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From: Kelven Yang <kelven.yang@citrix.com>
To: "cloudstack-dev@incubator.apache.org"
	<cloudstack-dev@incubator.apache.org>
Date: Tue, 14 Aug 2012 23:04:32 -0700
Subject: [Discuss] CloudStack architecture to a loosely-coupled component
 oriented distributed architecture
Thread-Topic: [Discuss] CloudStack architecture to a loosely-coupled
 component oriented distributed architecture
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I know everyone is recently busy and excited for the first Apache release
of CloudStack, hopefully we still have some bandwidth for discussions
about architecture fine-tunes, here is one for discussion.

Conceptually, current CloudStack works very much like an JaveEE
application server container, given the scale of all our current cloud
deployments with CloudStack, I think CloudStack has done a great job.

Running as an application server container, it brings us a lot of benefits
like easy to deploy, efficient resource utilization, etc, but in the mean
time, as modules inside a container are too easy to be involved tightly,
over time, as we add more and more features, the complexity of overall
system increases dramatically. Moving forward, it makes a lot of sense to
reshape CloudStack from a module container to be a component oriented
distributed platform.

Component
Component is an independent deployment unit in a distributed
environment(i.e., CloudStack), it usually runs as a separated process, can
be independently scaled and has independent communication endpoint. It
should have simple bindings to the distributed environment instead of
requiring a complex container, to communicate with other components in the
system, it should use bi-directional principal for loose-coupling and
service-oriented, which is, using light-weight messaging event
notification in one direction and service-oriented interaction at another
direction.

Module
Module is a logic software unit that encapsulates software functions with
well defined programming interface, a component contains one or more
software modules

Component Service
Software service that is provided at component level, usually in shape of
web service or REST-ful service

Messaging
A process for components to notify each other by exchanging messaging
events

Messaging event
A package of information that is uni-casted or broadcasted to the
destination component(s)

Service discovery
A process for component to discover services and endpoint bindings within
the environment, it could be either through a directory service provided
at infrastructure level or through auto-discovery

Under component oriented principal, at high level CloudStack core can be
fine-tuned to a number of (not limited to) components

API component
Implements CloudStack API, it also initiates logic orchestration flows
(i.e., deploy a VM) which will be notified and picked up in Orchestration
engine component

Orchestration Engine component
This components is the heart to drive all async-flows currently active in
the system, it orchestrates high-level flow through messaging among
networking/storage/compute components.

Data service component
This components provides the data service for objects within the Cloud.

Networking component
A component to implement networking provisioning

Storage Component
A component to implement storage provisioning

Compute Component
A component to implement hypervisor VM provisioning

Fabric Monitoring Component
A component dedicated for monitoring on fabric resources, for example,
monitoring of hypervisor host status
=20
Fabric Admin Component
A component that implements fabric resource administration.

Service Framework Component (module?)
A component(or a module inside Orchestration Engine?) to provide service
to launch component service in a VM and auto-scale the component service.

At middleware level, we will need a messaging event delivery platform and
middleware level synchronization system, possible candidates could be
Redis and Apache ZooKeeper.


Kelven