messaging

Rabbit MQ

AMQP broker
AMQP defines messaging protocol (http://amqp.org)
Written in Erlang
Queues or Message destinations configured via the AMQP protocol
Messages routed via Exchanges
Message Routing can be defined using client library (Ruby's amqp gem for example)
Message Store - File System based (in memory + disk) - http://www.rabbitmq.com/blog/2011/01/20/rabbitmq-backing-stores-databases-and-disks/

Active MQ

Broker, Messaging Bus
Supports AMQP protocol via configuration
AMQP not required though
Queues/Destination defined via configuration
Written in Java
JMS focussed
Can be used with other clients/languages
Default Message Store - KahaDB - file based message persistence database
Also supports most SQL based Databases as message store

MONGO DB

Capped Collection as a Message Bus
Message Store backed by Mongo
Suited for Pub/Sub
Node.js example (https://gist.github.com/3210919) mimics subscriber/broker behavior using "tailable" cursor

Rabbit MQ routing

rabbit mq routing

AMQP Exchange

Accepts messages from producer and routes them to message queues
Messages are always routed and published to Queues via Exchanges using pre-defined criteria called bindings
Binding - association between Exchange & Queue
Queue must be bound to at least one exchange to receive messages from publishers.
Exchange Types - Fanout, Direct, Topic, Headers
Message attribute routing_key is used by Exchange to route the message to its destination. Analogous to address.

Exchange

exchange = AMQP::Exchange.new(channel, :fanout, "nodes.metadata")

OR

exchange = channel.fanout("nodes.metadata")

Exchange/Queue Binding

Glue between Exchange and Queue

queue = channel.queue("queue.name", durable: true).bind(exchange)

queue.subscribe { |payload| puts "Queue #{queue.name} received #{payload}" }

Exchange - Fanout

Exchange - Direct

exchange - direct

exchange = AMQP::Exchange.new(channel, :direct, "nodes.metadata")

OR

exchange = channel.direct("nodes.metadata")

exchange - direct

queue = channel.queue("queue.name").bind(exchange, routing_key: "routing.key")

queue.subscribe { |payload| puts "Queue #{queue.name} on channel received #{payload}" }

exchange.publish("Hello, direct exchanges world!", routing_key: "routing.key")

routing key - pattern

channel.queue("us.california").bind(exchange, routing_key: "americas.north.us.ca.*").subscribe

{ |metadata, payload| }

exchange.publish("San Diego update", routing_key: "americas.north.us.ca.sandiego")

exchange.publish("Berkeley update", routing_key: "americas.north.us.ca.berkeley")

AMQP Ruby library - Connection

require "amqp"

EventMachine.run do

# using AMQP.connect with a block

AMQP.connect(host: "localhost") do |connection|

# connection is open and ready to be used

end

AMQP RUBY LIBRARY - CONNECTION

require "amqp"

EventMachine.run do

# using AMQP.connect with a block

client = AMQP.connect(host: "localhost", username: "hedgehog", password: "pwd")

# channel object used to create Exchange and Queue

channel = AMQP::Channel.new(connection)

end

AmQp Queue

FIFO Message Buffers
Exchange route/store messages to Queue
Queue has a name to uniquely identify it
Queue are declared before they can be used
Declaring a queue will create it, if it does not exists
AMQP Broker will name a queue, if no name is provided by the client
Queue needs to bind to an exchange to receive messages
Queue Types - Durable Shared & Exclusive In-memory

AMQP - Durable queue

queue = AMQP::Queue.new(channel, "images.resize", durable: true)

Durable keys can be accessed by multiple consumers and from different process

AMQP - Exclusive queue

channel.queue("images.resize", auto_delete: true, exclusive: true)

Exclusive queues may only be accessed by the current connection and are deleted when that connection closes