Saturday, 5 May 2012

PaaS (Platform as a Service)–The Choice for New Applications on Cloud

PaaS or Platform as a service as a concept has been well received, however one really needs to understand when is it likely to hit the mainstream. In this post I will start with the the basics of PaaS and IaaS, dig deeper into PaaS,  notes on Windows Azure PaaS programming model & lastly what’s the roadmap of Windows Azure really looking like. As usual a disclaimer “ this post is my personal views I don’t write for MSFT”. Humble request to the readers would really love have some feedback. Happy reading…

Cloud platform technologies are broadly divided into 2 categories PaaS & IaaS. Amazon Web Services(AWS) Elastic Cloud (EC2) first hit the market in IaaS segment. PaaS is something we are given to believe is expected to hit  the mainstream soon, the question is when & with the new developments I see the timeline just stretching.

The key point is that IaaS is dominant in the market, its about 10 times the market share of PaaS (courtesy:Gartner Inc.). It sounds little disruptive but Azure is adding true IaaS support by the end of this year.

If we look into Windows Azure today which is purely PaaS what exists as of current in the Azure Platform is

  • Web/Worker roles
  • Persistent VM roles expected to hit the market later this year. (VM Roles already exist as of current and are not very useful). Persistent VM Role is true IaaS functionality.
  • Web Sites expected to hit the market later this year.


Getting Definitions right….

Understanding IaaS:  Understanding IaaS from a scenario per say. 


From an example standpoint of explaining IaaS , a developer is running a multi tier application and has to deploy this application on a cloud would include the following steps

  • Choose a pre installed VM which included the OS & the database.
  • Choose a pre installed VM which included the OS and Application support such as IIS
  • Provision database and create the tables and add data
  • Install application
  • Configure the load balancer
  • From time to time manage the VM’s and DBMS from a patch management point of view.


Understanding PaaS

If one needs to deploy the same application on the PaaS platform, it would look some what like below. The PaaS platform come pre installed with the Database, Application and load balancer


The steps involved in deploying the application are only 2

    • Provision database and create the tables and add data
    • Deploy the application

From the abovementioned scenarios PaaS seems much simpler and this simplicity will drive the usage of PaaS in the future.

Benefits of PaaS 

  • PaaS is faster
    • Reason: Theirs is less work for developers to do
    • Benefit: Applications can from idea to availability more quickly.
  • PaaS is Cheaper
    • Reason: There’s less administrative work to do
    • Benefit: Organizations spend less supporting applications
  • PaaS is lower risk
    • Reason: Platform gives so much predefined , the window of error is reduced
    • Benefit:Creating and running applications gets more reliable.

* With all these benefits IaaS is 10 times more popular the question how come? The answer is fairly complex and will explain in the remaining of the post

Drawbacks of PaaS

  • Unfamiliar for developers
    • Its harder to adopt because they much learn the PaaS platform
  • Developer have less control
    • They must work within the constraints of the PaaS technology. Each PaaS technology is different from another comparing Azure from AWS quite different. There is no standardization so moving across PaaS platforms can become very difficult
  • PaaS isn’t identical to an existing on premise environment
    • This can raise fears of vendor lock in , example is PaaS is completely different and building an application on that can mean married to the same for life.
    • Moving existing on premise application to PaaS can be hard. There can be a considerable amount of rewrite on moving existing applications to PaaS.
  • PaaS supports fewer useful scenarios  than IaaS . IaaS in its current form is much more flexible to allow on premise application to move to cloud.Lets take a quick comparison from scenario standpoint between PaaS & IaaS


Scenarios IaaS PaaS
Running New Cloud Native Application Yes Yes
High Performance Computing and Big Data Yes Probably
Running a Standard Database Yes No
VM’s for a Dev/Test Lab Yes No
Running existing Web App/Sites Yes Maybe
Running Standard Packaged Apps Yes No
Virtual Data Center (VM;s for on Demand Use) Yes No
Disaster / Recovery similar to the on Premises world Yes No
  • Running New Cloud Native Application works fine on PaaS as long one does have issues with the vendor lock.
  • HPC and Big Data very apparent in IaaS world, in the PaaS still getting there, again moving an existing HPC on premise to PaaS may not be possible
  • Running a Standard Database such as Sql Server or Oracle is not supported by PaaS as of current.
  • VM’s for Dev/Test Lab not possible on PaaS
  • Running existing Web App/Sites on PaaS not possible as of today
  • Running Standard Packaged Application such as SAP, SharePoint on PaaS not possible.
  • Virtual Data Center a fantastic offering from IaaS not possible on PaaS
  • Disaster Recovery , IaaS can be a good foundation which replicates the on premise world on cloud. PaaS however cannot do that.

IaaS addresses a lot more scenarios than PaaS. On the contrary there is still an argument i.e cost of operation Vs. abstraction.

Cost of Operation Vs. Abstraction

From a cost of operation standpoint the physical machines are the most costly and least level abstraction, then came virtual machines which brought down the cost further and increased the level of abstraction.Subsequent to this we see the IaaS which reduced cost of operation further and increased the level of abstraction further. Finally came PaaS which reduces the cost of operation further and increased level of abstractions. How long will it take for the enterprise take to move into PaaS no correct answer?


Benefits of PaaS – A Closer Look

Dwelling into the benefits of PaaS the platform on which the conclusion are drawn is Windows Azure. Looking at following key parameters

  • Application Design
  • Application Development
  • Application Test
  • Application Deployment
  • Storage
  • Administration & Management


Application Design

  • The starting point on Application Design on PaaS is at much higher level from a design point of view there are lesser things to do.
  • Virtualized Images which is important in IaaS one doesn’t need to bother in PaaS. So in way one need not look at security too much in depth when designing for PaaS
  • Designing for redundancy at a VM level is not required as PaaS manages it internally


Application Development

  • PaaS provides a lot more services than IaaS a developer needs to write lesser code.
  • PaaS hides most of the configuration related stuff and developer has to do very little. In scenario where you have teams working globally integration problems stemming from diverse environment are reduced as there is very little for configuration and the environment is one (Azure).


Application Testing

  • As there is lesser code to write apparently there is lesser code to test
  • Azure provides single environment to test
    • Teams don’t need their own test platform
    • Test teams don’t need to understand and track configuration changes

Application Deployment

  • One key thing in PaaS as a developer one gives the tested code to the PaaS platform (assuming the role level segregation) and PaaS is responsible for deploying, so the timeline for deployment comes down in contrast to this IaaS is the same as on premise deployment.
  • Another important feature of PaaS is “in place update without downtime”. Updated applications can be deployed in place without any downtime. Again this is a platform feature.
  • Caching and Storage is inbuilt feature of PaaS , developer can use this in their code without really bothering about the setup or configuration related details.


  • Considering one is using on cloud storage there is zero administration.
  • HA comes in automatically
  • Data is replicated automatically: Doing backup solely for recovery failure is less necessary.


Administration and Management

  • No need for administrators
  • No need to management team


*In my next post I will be publishing a comparison of the actual data on timeline for building an on-premise application vs. on a PaaS platform & the complexities associated with the same


 Getting Into Windows Azure Programming Model

Why is there a need to create a new programming model?

The PaaS platform comes with a lot of pre canned features and in order to effectively use it one has to follow a certain discipline which eventually is a new programming model.

PaaS sets in some ground rules… they are

  • Role Segregation: PaaS ideally segregates the applications into roles ex: web role, worker
    • Web Role which accepts request from users (Web Role synonymous to IIS)
    • Worker Role: Runs code
  • Multiple Instances: PaaS application runs multiple instances of each role. PaaS has an SLA of 24X7 availability so the bare bone requirement of this is 2 instance to manage HA. Its not mandatory to have 2 instances of each role and function without HA.
  • Application Behavior: If one of roles (which the application is hosted) fails the applications should behave correctly.  Its required that Application have to survive failure of any instance. This is a hard rule. What does it mean
    • Storage must be external to Web/ Worker role instance. An instance shouldn’t store data locally.  It should use Sql Azure , Tables or blobs to store the state. Most of us many think of the lines of components been stateless. Stateless is a confusing term.
    • Interaction between Roles should be generic: In other words Web/Worker role should not care which instance of another role it interacts with. Example a Web role instance in time may open a tcp/ip connection to a specific worker role and hope that the worker role continues to live in the bigger scheme of things. Understanding the basic premises that communications across roles also needs to be loosely coupled and the expectation that next time the web role is going to connect to the same worker role is not appropriate as “The worker role may been recycled and all the state is lost. Go with the basic assumption that any role can fail any time and that’s way the PaaS platform wants you to build.
    • No Sticky Sessions in PAAS:  A client shouldn’t assume that all of its request will be handled by the same Web Role Instance.

There are constraints around how you build the application which needs to run PaaS there is a rationale as to why these constraints have come into existence.

Fabric Controller – A Background

Most PaaS implementation has this component called the Fabric Controller and all the machines in a particular data center are its ownership.

  • It creates and monitors role instances on those machines.
  • It starts new instances when – a new application is deployed or an running application fails or when it needs to update system software in an instance virtual or physical machine.
  • The FC is smart enough not to assign the same roles of the application on the same physical machine.

Fabric Controller 101….

Lets say we have a set of computers to be exact 40 of them each with 4 cores. We have a total of 160 cores at our disposal. There is a need to run a variety of applications on these cores. So architecturally speaking I would need a central software which we call is a Controller and I would need Agents installed on all the computers.

1.An application run request would come to the Controller. The controller has a complete inventory which computer and which core is been assigned to what application.

2.The controller finds the appropriate computer passes the application binaries to agent (computer) which in turn has running virtual instances of Windows Server 2008 .

3.The agent picks up one of the virtual instances and hands them over the binaries.

4.The application binaries are scanned for the type of role if it’s a web role the binaries are copied to c:\inetpub\wwwroot\ creates a virtual directory & application sends the endpoint back to the agent.

5.The agent in turn sends the physical endpoint to the controller.

6.The controller registers the endpoint into some kind of registry. The logical endpoint is something which is given to the end-user.

7. The FC can kill any of running instance at any point of time.

Somewhere in the description one will soon realize there is an service bus also initially called the internet service bus.


Microsoft’s Fabric Controller

Microsoft’s data center stores all the data of Windows Azure storage and all Windows Azure applications. Windows Azure Fabric Controller controls manages the servers, the set of machines which are dedicated to Windows Azure and the software that runs on the Microsoft Data Center. Windows Azure Fabric Controller is a distributed applications that is replicated among a group of machines.It has its own of resources in its own environment like computers, load balancers, switches etc. Windows Azure Fabric Controller can communicate with the fabric agent on each machine. It keeps track of all Windows azure application in the fabric.


This helps the Windows Azure Fabric Controller to perform useful activities like monitoring all the running applications. The Windows Azure fabric controller decides where new applications will run and also selects the physical server so that hardware is utilized optimally. This is achieved using the configuration information which is uploaded with each Windows Azure application. The FC controller achieves this using the configuration information which is uploaded with each application on Windows Azure. The configuration file is an XML file which explains the various instance of the application, the number of virtual machines to be created for the applications/

Because of this understanding the FC does a number of things like monitoring all running application, decides where a new application should run , optimize hardware utilization by choosing the physical server.

OpenStack Compute fabric controller is called Nova.

Windows Azure is a 1 million core machine and I’m assuming the FC in itself is Server Farms locally and distributed.


Interacting with the Operating System

In PaaS at any given point of time your code will never interact with the operating system directly , the FC own the OS. It updates each’s OS when necessary. Any changes made must be applied each time an instance starts. Any changes made from a configuration stand point have to reapplied each time an instance starts. In case there is a requirement to have software which is not already there at the platform level what does do.  This can be done in more than one ways lets say you need to have telerik support on your web role you need install this every time the role starts up. In case there are too many things to be installed the “time to get started will be too long” and this solution may not look feasible.

This is scenario we can use current VM role provided by Azure where the developer gets to supply the image but any changes to VM are lost at every restart this is a problem hence MSFT will be including persistent VM Role where the state is stored in the blob.

Summarizing- PAAS Programming Model

  • Application are more available and cheaper to run on PaaS
  • What it offers
    • Protection against hardware failures
    • Protection against software failures
    • No downtime application updates
      • With a single step update called the whipsaw
      • With a rolling update using update domain
    • No downtime system software updates
    • No administrative efforts

Moving Applications to Windows Azure PaaS

  • An ASP.NET application with multiple load balanced instance that share state stored in Sql Server
    • An easy move
    • Perfect fit for PaaS platform
  • An ASP.NET application that runs multiple instances that maintain per instance state and relies on sticky session
    • Requires some work
  • A client accessing WCF services running in a middle tier
    • If the service don’t maintain per client state between calls , an easy move
    • Otherwise some redesigning effort is required
  • An application with a single instance running on Windows Server that maintains state on its own machine
    • Some redesign needed
    • This application might run well in Persistent VM role.


Innovative Business Idea: Writing a Migration Tool for on premise windows application to Azure….

Introduces Web Sites in Azure

PaaS & IaaS are cloud platform technologies. Cloud computing and hosting which were 2 different worlds  years are no longer separate. Customers can now buy a wide range of platforms offering from various service providers which include IaaS & PaaS or could be buying hosting servers by the month.

Cloud categorization has predominantly understood as IaaS, PaaS & SaaS a more cleaner way to look is SaaS, IaaS, cloud Platforms like Azure, AWS & Private Cloud.

Hosting - Common Technology options today


Difference Between Hosting to Cloud Computing


Hosting & Cloud Computing- Categorizing options



Azure is likely offer monthly pricing for Persistent VM Role & Websites which are actually a part Windows Azure. Microsoft will also make WebSite software for service providers.

Windows Azure WebSites- Provides shared hosting for WebSites- Application can also access other Windows Azure roles.

WebSites are different from Web/Worker Roles on following accounts

  • Web Sites provides a standard IIS Web environment it supports sticky session. Web Role are stateless low admin application.
  • Web Sites will help in running existing Web Application unchanged on Azure as compared to Web Role which mandates a change depending on how the application is written
  • WebSites are shared on the same virtual instance on contrast Web Role which is dedicated to a virtual instance.
  • Web Sites are best suited for new and existing small to medium Web Sites/ app on contrary Web Role are meant for large cloud apps.
  • Application deployment for WebSites its liking a creating a new site on an existing VM on Web Role it’s a new VM Role
  • WebSites allow deployment of updates without downtime same as Web Role


Web Sites in Azure will help bring customer onto Azure with lesser effort this is a well thought out strategy for the long term.

Windows Azure provides multiple choices for the customer to move to cloud & it is worth the effort in terms of reduced costs.