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umbra 🌘

umbra /ˈʌmbrə/

noun

  1. the fully shaded inner region of a shadow cast by an opaque object, especially the area on the earth or moon experiencing the total phase of an eclipse.
  2. shadow or darkness. "an impenetrable umbra seemed to fill every inch of the museum"

umbra is a rack middleware that allows you to create shadow requests via a redis pub/sub channel.

Installation

Add this to your Gemfile

gem 'umbra-rb'

And then execute:

$ bundle

Or install it yourself as:

$ gem install umbra-rb

Usage

umbra is composed of two separate parts: a rack middleware and a shadower executable.

The rack middleware publishes a protobuf encoded version of an incoming request to a redis channel, the shadower subscribes to this channel and replicates the request a configurable amount of times.

Middleware

A minimal rack application using umbra would look like this:

# /config.ru
require 'rack'
require 'rack/lobster'
require 'umbra'

Umbra.configure

use Umbra::Middleware
run Rack::Lobster.new

If using Rails you can achieve the same via an initializer:

# /config/initializers/umbra.rb
require 'umbra'

Umbra.configure

Rails.application.config.middleware.use(Umbra::Middleware)

Config

umbra allows you to add custom configuration by passing a block to Umbra.configure. You may pass custom configuration in the following form:

Umbra.configure do |config|
  config.<config_option> = <config_value>
end
config_option default description
publisher Umbra::Publisher Must respond to call. By default, pushes the encoded rack request/response to a Queue that is consumed in a different thread and publishes to redis.
request_selector Umbra::RequestSelector / proc { true } Must respond to call. Determines whether request/response will be published
encoder Umbra::Encoder Must response to call. Encodes the rack request/response for publishing
error_handler Umbra::SupressErrorHandler / proc { nil } Must respond to call. Called on exception, is always passed the exception as first argument, may be passed rack environment and response.
redis_options {} Hash of options passed to Redis client. See Redis::Client docs
logger Logger.new(STDOUT) The logger to be used.

Shadower

Download the latest version from the latest releases page.

Or go get github.com/carwow/umbra

The following flags are available (run umbra -help):

-buffer int
    request buffer size (default 25)
-redis string
    redis connection string (default "redis://localhost:6379")
-replication float
    number of times to replicate requests (default 1)
-timeout duration
    http client timeout duration (default 5s)
-workers int
    number of concurrent workers (default 100)

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/carwow/umbra.

License

The gem is available as open source under the terms of the MIT License.