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Repository: govuk_app_config

Gem to configure GOV.UK Ruby applications


Adds the basics of a GOV.UK application:

  • Puma as a web server
  • Error reporting with Sentry
  • Prometheus monitoring for EKS
  • Statsd client for reporting stats (deprecated; use Prometheus instead)
  • Rails logging
  • Content Security Policy generation for frontend apps


Add this line to your application’s Gemfile:

gem "govuk_app_config"

Then run bundle.



Create a file config/puma.rb in the app, containing:

require "govuk_app_config/govuk_puma"


To run an app locally with Puma, run: bundle exec puma or bundle exec rails s.

Error reporting

Automatic error reporting

If you include govuk_app_config in your Gemfile and set the following environment variables, your application will automatically log errors to Sentry.

  • SENTRY_DSN - the Data Source Name (DSN) for Sentry
  • SENTRY_CURRENT_ENV - the environment tag to pass to Sentry, for example production
  • GOVUK_STATSD_PREFIX - a Statsd prefix like govuk.apps.application-name.hostname (deprecated; statsd functionality will be removed in a future release)

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.

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 = ->(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.

Open Telemetry

To enable Open Telemetry instrumentation for Rails set the ENABLE_OPEN_TELEMETRY=“true” environment variable.

Prometheus monitoring

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

require "govuk_app_config/govuk_prometheus_exporter"

Statsd (deprecated)

⚠️ Statsd support is deprecated and will be removed in a future major release of govuk_app_config.

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

To enable production-like logging, an env variable GOVUK_RAILS_JSON_LOGGING is set in the govuk-helm-charts and then checked in railtie.rb. This will allow JSON format logs and Govuk-Request-Id to be visible.

For development logs, in order to see the production style logs, developers should set GOVUK_RAILS_JSON_LOGGINGin govuk-docker -> docker-compose files.

Logger configuration

To include additional custom fields in your Rails logs, you can declare them within a GovukJsonLogging.configure block in a config/initializers/ file.

Example of adding a key/value to log entries based on a request header:

GovukJsonLogging.configure do
  add_custom_fields do |fields|
    fields[:govuk_custom_field] = request.headers["GOVUK-Custom-Header"]

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:


Internationalisation 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.


MIT License