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configuration. When this process is completed, the new node is ready to service requests to your application. Much of the image deployment can be completed before the node is needed, cutting down on the time it can take to start a new instance and add it to your service. Each server can contain several VMs. This allows for the optimal use of computing resources and the flexibility to move instances around as needed. As a second or third virtual server is added, it might use the base OS VHD that has already been downloaded u or it can download a different base OS VHD based on its needs. This second machine then follows the same process of downloading the application VHD, booting up, and enrolling into the cloud. All these steps are coordinated by the FC and are usually accomplished in a few minutes.

If the key to the automation of Azure is Hyper-V, then the base VM images and their management are the cornerstone. Images are centrally created, also in an automated fashion, and stored in a library, ready to be deployed by the FC as needed. A variety of images are managed, allowing for the smallest footprint each role might need. If a role doesn t need IIS, then there s an image that doesn t have IIS installed. This is an effort to shrink the size and runtime footprint of the image, but also to reduce any possible attack surfaces or patching opportunities. All images are deployed using an Xcopy deployment model. This model keeps deployment simple. If the FC relied on complex scripts and tools, then it would never truly know what the state of each server would be and it would take a lot longer to deploy an instance. Again, diversity is the devil in this environment. This same approach is used when deploying patches. When the OS needs to be patched, Microsoft doesn t download and execute the patch locally as you might on your workstation at home. Doing so would lead to too much risk, having irregular results on some of the machines. Instead, the patch is applied to an image and the new image is stored in the library. The FC then plans a rollout of the upgrade, taking into account the layout of the cloud and the update domains defined by the various service models that are being managed. The updated image is copied in the background to all of the servers used by the service. After the files have been staged to the local disk, which can take some time, each update domain group is restarted in turn. In this way, the FC knows exactly what s on the server. The new image is merely wired up to the existing service bits that have already been copied locally. The old image is kept locally for a period of time as an escape hatch in case something goes wrong with the new image. If that happens, the server is reconfigured to use the old image and rebooted, according to the update domains in the service model. This process dramatically reduces the service window of the servers, increasing uptime and reducing the cost of maintenance on the cloud.

We ve covered how images are used to manage the environment. Now we re going to explain what you can see when you look inside a running role instance.

Your first experience with roles in Azure is likely to be with the web role. To help you develop your web applications more effectively, it s worth looking in more detail at the VM that your web role is hosted in. In this section, we ll look at the following items: The details of the VM The hosting process of your web role (WaWebHost) The RDAgent process