marlowe
Description
marlowe provides a correlation id header for Rails and Rack applications to correlate logs for a single request across multiple services.
Install
You can install it as a gem:
$ gem install marlowe
or add it into a Gemfile:
gem 'marlowe'
Configuration
There is no configuration as of yet. Future plans include configuring the name of the correlation id header.
Accesing the Correlation ID
The correlation id can be accessed throughout the application by accessing the RequestStore storage.
RequestStore[:correlation_id]
Logging
For a rails application, you simply need to change the log formatter to one of the provided ones. Correlated versions of both the SimpleFormatter and Formatter are included.
# config/environments/development.rb
Rails.application.configure do
config.log_formatter = CorrelatedSimpleFormatter.new
end
To create your own formatter, you’ll need to access the RequestStore storage. You can use this pattern if you’ve rolled your own logger/formatter:
# lib/correlated_formatter.rb
require 'request_store'
class CorrelatedSimpleFormatter < ActiveSupport::Logger::SimpleFormatter
def call(severity, , progname, msg)
"[#{RequestStore.store[:correlation_id]}] #{super}"
end
end
Clients
Catching and creating the correlation ID is a great all on its own, but to really take advantage of the correlation in a service based architecture you’ll need to pass the id to the next service in the change.
Here’s an example of a Hurley client:
# lib/correlated_client.rb
require 'hurley'
require 'request_store'
class Hurley::CorrelatedClient < Hurley::Client
def initialize(*args, &block)
super
header['Correlation-Id'] = ::RequestStore.store[:correlation_id]
end
end
If you have long-lived Hurley clients, it is also possible to use the Hurley callback machanism to add the outgoing headers:
client.before_call do |request|
request.header['Correlation-Id'] = ::RequestStore.store[:correlation_id]
end
or
class Correlator
def name
:correlator
end
def call(request)
request.header['Correlation-Id'] = ::RequestStore.store[:correlation_id]
end
end
client.before_call(Correlator.new)