How to Scale Web Sites
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You use the Windows Azure Management Portal to scale your web sites, and to specify whether you want to run them in Free web site mode, Shared web site mode or Reserved web site mode.
Table of Contents
Free Web Site Mode
When a web site is first created it runs in Free web site mode, meaning that it shares available compute resources with other subscribers that are also running web sites in Free or Shared web site mode.
A single instance of a web site configured to run in Free mode will provide somewhat limited performance when compared to other configurations but should still provide sufficient performance to complete development tasks or proof of concept work.
If a web site that is configured to run in a single instance using Free web site mode is put into production, the resources available to the web site may prove to be inadequate as the average number of client requests increases over time. If the CPU time quota is exceeded for the web site, all web sites in the same subscription are stopped (Web site instances normally unload after going idle for 20 minutes). The web sites are started again at the next quota interval.
Before putting a web site into production, estimate the load that the web site will be expected to handle and consider scaling up / scaling out the web site by changing configuration options available on the web site's Scale management page.
Scale options applied to a web site are also applied to all web sites that meet the following conditions:
- Are configured to run in Shared or Reserved web site mode.
- Exist in the same region as the web site for which scale options are modified.
For this reason it is recommended that you configure any "proof of concept” web sites to run in Free web site mode or create the web sites in a different region than web sites you plan to scale up or scale out.
Shared Web Site Mode
A web site that is configured as or updated to Shared mode uses a low-cost scaling mode that provides more performance than Free mode. Changing to Shared mode is easily done in the Scale tab of the management portal. These changes take only seconds to apply, and do not require code to be changed or the application to be redeployed.
A web site in Shared mode is deployed in the same multi-tenant environment as one in Free mode, but has no quotas or upper limit to the amount of bandwidth it can serve. The first 5 GB of bandwidth served on a Shared web site is free; subsequent bandwidth is charged at the standard "pay-as-you-go" rate for outbound bandwidth.
A web site running in Shared mode also now supports the ability to receive mapping for multiple custom DNS domain names, using both CNAME and A-records. Using A-records allows web sites to be accessed using only the domain name (e.g. http://microsoft.com in addition to http://www.microsoft.com). In the future, SNI-based SSL will also be available for web sites running in Shared mode.
Reserved Web Site Mode
A web site that is configured as Reserved will provide more consistent performance than a web site that is configured as Free or Shared.
When you configure a web site as Reserved, you specify the size of the web site (Small, Medium or Large). A web site that is configured with a larger Reserved Instance Size will perform better under load.
You also specify a value for Reserved Instance Count (from 1 to 3). Increasing the value for Reserved Instance Count will provide fault tolerance and improved performance through scale out.
Before switching a web site from Free web site mode to Reserved web site mode you must first remove spending caps in place for your Web Site subscription.
How to: Change Scale Options for a Web Site
A web site that is configured to run in Free or Shared web site mode has access to the resources associated with an ExtraSmall Virtual Machine Size described in the table at How to: Configure Virtual Machine Sizes.
To change scale options for a web site, in the Management Portal open the web site's Scale management page to configure the following scaling options:
Web Site Mode - Set to Free by default. When you change the Web Site Mode from Free or Shared to Reserved, the web site is scaled up to run in a Small compute instance on a single dedicated core with access to additional memory, disk space and bandwidth. For more information, see How to: Configure Virtual Machine Sizes.
Reserved Instance Size - Provides options for additional scale up of a web site running in Reserved web site mode. If Reserved Instance Size is changed from Small to Medium or Large, the web site will run in a compute instance of corresponding size with access to associated resources for each size. For more information, see How to: Configure Virtual Machine Sizes.
Reserved/Shared Instance Count - Increase this value to provide fault tolerance and improved performance through scale out by running additional web site instances.
Note that as you increase the value for Shared Instance Count you also increase the possibility of exceeding the resources allocated to each Web Site subscription for running web sites in Shared web site mode. The resources allocated for this purpose are evaluated on a resource usage per day basis. For more information about resource usage quotas see How to Monitor Web Sites.