service. Here is an example:

require "opencensus/trace/integrations/rack_middleware"
conn = "") do |c|
  c.use OpenCensus::Trace::Integrations::FaradayMiddleware
  c.adapter Faraday.default_adapter
conn.get "/"

See the documentation for the FaradayMiddleware class for more info.

Adding Custom Trace Spans

In addition to the spans added by the Rails integration (e.g. for database queries) and by Faraday integration for outgoing HTTP requests, you can add additional custom spans to the request trace:

OpenCensus::Trace.in_span "my_task" do |span|
  # Do stuff...

  OpenCensus::Trace.in_span "my_subtask" do |subspan|
    # Do other stuff

See the documentation for the OpenCensus::Trace module for more info.

Exporting traces

By default, OpenCensus will log request trace data as JSON. To export traces to your favorite analytics backend, install an export plugin.

The provided exporters are:

Class Description
LoggerExporter Exporter JSON encoded spans to a standard Ruby Logger interface
StackdriverExporter Report traces to Google Cloud Stackdriver Trace
ZipkinExporter Report collected spans to a Zipkin server

You may also create your own Exporter

Configuring the library

OpenCensus allows configuration of a number of aspects via the configuration class. The following example illustrates how that looks:

OpenCensus.configure do |c|
  c.trace.default_sampler =
  c.trace.default_max_attributes = 16

If you are using Rails, you can equivalently use the Rails config:

config.opencensus.trace.default_sampler =
config.opencensus.trace.default_max_attributes = 16

You can configure a variety of core OpenCensus options, including:

  • Sampling, which controls how often a request is traced.
  • Exporting, which controls how trace information is reported.
  • Formatting, which controls how distributed request trace headers are constructed
  • Size maximums, which control when trace data is truncated.

Additionally, integrations and other plugins might have their own configurations.

For more information, consult the documentation for OpenCensus.configure and OpenCensus::Trace.configure.

About the library

Supported Ruby Versions

This library is supported on Ruby 2.2+.

However, Ruby 2.3 or later is strongly recommended, as earlier releases have reached or are nearing end-of-life. After June 1, 2018, OpenCensus will provide official support only for Ruby versions that are considered current and supported by Ruby Core (that is, Ruby versions that are either in normal maintenance or in security maintenance). See for further details.


This library follows Semantic Versioning.

It is currently in major version zero (0.y.z), which means that anything may change at any time, and the public API should not be considered stable.


Contributions to this library are always welcome and highly encouraged.

See the Contributing Guide for more information on how to get started.

Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms. See Code of Conduct for more information.


This library is licensed under Apache 2.0. Full license text is available in LICENSE.


This is not an official Google product.