Buck Woody : Cloud Computing, Web, Compute

Why do I need two Instances in Windows Azure?

BuckWoody — Tue, 20 Mar 2012 13:23:00 GMT

Windows Azure as a Platform as a Service (PaaS) means that there are various components you can use in it to solve a problem:

Compute “Roles” - Computers running an OS and optionally IIS - you can have more than one "Instance" of a given Role
Storage - Blobs, Tables and Queues for Storage
Other Services - Things like the Service Bus, Azure Connection Services, SQL Azure and Caching

It’s important to understand that some of these services are Stateless and others maintain State. Stateless means (at least in this case) that a system might disappear from one physical location and appear elsewhere. You can think of this as a cashier at the front of a store. If you’re in line, a cashier might take his break, and another person might replace him. As long as the order proceeds, you as the customer aren’t really affected except for the few seconds it takes to change them out. The cashier function in this example is stateless.

The Compute Role Instances in Windows Azure are Stateless. To upgrade hardware, because of a fault or many other reasons, a Compute Role's Instance might stop on one physical server, and another will pick it up. This is done through the controlling fabric that Windows Azure uses to manage the systems.

It’s important to note that storage in Azure does maintain State. Your data will not simply disappear - it is maintained - in fact, it’s maintained three times in a single datacenter and all those copies are replicated to another for safety. Going back to our example, storage is similar to the cash register itself. Even though a cashier leaves, the record of your payment is maintained.

So if a Compute Role Instance can disappear and re-appear, the things running on that first Instance would stop working. If you wrote your code in a Stateless way, then another Role Instance simply re-starts that transaction and keeps working, just like the other cashier in the example.

But if you only have one Instance of a Role, then when the Role Instance is re-started, or when you need to upgrade your own code, you can face downtime, since there’s only one. That means you should deploy at least two of each Role Instance not only for scale to handle load, but so that the first “cashier” has someone to replace them when they disappear. It’s not just a good idea - to gain the Service Level Agreement (SLA) for our uptime in Azure it’s a requirement. We point this out right in the Management Portal when you deploy the application:

(Click to enlarge)

When you deploy a Role Instance you can also set the “Upgrade Domain”. Placing Roles on separate Upgrade Domains means that you have a continuous service whenever you upgrade (more on upgrades in another post) - the process looks like this for two Roles. This example covers the scenario for upgrade, so you have four roles total - One Web and one Worker running the "older" code, and one of each running the new code. In all those Roles you want at least two instances, and this example shows that you're covered for High Availability and upgrade paths:

The take-away is this - always plan for forward-facing Roles to have at least two copies. For Worker Roles that do background processing, there are ways to architect around this number, but it does affect the SLA if you have only one.

Java Resources for Windows Azure

BuckWoody — Tue, 13 Mar 2012 00:45:00 GMT

Windows Azure is a Platform as a Service – a PaaS – that runs code you write. That code doesn’t just mean the languages on the .NET platform – you can run code from multiple languages, including Java. In fact, you can develop for Windows and SQL Azure using not only Visual Studio but the Eclipse Integrated Development Environment (IDE) as well.

Although not an exhaustive list, here are several links that deal with Java and Windows Azure:

Resource	Link
Windows Azure Java Development Center	http://www.windowsazure.com/en-us/develop/java/
Java Development Guidance	http://msdn.microsoft.com/en-us/library/hh690943(VS.103).aspx
Running a Java Environment on Windows Azure	http://blogs.technet.com/b/port25/archive/2010/10/28/running-a-java-environment-on-windows-azure.aspx
Running a Java Environment on Windows Azure	http://blogs.technet.com/b/port25/archive/2010/10/28/running-a-java-environment-on-windows-azure.aspx
Run Java with Jetty in Windows Azure	http://blogs.msdn.com/b/dachou/archive/2010/03/21/run-java-with-jetty-in-windows-azure.aspx
Using the plugin for Eclipse	http://blogs.msdn.com/b/craig/archive/2011/03/22/new-plugin-for-eclipse-to-get-java-developers-off-the-ground-with-windows-azure.aspx
Run Java with GlassFish in Windows Azure	http://blogs.msdn.com/b/dachou/archive/2011/01/17/run-java-with-glassfish-in-windows-azure.aspx
Improving experience for Java developers with Windows Azure	http://blogs.msdn.com/b/interoperability/archive/2011/02/23/improving-experience-for-java-developers-with-windows-azure.aspx
Java Access to SQL Azure via the JDBC Driver for SQL Server	http://blogs.msdn.com/b/brian_swan/archive/2011/03/29/java-access-to-sql-azure-via-the-jdbc-driver-for-sql-server.aspx
How to Get Started with Java, Tomcat on Windows Azure	http://blogs.msdn.com/b/usisvde/archive/2011/03/04/how-to-get-started-with-java-tomcat-on-windows-azure.aspx
Deploying Java Applications in Azure	http://blogs.msdn.com/b/mariok/archive/2011/01/05/deploying-java-applications-in-azure.aspx
Using the Windows Azure Storage Explorer in Eclipse	http://blogs.msdn.com/b/brian_swan/archive/2011/01/11/using-the-windows-azure-storage-explorer-in-eclipse.aspx
Windows Azure Tomcat Solution Accelerator	http://archive.msdn.microsoft.com/winazuretomcat
Deploying a Java application to Windows Azure with Command-line Ant	http://java.interoperabilitybridges.com/articles/deploying-a-java-application-to-windows-azure-with-command-line-ant
Video: Open in the Cloud: Windows Azure and Java	http://channel9.msdn.com/Events/PDC/PDC10/CS10
AzureRunMe	http://azurerunme.codeplex.com/
Windows Azure SDK for Java	http://www.interoperabilitybridges.com/projects/windows-azure-sdk-for-java
AppFabric SDK for Java	http://www.interoperabilitybridges.com/projects/azure-java-sdk-for-net-services
Information Cards for Java	http://www.interoperabilitybridges.com/projects/information-card-for-java
Apache Stonehenge	http://www.interoperabilitybridges.com/projects/apache-stonehenge
Channel 9 Case Study on Java and Windows Azure	http://www.microsoft.com/casestudies/Windows-Azure/Gigaspaces/Solution-Provider-Streamlines-Java-Application-Deployment-in-the-Cloud/400000000081

Windows Azure Use Case: Web Applications

BuckWoody — Mon, 14 Feb 2011 17:22:42 GMT

This is one in a series of posts on when and where to use a distributed architecture design in your organization's computing needs. You can find the main post here: http://blogs.msdn.com/b/buckwoody/archive/2011/01/18/windows-azure-and-sql-azure-use-cases.aspx

Description:

Many applications have a requirement to be located outside of the organization’s internal infrastructure control. For instance, the company website for a brick-and-mortar retail company may want to post not only static but interactive content to be available to their external customers, and not want the customers to have access inside the organization’s firewall.

There are also cases of pure web applications used for a great many of the internal functions of the business. This allows for remote workers, shared customer/employee workloads and data and other advantages. Some firms choose to host these web servers internally, others choose to contract out the infrastructure to an “ASP” (Application Service Provider) or an Infrastructure as a Service (IaaS) company.

In any case, the design of these applications often resembles the following:

In this design, a server (or perhaps more than one) hosts the presentation function (http or https) access to the application, and this same system may hold the computational aspects of the program. Authorization and Access is controlled programmatically, or is more open if this is a customer-facing application. Storage is either placed on the same or other servers, hosted within an RDBMS or NoSQL database, or a combination of the options, all coded into the application.

High-Availability within this scenario is often the responsibility of the architects of the application, and by purchasing more hosting resources which must be built, licensed and configured, and manually added as demand requires, although some IaaS providers have a partially automatic method to add nodes for scale-out, if the architecture of the application supports it. Disaster Recovery is the responsibility of the system architect as well.

Implementation:

In a Windows Azure Platform as a Service (PaaS) environment, many of these architectural considerations are designed into the system.

The Azure “Fabric” (not to be confused with the Azure implementation of Application Fabric - more on that in a moment) is designed to provide scalability. Compute resources can be added and removed programmatically based on any number of factors. Balancers at the request-level of the Fabric automatically route http and https requests. The fabric also provides High-Availability for storage and other components. Disaster recovery is a shared responsibility between the facilities (which have the ability to restore in case of catastrophic failure) and your code, which should build in recovery.

In a Windows Azure-based web application, you have the ability to separate out the various functions and components. Presentation can be coded for multiple platforms like smart phones, tablets and PC’s, while the computation can be a single entity shared between them. This makes the applications more resilient and more object-oriented, and lends itself to a SOA or Distributed Computing architecture.

It is true that you could code up a similar set of functionality in a traditional web-farm, but the difference here is that the components are built into the very design of the architecture. The API’s and DLL’s you call in a Windows Azure code base contains components as first-class citizens. For instance, if you need storage, it is simply called within the application as an object. Computation has multiple options and the ability to scale linearly.

You also gain another component that you would either have to write or bolt-in to a typical web-farm: the Application Fabric. This Windows Azure component provides communication between applications or even to on-premise systems. It provides authorization in either person-based or claims-based perspectives.

SQL Azure provides relational storage as another option, and can also be used or accessed from on-premise systems. It should be noted that you can use all or some of these components individually.

Resources:

Design Strategies for Scalable Active Server Applications - http://msdn.microsoft.com/en-us/library/ms972349.aspx

Physical Tiers and Deployment - http://msdn.microsoft.com/en-us/library/ee658120.aspx