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Repository: govuk_app_config

Gem to configure GOV.UK Ruby applications



Adds the basics of a GOV.UK application:

  • Unicorn as a web server
  • Error reporting with Sentry
  • Statsd client for reporting stats
  • Rails logging
  • Content Security Policy generation for frontend apps
  • Prometheus monitoring for EKS


Add this line to your application’s Gemfile:

gem "govuk_app_config"

And then execute:

$ bundle



Find or create a config/unicorn.rb in the app

At the start of the file insert:

require "govuk_app_config/govuk_unicorn"


To serve an app with unicorn run:

$ bundle exec unicorn -c config/unicorn.rb

Error reporting

Automatic error reporting

If you include govuk_app_config in your Gemfile, Rails’ autoloading mechanism will make sure that your application is configured to send errors to Sentry.

Your app will have to have the following environment variables set:

Manual error reporting

Report something to Sentry manually:

GovukError.notify("Something went terribly wrong")
GovukError.notify("Or some exception object"))

Extra parameters are:

  extra: { offending_content_id: "123" }, # Additional context for this event. Must be a hash. Children can be any native JSON type.
  level: "debug", # debug, info, warning, error, fatal
  tags: { key: "value" } # Tags to index with this event. Must be a mapping of strings.

Active Sentry environments

GovukError will only send errors to Sentry if your SENTRY_CURRENT_ENV matches one of the ‘active environments’ in the default configuration. This is to prevent temporary test environments from flooding our Sentry account with errors.

You can add your environment to the list of active Sentry environments like so:

GovukError.configure do |config|
  config.enabled_environments << "my-test-environment"

Error configuration

You can exclude certain errors from being reported using this:

GovukError.configure do |config|
  config.excluded_exceptions << "RetryableError"

And you can exclude errors from being reported if they occur during the nightly data sync (on integration and staging):

GovukError.configure do |config|
  config.data_sync_excluded_exceptions << "PG::Error"

Finally, you can pass your own callback to evaluate whether or not to capture the exception. Note that if an exception is on the excluded_exceptions list, or on the data_sync_excluded_exceptions and occurs at the time of a data sync, then it will be excluded even if the custom before_send callback doesn’t return nil.

GovukError.configure do |config|
  config.before_send = lambda do |event, hint|
    hint[:exception].is_a?(ErrorWeWantToIgnore) ? nil : event

GovukError.configure has the same options as the Sentry client, Raven. See the Raven docs for all configuration options.


Use GovukStatsd to send stats to graphite. It has the same interface as the Ruby Statsd client.


GovukStatsd.increment "garets"
GovukStatsd.timing "glork", 320
GovukStatsd.gauge "bork", 100

# Use {#time} to time the execution of a block
GovukStatsd.time("account.activate") { @account.activate! }

Health Checks

This Gem provides a common “health check” framework for apps. See the health check docs for more information on how to use it.

Rails logging

In Rails applications, the application will be configured to send JSON-formatted logs to STDOUT and unstructed logs to STDERR.

Content Security Policy generation

For frontend apps, configuration can be added to generate and serve a content security policy header. The policy is report only when the environment variable GOVUK_CSP_REPORT_ONLY is set, and enforced otherwise.

To enable this feature, create a file at config/initializers/csp.rb in the app with the following content:


i18n rules

Some frontend apps support languages that are not defined in the i18n gem. This provides them with our own custom rules for these languages.

Prometheus monitoring for EKS

Create a /config/initializers/prometheus.rb file in the app and add the following

require "govuk_app_config/govuk_prometheus_exporter" 


MIT License