VetebraNanite

George Palmer

Background processing

• Work should be moved to the background to stop application server load

• This keeps website responsive

• Useful for: images, videos, web services, slow database queries....anything that isn’t quick!

Current background offerings

• Fork into background of rails process

• eg spawn, run_later

• Record to database (or file) and background daemon picks up from there

• eg background_job, delayed_job

• Fork onto some kind of queue

• eg backgroundRB, beanstalk, starling with workling

Introducing Nanite

• Developed by EngineYard

• Gives presence - we know what’s available

• Handles failure

• Instant scalability

• Event based architecture

Pre-reqs

• Erlang

• Not R12B5 (the version installed by MacPorts)

• RabbitMQ

• Untar to erlang lib directory - most likely /usr/local/lib/erlang/lib

AMQP

• Advanced Message Queuing Protocol

• Enterprise quality protocol developed by several financial institutions

• Includes wire protocol to ensure language neutral

• RabbitMQ implements AMQP 0.8

Installing AMQP for Ruby

$ sudo gem install eventmachine

$ git clone git://github.com/tmm1/amqp.git

$ cd amqp && rake gem && sudo gem install amqp-<version>.gem

NaniteThinApp

Server

AMQP

Nanite

Nanite Mappers Nanite Agents

RubyScript

Nanite

AMQP

AMQP

NaniteActor

NaniteActor

AMQP

NaniteActor

NaniteActor

m e s s a g e s

Nanite Mappers

• Control and track work

• Unlimited number can be run that get updates from mapper exchange

• mapper exchange itself is just a heartbeat and registration MQ

• Run either inside Rails/MERB app (on Thin) or via command line

Nanite Agents

• Do the work

• A given nanite agent can have multiple actors

• Scale by adding more agents

• Pings the mapper exchange every @ping_time seconds to report health

Nanite Actors

class Manor < Nanite::Actor expose :name

def name(vars) # Do something interesting here :result => “RubyManor” endend

Nanite::Dispatcher.register(Manor.new)

Agent directory structure

+ myagent

+ actors

- manor.rb

+ files

- init.rb

- config.yml

Agent config.yml---

:vhost: /nanite # Allow multiple agents with different queues [compulsory]

:user: nanite # Username for queue

:pass: testing # Password for queue

:identity: barney # Can be auto-generated but useful to send work to specific

# agents

:file_root: path # where to store any transfered files

:format: marshal # or :json

# Additional options include host and port. All options can be passed into

# nanite command so can avoid config file if want

Getting Started...

• Start RabbitMQ

• /usr/local/lib/erlang/lib/rabbitmq/sbin/rabbitmq-server

• On first run nanite/bin/rabbitconf

• Sets up RabbitMQ with a vhost and users for that vhost (more on this later)

Starting agents

• cd <agentdir> && <nanite basedir>/bin/nanite

• I’ve been using:cd <agentdir> && <nanite basedir>/bin/nanite -t <identity> &

• Could be managed better through a daemon/monitoring system though

Offloading work to Nanite

• Use the following code:Nanite.request(callable, params = ‘’, options = {}) {|res| # use res to do something}

• callable is the actor and method - eg ‘/manor/name’

• params are parameters for the callable method - eg ‘2008’

• options includes timeout, target and the routing algorithm - more on this later

Interfaces into the Mappers

• Via console:

• nanite/nanite-mapper -i

• Via command line:

• See nanite/examples/cli.rb

• Via Rails/MERB app:

• See next slide....

Rails/MERB & Nanite# Updates the userdef update ... if (@user.save) Nanite.request(‘/updates/twitter’, ‘georgio_1999’) {|res| # This block won’t execute until the event fires @user.status = res[:status] @user.save } endend

def ajax_call # Must use database for state and not Nanite jobend

Allocation of work

• The pings are used by the mappers to find the healthiest nanite agents

• If a nanite agent doesn’t ping inside a window it is removed from the active list (until it does ping again)

• perfect for busy or error hit nanites

• The default routing algorithm is based on server load

Routing options

• In options argument of Nanite.request you can choose:

• selector

• :least_loaded (default), :all, :random, :rr

• target - use this to target a specific agent

• timeout - override the default timeout (60s)

Custom algorithms

• Nanites report state with their ping

• By default this is the server load

• Can override this by adding code to agent init.rb

• Nanite.status_proc = lambda { MyApp.some_statistic_indicating_load }

• Must be comparable

• Can use with existing routing algorithms or create own more complex ones

File transfers

• Nanite can handle file transmission

• Agents subscribe (for all actors) in init.rb or Actors subscribe individually:

• Nanite.subscribe_to_files(domain)

• Mappers send via:

• Nanite.broadcast_file(filepath, opts)

• where opts can contain :domain and :destination (destination filename)

The beauty of JSON

• Nanite is built on top of AMQP, so if the queue items are serialised using JSON...

• Then Nanite isn’t needed at the agent side

• Any AMQP implementing daemon can read message and respond

• Useful for legacy code (or legacy people)

Understanding Security

• Security is implemented using RabbitMQ’s vhosts and username/passwords

• The username/password is defined in config.yml for each nanite

• Need to configure RabbitMQ using the rabbitmqctl command

• Generally one vhost per application

Let’s play

• cd <git_resources>/nanite/examples/myagent

• ../../bin/nanite -t <identity> -h <host>

• Let’s use fullname for identity - eg georgepalmer

• Should see something like:# subscribing to file broadcasts for foobar

# loading actor: /Users/georgepalmer/work/git_resources/nanite/examples/myagent/actors/gems.rb

# loading actor: /Users/georgepalmer/work/git_resources/nanite/examples/myagent/actors/mock.rb

# "advertise_services"

# ["/gems/list", "/mock/list"]

Resources

• RabbitMQ: http://www.rabbitmq.com

• Ruby AMQP with RabbitMQ tutorial: http://hopper.squarespace.com/blog/2008/7/22/simple-amqp-library-for-ruby.html

• Nanite: http://github.com/ezmobius/nanite

• Doc isn’t great, code is very readable