Last updated: 4 Jul 2024

govuk_app_config: Health Checks

GOV.UK apps often have special /healthcheck routes, which give an indication of whether the app is running and able to respond to requests. Read about how health checks are used.

Including checks in your app

Set up a route in your rack-compatible Ruby application, and pick the built-in or custom checks you wish to perform.

For Rails apps:

get "/healthcheck/ready", to: GovukHealthcheck.rack_response(
  GovukHealthcheck::SidekiqRedis,
  GovukHealthcheck::ActiveRecord,
  CustomCheck,
)

It also accepts objects, so classes can be initialized:

get "/healthcheck/ready", to: GovukHealthcheck.rack_response(
  InitializedCheck.new(:param),
)

Built-in checks you can use include:

• GovukHealthcheck::RailsCache - checks that the Rails cache store, such as Memcached, is acessible by writing and reading back a cache entry called "healthcheck-cache".

• GovukHealthcheck::Redis - checks that the app can connect to Redis by writing and reading back a cache entry called "healthcheck-cache".

• GovukHealthcheck::Mongoid - checks that the app has a connection to its Mongo database via Mongoid.

• GovukHealthcheck::SidekiqRedis - checks that the app has a connection to Redis via Sidekiq.

• GovukHealthcheck::ActiveRecord - checks that the app has a connection to the database via ActiveRecord.

Writing a custom healthcheck

A check is expected to be a class with the following methods:

class CustomCheck
  def name
    :the_name_of_the_check
  end

  def status
    if critical_condition?
      :critical
    elsif warning_condition?
      :warning
    else
      :ok
    end
  end

  # Optional
  def message
    "This is an optional custom message that will show up in the alert in Icinga"
  end

  # Optional
  def details
    {
      extra: "This is an optional details hash",
    }
  end

  # Optional
  def enabled?
    true # false if the check is not relevant at this time
  end
end

It is expected that these methods may cache their results for performance reasons, if a user wants to ensure they have the latest value they should create a new instance of the check first.

Put custom health checks for your app into a Healthcheck module. Each custom check class should end with Check.