Session State with Windows Azure Caching Preview
July 3, 2012 4 Comments
I’m working on a project for a client and was asked to pull together a small demo using the new Windows Azure Caching preview. This is the “dedicated” or better yet, “self hosted” solution that’s currently available as a preview in the Windows Azure SDK 1.7, not the Caching Service that was made available early last year. So starting with a simple MVC 3 application, I set out to enable the new memory cache for session state. This is only step 1 and the next step is to add a custom cache based on the LocalStorage feature of Windows Azure Cloud Services.
Enabling the self-hosted, in-memory cache
After creating my template project, I started by following the MSDN documentation for enabling the cache co-hosted in my MVC 3 web role. I opened up the properties tab for the role (right-clicking on the role in the cloud service via the Solution Explorer) and moved to the Caching tab. I checked “Enable Caching” and set my cache to Co-located (it’s the default) and the size to 20% of the available memory.
Now because I want to use this for session state, I’m also going to change the Expiration Type for the default cache from “Absolute” to “Sliding”. In the current preview, we only have one eviction type, Least Recently Used (LRU) which will work just fine for our session demo. We save these changes and take a look at what’s happened with the role.
There are three changes that I could find:
- · A new module, Caching, is imported in the ServiceDefinition.csdef file
- · A new local resource “Microsoft.WindowsAzure.Plugins.Caching.FileStore” is declared
- · Four new configuration settings are added, all related to the cache: NamedCaches (a JSON list of named caches), LogLevel, CacheSizePercentage, and ConfigStoreConnectionString
Yeah PaaS! A few options clicked and the Windows Azure Fabric will handle spinning up the resources for me. I just have to make the changes to leverage this new resource. That’s right, now I need to setup my cache client.
Note: While you can rename the “default” cache by editing the cscfg file, the default will always exist. There’s currently no way I found to remove or rename it.
Client for Cache
I could configure the cache manually, but folks keep telling me to I need to learn this NuGet stuff. So lets do it with the NuGet packages instead. After a bit of fumbling to clean up a previously botched NuGet install fixed (Note: must be running VS at Admin to manage plug-ins), I right-clicked on my MVC 3 Webrole and selected “Manage NuGet Packages”, then following the great documentation at MSDN, searched for windowsazure.caching and installed the “Windows Azure Caching Preview” package.
This handles updating my project references for me, adding at least 5 of them that I saw at a quick glance, as well as updating the role’s configuration file (the web.config in my case) which I now need to update with the name of my role:
Now if you’re familiar with using caching in .NET, this is all I really need to do to start caching. But I want to take another step and change my MVC application so that it will use this new cache for session state. This is simply a matter of replacing the default provider “DefaultSesionProvider” in my web.config with the AppFabricCacheSessionStoreProvider. Below are both for reference:
Its important to note that I’ve set the cacheName attribute to match the name of the named cached I set up previously, in this case “default”. If you set up a different named cache, set the value appropriately or expect issues.
But we can’t stop there, we also need to update the sessionState node’s attributes, namely mode and customProvider as follows:
Of course, all this does nothing unless we have some code that shows the functionality at work. So let’s increment a user specific page view counter. First, I’m going to go into the home controller and add in some (admittedly ugly) code in the Index method:
The first section just sets up the session value and handles incrementing them. The second block pulls the value back out to be displayed. And then alter the associated Index.cshtml page to render the values back out. So just insert the following wherever you’d like it to go.
Now if we’ve done everything correctly, you’ll see the view count increment consistently regardless of which instance handles the request.
Now there’s some interesting stuff I’d love to dive into a bit more if I had time, but I don’t today. So instead, let’s just be happy with the fact that after more than 2 years, Windows Azure finally has “built in” session provider that is pretty darned good. I’m certain it still has its capacity limits (I haven’t tried testing to see how far it will go yet), but to have something this simple we can use for most projects is simply awesome. If you want my demo, you can snag it from here.
Oh, one last note. Since Windows Azure Caching does require Windows Azure Storage to maintain some information, don’t forget to update the connection string for it before you deploy to the cloud. If not, you’ll find instances may not start properly (not the best scenario admittedly). So be careful.
Until next time!