So you are deploying your application on Windows Azure cloud platform. One of the key features of a cloud platform like Azure is the ability to consume your compute resources with a utility model. Pay for only what is used, whether storage space, compute power, or amount of data transferred. Dynamic allocation of more space or bandwidth is built-in to Azure, but with respect to compute power, Windows Azure allows you to issue scale up or scale-down commands relatively easily. However, deciding when to do so can be a challenging task. This blog entry describes a service AzureWatch and how it can dynamically scale Windows Azure applications.
Part One - Introduction
At its core, AzureWatch aggregates and analyzes performance counters, queue lengths, and other metrics and matches that data against user-defined rules. When a rule produces a "hit", a scaling action or a notification occurs. You will need an account to install and use AzureWatch. Follow this link to fill out a simple registration form. After registration, download link for Windows-based configuration utility will be provided.
AzureWatch currently ships in two flavors: desktop edition and server-side edition. Server-side AzureWatch will monitor and auto-scale your Azure applications from its cloud-based servers. Desktop edition requires a special AzureWatch Monitoring agent to be installed on your premises. In desktop-edition the agent is responsible for gathering metrics and initiating scaling events.
Part Two - Start Control Panel
After installation is complete, start AzureWatch ControlPanel and login with your newly created account. You will be presented with a wizard to enter your Azure connection information.
Subscription ID can be found on your Windows Azure developer portal. If you do not already have the X.509 certificate, AzureWatch can create one for you. Follow the hyperlink on the wizard to get detailed instructions on creation certificates. It is a good idea to visit AzureWatch page to understand how your certificates and storage keys are kept secure.
After entering your account SubscriptionID and specifying a valid X.509 certificate, press Connect to Azure. You will be presented with a list of storage accounts. Storage account that is monitored by your Diagnostics Monitor is required.
On the next wizard page you can validate default settings for such things as throttle times, notification email, etc.
After the connection wizard is completed, AzureWatch will figure out what services, deployments and roles are present. For each role found, you will be offered a chance to create simple predefined rules.
The few sample rules offered are simple rules that rely upon basic metrics. We will come back to these rules in a short while. For now, wizards need to be completed.
Part Three - First time in Control Panel
After wizards complete, you are presented with a dashboard screen. It likely contains empty historical charts since no data has been collected so far. Navigation Explorer on the left shows various parameters that can be customized, while Instructions tab on the right shows context-sensitive instructions.
It is a good idea to visit the the Rules section to see the rules that have been defined by the wizard. Two sample rules should be present and can be edited by double-clicking on each. Rule Edit screen is simple yet powerful. You can specify what formula needs to be evaluated, what happens when the evaluation returns TRUE, and what time of day should evaluation be restricted to. To make formula entry easier, a list of already defined aggregated metrics is provided. Hovering over the formula box will display allowed operands.
One last place to visit before starting the monitoring process is the screen that contains safety limits for the number of instances that AzureWatch can scale up to or down to. By clicking on the appropriate Role name in the navigation explorer, you will be presented with a chance to modify these boundaries.
This is it. If you are ready, press "Publish Changes" button. Provided your AzureWatch Monitor service is running, it will pick up these configuration settings in the next iteration of its internal loop and instruct Azure Diagnostics Manager to start capturing the metrics required for formulas to work. Windows Azure will need a few minutes to instruct your instances to start capturing those metrics afterwards, and then a few minutes more before these metrics will be transferred to your storage. Thus, give AzureWatch at least 5-10 minutes before expecting to see anything on the Dashboard screen.
Part Four - A few tips and tricks
Some things to keep in mind while using AzureWatch
If you just started using AzureWatch and have not accumulated enough metric data, evaluation of your rules may be suspect as your aggregations will lack sufficient data. It maybe prudent to disable scaling inside Rules in the beginning so that your scaling actions do not trigger unexpectedly.
Metric transfer occurs only when Monitor is running. If you stopped Monitor service for an hour and then restarted it, it does not "go back" and send the missing hour's worth of metrics to AzureWatch.
When deploying new packages into Azure, you must use do it thru the same storage account that is specified in your DiagnosticsConnectionString and in AzureWatch System Settings. Failure to do this, will result in incomplete or incorrect metrics.
AzureWatch will always instruct your instances to capture metrics that are defined in the Raw Metrics screen. You do not need to do anything special with existing or newly started instances. It may be worthwhile, however, to visit the System Settings screen to further configure how metric enforcement and gathering works.
AzureWatch will send a notification when it scales your instances up or down. In it, it will provide values for all the aggregated metrics it knows about to help you understand why the scaling event occurred.
Locally installed AzureWatch components automatically self-update whenever a new version is released.