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In   Marlabs’ Guide to Improving Operational Agility and Efficiency Involved in Load Balancing and Scaling using Windows Azure – Part 1 and Part 2 , we  looked at Autoscaling, and also introduced the Windows Azure Autoscaling Application Block (WASABi). Now let us see how to  Edit the Autoscaling Application Block Configuration.

You can add ad edit the Autoscaling application block configuration using Enterprise Library Configuration tool. To install the Enterprise Library Configuration tool, do the following steps

1. In Visual Studio, on the Tools menu, click Extension Manager.

2. In the Extension Manager dialog, click Online Gallery, and then in the Search Online Gallery box, type Enterprise Library Config.

3. Make sure that you can see version 5.0.505 of the EnterpriseLibrary.Config package. Then click the Download button.

4. Read the license and then click Install.

5. Click the Restart Now button to restart Visual Studio and complete the installation.

To edit the Autoscaling application block configuration using Enterprise Library Configuration tool, right click on the app.config file in the project that will be hosting the block and click Edit configuration file.

In the Enterprise Library Configuration tool, open the Blocks menu, and then click Add Autoscaling Settings.

The enterprise library configuration tool allows editing Autoscaling settings, Rule store information and the Service information store. The Rule Store settings contain the storage information about Rules configuration file and the Service Information Store settings contain the storage information about Service configuration file. Typically, if you host the Autoscaling Application Block in a worker role, you will store the data points, rule definitions, and service information in Windows Azure storage.

Author Rule Configuration File

The rule configuration file contains the rules that will be used for the scaler to scale up and scale down the hosted service. There are two types of rules available in the Autoscaling Application Block – constraint rules and reactive rules. Constraint rules are associated with a time table and reactive rules are associated with KPI and conditions. The below code block shows the sample rule configuration which contains both constraint rules and reactive rules.

The above rule configuration contains two constraint rules – a default rule and a rule for peak business time on every Fridays. The rank specified in the rule configuration is just a priority for each role. The ‘utcOffset’ value is using to convert the configured local time to UTC time using by the Windows Azure. The reactive rules contain the rules for KPI based on the CPU utilization.

Author Service Configuration File

The service configuration file contains the information for Windows Azure subscriptions and hosted service(s) to monitoring for auto scaling. This tells the Scaler that which hosted service(s) should monitor. The below code blocks show the sample service configuration file.

Quick Steps to Add and Use Autoscaling Application Block

The following are the major quick steps to add and use Autoscaling Application Block

1. Add a reference to Autoscaling Application Block in host application.

2. Instantiates the Autoscaler class and call its start method for monitoring.

3. Edit app.config file of the host application using Enterprise Library configuration tool.

4. Configure the Autoscaling settings.

5.Configure the Rule Store settings to specify the storage information of Rules configuration file.

6. Configure the Service Information Store to specify the storage information of Service information configuration file.

7. Add Rules configuration XML file to specify the rules and conditions for scaling.

8. Add Service information XML file to specify Windows Azure subscription and hosted services to monitoring the Autoscaling Application Block.

 
Windows Azure Compute Resources to Host Autoscaling Application Block

The following compute resources are the essential components to host Autoscaling block

1. Windows Azure hosted service for Worker Role to host Autoscaling block.

2. BLOB storage account for store rule configuration and service information configuration.

Conclusion

Windows Azure is Microsoft’s offering for Cloud computing to help customers to build and deploy applications on a Pay-per-use basis and providing on-demand scalability. This allows the customers to fully focus on their applications rather than managing IT infrastructure. The Windows Azure Autoscaling Application Block lets the Windows Azure customers to take full advantage of scalability offerings provided by Windows Azure. This enables the customers to reduce number of management overheads involved load balancing and scaling which will improve the business agility and can also reduce cost and time.

In the first part of  Marlabs’ Guide to Improving Operational Agility and Efficiency Involved in Load Balancing and Scaling using Windows Azure we examined Autoscaling, its business need, and benefits. Now let us look at the Windows Azure Autoscaling Application Block (WASABi)

Windows Azure Autoscaling Application Block (WASABi)

The Windows Azure Autoscaling Application Block (WASABi) lets the cloud developers to add and manage automatic scaling behavior to Windows Azure applications that provides all the functionality needed to define and monitor autoscaling behavior in a Windows Azure application or a group of Windows Azure applications. The Windows Azure Autoscaling Application Block is a part of the Microsoft Enterprise Library provided by the Microsoft patterns & practices team. The Windows Azure Autoscaling Application Block can automatically scale Windows Azure applications based on the rules defined in configuration files specifically for the hosted Windows Azure application. The block will read the rules and monitor Windows Azure applications and scale-up or scale-down the applications based on the rules. The Autoscaling Application Block can be hosted on a Windows Azure worker role application or in an on-premises application. The Enterprise Library provides a GUI based configuration tool that can be used for edit configuration settings for the Autoscaling Application Block.

Major functionalities of Windows Azure

The following are the key functionalities of Autoscaling Application Bloc:

• Instance Scaling – The Autoscaling Application Block varies the number of role instances in order to accommodate variations in the load on the application. Instance scaling actions can span multiple host services/subscriptions.
• Throttling – Instead of spinning off new instances, the block limits or disables certain expensive operations in your application when the load is above certain thresholds.
• Notifying – Instead of performing instance scaling or throttling, the user may elect to simply receive notifications about the load situations with no automatic scaling taking place.
• Custom action – We can build extensions using the extensibility features provided by Autoscaling Application Block.

Adding Autoscaling Application Block to Host Application

The Autoscaling Application Block is available as a NuGet package .The following steps will add the Autoscaling Application Block onto your host application.
1. Add a reference to the Autoscaling Application Block assembly. In Microsoft Visual Studio, right-click your project node in Solution Explorer, and then click Manage NuGet Packages.
2. Click the Online button, and then in the Search Online box, type WASABi.
3. Click the Install button for the Enterprise Library 5.0 – Windows Azure Autoscaling Application Block – Beta package.
4. Read and accept the license terms for the packages listed.

The NuGet package will add the all necessary assemblies and references to your project that you need to use the Autoscaling Application Block. The NuGet package will also add the XML schema files for the autoscaling rule definitions and autoscaling service information.

Hosting the Autoscaling Application Block in a Windows Azure Worker Role

Autoscaling Application Block needs a host to run. The Autoscaling Application Block can be hosted on a Windows Azure worker role application or in an on-premises application. The following step by step instructions will help you to host the Autoscaling Application Block onto Windows Azure Worker Role.

Instantiate and Run the Scaler

The following steps will instantiate and run the Autoscaling Application Block in a Windows Azure Worker Role.

Import Namespaces

Import the following namespaces to the Worker Role class

using Microsoft.Practices.EnterpriseLibrary.Common.Configuration;

using Microsoft.Practices.EnterpriseLibrary.WindowsAzure.Autoscaling;

Resolve an Instance of Autoscaler Class

The Autoscaler class is the main entry point for the Autoscaling Application Block from your host application. The following code block instantiates the Autoscaler class and call its start method for monitoring the Autoscaling behavior.

When you call the Start method of the Autoscaler class, the block will look for rule and service information, and will start to monitor hosted services and will perform the auto scaling based on the rules defined in the rule store.

To be continued . . .

Read the Marlabs White Paper on Improving Operational Agility and Efficiency Involved in Load Balancing and Scaling using Windows Azure.