Efficient hosting of applications in a cloud requires continuous optimization of application availability. To meet increasing demand, you have to scale network resources upward. When demand subsides, you need to scale down to avoid the unnecessary cost of idle resources. To minimize the cost of running the application by deploying only as many instances as are necessary during any given period of time, you have to constantly monitor traffic. However, monitoring traffic manually is not a feasible option. For the application environment to be able to scale up or down rapidly, you need to automate the processes of monitoring traffic and of scaling resources up and down whenever necessary.
If your organization uses Citrix CloudPlatform to deploy and manage the cloud environment, a Citrix NetScaler appliance can automatically scale users' applications as needed. The CloudPlatform elastic load balancing feature includes a feature called AutoScale. A CloudPlatform user can use the AutoScale feature to specify thresholds for various conditions for automatically scaling the application fleet upward and downward. The scale-up and scale-down conditions can vary from simple use cases, such as a server's CPU usage, to complex use cases, such as a combination of a server's CPU usage and responsiveness. CloudPlatform, in turn, configures the NetScaler appliance to load balance traffic to the application virtual machines (VMs), monitor application thresholds and performance, and trigger scale-up and scale-down actions to add or remove VMs to or from the application fleet.
The CloudPlatform user performs all AutoScale configuration tasks by using the CloudPlatform user interface or APIs. The CloudPlatform user:
- Creates a load balancing rule, with the necessary load balancing algorithm and stickiness.
- Configures AutoScale parameters by specifying the application instance template, the minimum number of instances to maintain, the maximum number of instances permitted, scale-up and scale-down policies, and other information necessary for the functioning of the feature.
- Submits the configuration.
For information about configuring a load balancing rule and AutoScale, see Citrix CloudPlatform 3.0.5 (powered by Apache CloudStack) Administrator's Guide, at http://support.citrix.com/article/CTX134823.
When the CloudPlatform user completes the AutoScale configuration, CloudPlatform uses the NetScaler NITRO API to push all the necessary configuration commands to the NetScaler appliance. As the NetScaler administrator, you do not have to perform any tasks for configuring AutoScale on the NetScaler appliance. However, you might have to be aware of certain prerequisites, and you might have to troubleshoot the configuration if issues arise in the AutoScale configuration. To troubleshoot the configuration, you have to be aware of how CloudPlatform works and what configuration CloudPlatform pushes to the NetScaler appliance. You also need a working knowledge of how to troubleshoot issues on a NetScaler appliance.