Find file History
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Type Name Latest commit message Commit time
Failed to load latest commit information.


Stackdriver Debugger lets you inspect the state of a running application at any code location in real time, without stopping or slowing down the application, and without modifying the code to add logging statements. You can use Stackdriver Debugger with any deployment of your application, including test, development, and production. The Ruby debugger adds minimal request latency, typically less than 50ms, and only when application state is captured. In most cases, this is not noticeable by users.

Quick Start

Installing the gem

Add the google-cloud-debugger gem to your Gemfile:

gem "google-cloud-debugger"

Alternatively, consider installing the stackdriver gem. It includes the google-cloud-debugger gem as a dependency, and automatically initializes it for some application frameworks.

Initializing the Debugger

The Stackdriver Debugger library provides a Debugger agent that helps create breakpoints in your running applications. It then collects application snapshot data and transmits it to the Stackdriver Debugger service for you to view on the Google Cloud Console. The library also comes with a Railtie and a Rack Middleware to help control the Debugger agent in popular Rack based frameworks, such as Ruby on Rails and Sinatra.

Setup with Ruby on Rails

You can load the Railtie that comes with the library into your Ruby on Rails application by explicitly requiring it during the application startup:

# In config/application.rb
require "google/cloud/debugger/rails"

If you're using the stackdriver gem, it automatically loads the Railtie into your application when it starts.

Setup with other Rack-based frameworks

Other Rack-based frameworks, such as Sinatra, can use the Rack Middleware provided by the library:

require "google/cloud/debugger"
use Google::Cloud::Debugger::Middleware

Setup without a Rack-based framework

Non-rack-based applications can start the agent explicitly during the initialization code:

require "google/cloud/debugger"

Connecting to the Debugger

You can set breakpoints and view snapshots using the Google Cloud Console. If your app is hosted on Google Cloud (such as on Google App Engine, Google Kubernetes Engine, or Google Compute Engine), you can use the same project. Otherwise, if your application is hosted elsewhere, create a new project on Google Cloud.

Make sure the Stackdriver Debugger API is enabled on your Google Cloud project.

To connect to the Stackdriver Debugger service, the agent needs to be authenticated. If your application is hosted on Google Cloud Platform, much of this is handled for you automatically.

Connecting from Google App Engine (GAE)

If your app is running on Google App Engine, the Stackdriver Debugger agent authenticates automatically by default, and no additional configuration is required.

Connecting from Google Kubernetes Engine (GKE)

If your app is running on Google Kubernetes Engine, you must explicitly add the cloud_debugger OAuth scope when creating the cluster:

$ gcloud container clusters create example-cluster-name --scopes

You can also do this through the Google Cloud Platform Console. Select Enabled in the Cloud Platform section of Create a container cluster.

After the OAuth scope is enabled, the Stackdriver Debugger agent authenticates automatically by default, and no additional configuration is required.

Connecting from Google Compute Engine (GCE)

If your app is running on Google Compute Engine, its VM instances should have one of the following access scopes. These are only relevant when you use Compute Engine's default service account:


The cloud-platform access scope can be supplied when creating a new instance through the Google Cloud Platform Console. Select Allow full access to all Cloud APIs in the Identity and API access section of Create an instance.

The cloud_debugger access scope can be supplied manually using the SDK's gcloud compute instances create command or the gcloud compute instances set-service-account command.

After the OAuth scope is enabled, the Stackdriver Debugger agent authenticates automatically by default using the VM's service account, and no additional configuration is required.

Connecting from other hosting environments

To run the Stackdriver Debugger agent outside of Google Cloud Platform, you must supply your GCP project ID and appropriate service account credentials directly to the Stackdriver Debugger agent. This applies to running the agent on your own workstation, on your datacenter's computers, or on the VM instances of another cloud provider.

The best way to provide authentication information if you're using Ruby on Rails is through the Rails configuration interface:

# in config/environments/*.rb
Rails.application.configure do |config|
  # Shared parameters
  config.google_cloud.project_id = "your-project-id"
  config.google_cloud.credentials = "/path/to/key.json"
  # Or Stackdriver Debugger agent specific parameters
  config.google_cloud.debugger.project_id = "your-project-id"
  config.google_cloud.debugger.credentials = "/path/to/key.json"

Other Rack-based applications that are loading the Rack Middleware directly can use the configration interface:

require "google/cloud/debugger"
Google::Cloud.configure do |config|
  # Shared parameters
  config.project_id = "your-project-id"
  config.credentials = "/path/to/key.json"
  # Or Stackdriver Debugger agent specific parameters
  config.debugger.project_id = "your-project-id"
  config.debugger.credentials = "/path/to/key.json"

Or provide the parameters to the Stackdriver Debugger agent when it starts:

require "google/cloud/debugger" "your-project-id",
                            credentials: "/path/to/key.json").start

This library also supports the other authentication methods provided by the google-cloud-ruby suite. Instructions and configuration options are covered in the Authentication Guide.

Using the Debugger

When you set a breakpoint in the Stackdriver Debugger console, the agent takes a snapshot of application data when the breakpoint is hit. The application then continues running with minimal slowdown, and you can view the snapshot offline in the console.

By default, the snapshot includes the local variables from the current and four most recent stack frames. You may include additional data in the snapshot by providing a list of expressions when you create the breakpoint. Expressions may be instance variables, global variables, or the result of calling Ruby methods, or indeed, any Ruby expression.

For more information on using the debugger features, see the Stackdriver Debugger Documentation.

Working with Mutation Protection

To reduce the risk of corrupting your application data or changing your application's behavior, the debugger agent checks all expressions you provide for possible side effects before it runs them. If an expression calls any code that could modify the program state, by changing an instance variable for example, it is not evaluated.

This check is rather conservative, so if you are receiving mutation errors on an expression you know to be safe, you may disable the check by wrapping your expression in a call to Google::Cloud::Debugger.allow_mutating_methods!. For example:

Google::Cloud::Debugger.allow_mutating_methods! { my_expression() }

You may disable side effect checks globally by setting the allow_mutating_methods configuration. See the next section on configuring the agent.

Configuring the agent

You can customize the behavior of the Stackdriver Debugger agent. This includes setting the Google Cloud project and authentication, and customizing the behavior of the debugger itself, such as side effect protection and data size limits. See agent configuration for a list of possible configuration options.

Enabling Logging

To enable logging for this library, set the logger for the underlying gRPC library. The logger that you set may be a Ruby stdlib Logger as shown below, or a Google::Cloud::Logging::Logger that will write logs to Stackdriver Logging. See grpc/logconfig.rb and the gRPC spec_helper.rb for additional information.

Configuring a Ruby stdlib logger:

require "logger"

module MyLogger
  LOGGER = $stderr, level: Logger::WARN
  def logger

# Define a gRPC module-level logger method before grpc/logconfig.rb loads.
module GRPC
  extend MyLogger

Supported Ruby Versions

This library is supported on Ruby 2.3+.

Google provides official support for Ruby versions that are actively supported by Ruby Core—that is, Ruby versions that are either in normal maintenance or in security maintenance, and not end of life. Currently, this means Ruby 2.3 and later. Older versions of Ruby may still work, but are unsupported and not recommended. See for details about the Ruby support schedule.

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.


Please report bugs at the project on Github. Don't hesitate to ask questions about the client or APIs on StackOverflow.