Dispatch rider is a pub/sub kind of library that allows you to publish a message to a notification system (like Amazon SNS) and then you can subscribe to the channels that you subscribed to and start handling the messages. Essentially making it a multi-service background job system.
Add this line to your application's Gemfile:
gem 'dispatch-rider'
And then execute:
$ bundle
Or install it yourself as:
$ gem install dispatch-rider
If you are using DispatchRider with rails, run the installer:
$ rails generate dispatch_rider:install
Setting up a publisher is simple.
All configuration can be loaded from a hash instead of being done like the examples below. (currently only implemented for the publisher)
You can set the global configuration using either a hash:
DispatchRider::Publisher.configure({
notification_services: {
file_system: {}
},
destinations: {
file_foo: {
service: :file_system,
channel: :foo,
options: {
path: "test/channel",
}
}
}
})or a block:
DispatchRider::Publisher.configure do |config|
config.parse({
notification_services: {
file_system: {}
},
destinations: {
file_foo: {
service: :file_system,
channel: :foo,
options: {
path: "test/channel",
}
}
}
})
endThen anytime you call configure on a new publisher, it will default to global configuration.
DispatchRider::Publisher.new
# is the same as
DispatchRider::Publisher.new(DispatchRider::Publisher.configuration)Alternatively, you can create your own configuration and load that configuration into your new publisher.
config = DispatchRider::Publisher::Configuration.new({
notification_services: {
file_system: {}
},
destinations: {
file_foo: {
service: :file_system,
channel: :foo,
options: {
path: "test/channel",
}
}
}
})
DispatchRider::Publisher.new(config)You can load this configuration hash from a YAML file or something, whatever works well for your environment.
To publish using the filesystem register the path where to publish the message files.
publisher = DispatchRider::Publisher.new
publisher.register_notification_service(:file_system)
publisher.register_destination(:local_message_queue, :file_system, :dev_channel, :path => "tmp/news-updates")
publisher.publish(:destinations => :local_message_queue, :message => {
:subject => "read_news",
:body => {"headlines" => [
"April 29, 2013: Rails 4.0.0.rc1 is released.",
"May 14, 2013: Ruby 2.0.0-p195 is released"
]
}})To publish using AWS::SNS make sure AWS.config has been setup.
It's then as easy as providing the configuration details of the topic to the publisher.
publisher = DispatchRider::Publisher.new
publisher.register_notification_service(:aws_sns)
publisher.register_destination(:sns_message_queue, :aws_sns, :dev_channel, {
:account => 777,
:region => 'us-east-1',
:topic => 'RoR'
})
publisher.publish(:destinations => :sns_message_queue, :message => {
:subject => "read_news",
:body => {"headlines" => [
"April 29, 2013: Rails 4.0.0.rc1 is released.",
"May 14, 2013: Ruby 2.0.0-p195 is released"
]
}})To publish to multiple destinations:
publisher.publish(:destinations => [:local_message_queue, :sns_message_queue], :message => {
:subject => "read_news",
:body => {"headlines" => [
"April 29, 2013: Rails 4.0.0.rc1 is released.",
"May 14, 2013: Ruby 2.0.0-p195 is released"
]
}})Sample Rails publisher:
# app/publishers/news_update
class NewsPublisher < DispatchRider::Publisher::Base
destinations :sns_message_queue
subject "read_news"
def self.publish(news)
new.publish({"headlines" => news.headlines})
end
endYou can configure the subscription side of DispatchRider by using the built in configuration object.
DispatchRider.config do |config|
config.before(:initialize) do
# code to run before initialize
end
config.after(:process) do
# code to run after process
end
# allows you to wrap a callback around the execution of each job
config.around(:dispatch_message) do |job, message|
some_block_around do
job.call
end
end
config.logger = Rails.logger
# Log Formatter
# Text Formatter (default)
# config.log_formatter = DispatchRider::Logging::TextFormatter.new
# JSON Formatter
# config.log_formatter = DispatchRider::Logging::JsonFormatter.new
config.default_retry_timeout = 300
config.error_handler = DispatchRider::DefaultErrorHandler # an object that responds to .call(message, exception)
config.queue_kind = :sqs
config.queue_info = { name: "queue-production" }
config.handler_path = Rails.root + "app/handlers" # path to handler files to be autoloaded
endOptions:
logger: what logger to use to send messages to (responds to the standard ruby Logger protocol), defaults to a new Logger sending messages to STDERRlog_formatter: what log formatter to use with logger, defaults to DispatchRider::Logging::TextFormatter.new
Dispatch rider supports injecting callbacks in a few parts of the lifecycle of the process. Each
callback can have hooks plugged into it at before, after and around the execution.
This callback is called when the runner is being initialized.
Block Arguments:
- None
DispatchRider.config do |config|
config.before(:initialize) do
# your code here
end
config.around(:initialize) do |job|
# your code here
job.call
# your code here
end
config.after(:initialize) do
# your code here
end
endThis callback is called when the message is being published.
Block Arguments:
- message:
[DispatchRider::Message]-- message that is about to be sent - destinations:
[Array<Symbol>]-- list of destinations to sent to
DispatchRider.config do |config|
config.before(:publish) do |message:, destinations:|
# your code here
end
config.around(:publish) do |job, message:, destinations:|
# your code here
job.call
# your code here
end
config.after(:publish) do |message:, destinations:|
# your code here
end
endThis callback is called when the runner is running its event loop.
Block Arguments:
- None
DispatchRider.config do |config|
config.before(:process) do
# your code here
end
config.around(:process) do |job|
# your code here
job.call
# your code here
end
config.after(:process) do
# your code here
end
endThis callback is called when executing a single message.
Block Arguments:
- message
[DispatchRider::Message]-- the message received fromDispatchRiderqueue
DispatchRider.config do |config|
config.before(:dispatch_message) do |message|
# your code here
end
config.around(:dispatch_message) do |job, message|
# your code here
job.call
# your code here
end
config.after(:dispatch_message) do |message|
# your code here
end
endTo setup a subscriber you'll need message handlers. The handlers are named the same as the message subjects. Each handler may also specify a retry_timeout as shown below. When a job throws an exception it will be put back on the queue in that time period if the queue supports timeouts. If the underlying queue (such as filesystem) does not support retry then this setting is ineffective.
Sample message handler:
# app/handlers/bar_handler
class ReadNews < DispatchRider::Handlers::Base
def process(message_body)
message_body["headlines"].each do |headline|
puts headline
end
end
def retry_timeout
10.minutes
end
endIf you have a long running job, or if you wish to retry a job later, you may use two methods in your handler class. return_to_queue and extend_timeout.
return_to_queue will retry your item immediately. extend_timeout will tell the queue you wish to hold this item longer.
# app/handlers/foo_handler
class LongRunning < DispatchRider::Handlers::Base
def process(body)
my_loop.each do |item|
#... do some work ...
extend_timeout(1.hour)
end
rescue OutOfResourcesImOutError
return_to_queue #oops! Better give this to somebody else!
end
endSample subscriber setup:
subscriber = DispatchRider::Subscriber.new
subscriber.register_queue(:aws_sqs, :name => "news-updates")
subscriber.register_handler(:read_news)
subscriber.setup_demultiplexer(:aws_sqs)
subscriber.processSample subscriber dispatch error handling (optional):
# using objects
module ErrorHandler
def self.call(message, exception)
# put your error handling code here
return false # or return true to permanently remove the message
end
end
subscriber.setup_demultiplexer(kind, ErrorHandler)
# using lambdas
error_handler = ->(message, exception) do
# put your error handling code here
return false # or return true to permanently remove the message
end
subscriber.setup_demultiplexer(kind, error_handler)Airbrake is supported out of the box. All you need to do is:
- Install and configure the airbrake gem.
- Use the
DispatchRider::AirbrakeErrorHandler.
subscriber.setup_demultiplexer(kind, DispatchRider::AirbrakeErrorHandler)or set it up in the config ...
DispatchRider.config do |config|
config.error_handler = DispatchRider::AirbrakeErrorHandler
endScheduled jobs currently require ActiveRecord. Support for other ORM will be added in the future depending on demand.
- Add and run the DB migration below:
class CreateScheduledJobsTable < ActiveRecord::Migration
include DispatchRider::ScheduledJob::Migration
def change
create_scheduled_jobs_table
end
end- Schedule jobs:
# Use `#publish_later`
class NewsPublisher < DispatchRider::Publisher::Base
destinations :sns_message_queue
subject "read_news"
def self.midnight_publish(news)
new.publish_later("headlines" => news.headlines, at: Date.tomorrow.midnight)
end
end
# Or create a scheduled job manually
DispatchRider::ScheduledJob.create! scheduled_at: Date.tomorrow.midnight,
destinations: [:sns_message_queue],
message: {
subject: "read_news",
body: { "headlines" => news.headlines }
}- Run scheduled publishing.
# Run once
# Ideally run on a cron. Where the cron is responsible for the publishing
# frequency. Any jobs due at the time this is run by the cron will be
# published.
DispatchRider::ScheduledJob.publish_due_jobs
# Loop. Warning: Loops are blocking. Run this on a separate thread if it's not
# the sole purpose of the app.
# publish every minute
DispatchRider::ScheduledJob.publish_due_jobs every: 1.minute
# publish every half an hour
DispatchRider::ScheduledJob.publish_due_jobs every: 30.minutesSee DEPLOYING.md
- Fork it
- Create your feature branch (
git checkout -b my-new-feature) - Commit your changes (
git commit -am 'Add some feature') - Push to the branch (
git push origin my-new-feature) - Create new Pull Request
Copyright (c) 2015 PayrollHero Pte. Ltd.
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