Microsoft Azure Reviews

We live in dynamic times. Buzzwords such as cloud computing, elastic scale, reliability and their synonyms are taking more and more space in our daily life. People (developers) want to move to the cloud. They are often confused by all the new terms. In this part 1 of [we-will-see-at-the-end-how-many] articles I will try to explain with non-geeky words the Windows Azure terms.

First of all, what is Cloud Computing before all? This is when Computing power (namely CPU, RAM, Storage, Networking) is delivered as a service via a network (usually internet), and not as a product (a server that we buy).

Cloud computing is a marketing term for technologies that provide computation, software, data access, and storage services that do not require end-user knowledge of the physical location and configuration of the system that delivers the services. A parallel to this concept can be drawn with the electricity grid, wherein end-users consume power without needing to understand the component devices or infrastructure required to provide the service.

So what is Windows Azure? Is it the new server operating system from Microsoft? Is it the new hosting solution? Is it the new workstation OS? Well, Windows Azure is the Microsoft’s Cloud Computing platform. It delivers various cloud services. Compute, Database, Storage, CDN, Caching, Access Control to name few.

Next part of the article will be focusing on Windows Azure Compute services.

Windows Azure Guest OS? When we talk about cloud computing, inevitably we talk about virtualization. Virtualization at very big degree. And when we talk about virtualization, we have a Host OS and Guest OS. When we talk about Windows Azure OS, we talk about Windows Azure Guest OS. This is the operating system that is installed on the Virtual Machines that run in the cloud. Windows Azure Guest OS has 2 families – OS Family 1 and OS Family 2. Windows Azure Guest OS Family 1 is based on Windows Server 2008 SP 1 x64, and Family 2 is based on Windows Server 2008 R2. All and any guest OS is 64 bits. You can get the full list of Windows Azure Guest OS here.

Windows Azure Cloud Service, or Hosted Service. The Hosted Service is the essence of your Cloud application:

A hosted service in Windows Azure consists of an application that is designed to run in the hosted service and XML configuration files that define how the hosted service should run

A hosted service can have one or more Roles.

Now it comes to the Roles. Our cloud application can be a Web Based application, or a background processing application, or some legacy application which is hard to migrate. Or mix of the three. In order to make things easy for developers, Microsoft has defined 3 distinguished types of “Roles” – Web Role, Worker Role and VM Role. You can read a bit more for the “Role”s here. But the main idea is that a Role defines an application living environment. The Role contains all the code that our application consists of. It defines the environment where our application will live – how many CPUs will be installed; the amount of RAM installed; volume of local storages; will it be a full IIS or a background worker; will it be Windows Azure Guest OS 1.x or 2.x; will it has open ports for communication with outer world (i.e. tcp port 80 for Web Role); will it has some internal TCP ports open for internal communication between roles; what certificates will the environment has; environment variables; etc.

The Role is like a template for our cloud application. When we configure our Cloud Service (or Azure Hosted Service), we set the number of instances involved for each Role.

Instance is a single Virtual Machine (VM), which has all the properties defined by the Role and has our application code deployed. When I mentioned that the Role defines the number of CPUs, RAM, local storage, I was referring the configuration for each VM where our code will be deployed. There are couple (5) of predefined VM configuration which we can use:

More information on Virtual Machine sizes can be found here.

And here comes the beauty of the Cloud. We code once. We set the overall parameters once. And we deploy once! If it comes that we need more servers – we just set the number of instances for our role. We do it live. There is no downtime. Windows Azure automatically will launch as many VMs as we requested. Will configure them for our application and will deploy our code in each and every one of them and will finally join them to the cluster of our highly available and reliable cloud application. When we don’t need (let’s say) 10 servers anymore, then we can easily instruct Windows Azure that we only need 2 from now on and that’s it. The cloud will automatically shutdown 8 servers and remove them, so we won’t be paying any more extra money.

It is important to note, though, that the Role defines the size of the VM for all the Instances of it. We cannot have instances of same Role but different VM size. This is by design. If we defined our Role to use Extra Large VM, then all the instances we have will be running on that size of VM.

Key takeaways

I hope that this article helped you understand couple of basic terms about Windows Azure. You shall be able to confidently answer the following questions:

• What is Windows Azure ?
• What is Windows Azure Hosted Service (or just Hosted Service)?
• What is a Role?
• What is a Role Instance (or just Instance)?

Following the first two posts of the series “Windows Azure Basics” (general terms, networking) here comes another one. Interestingly enough, I find that a lot of people are confused what exactly is the compute emulator and what are these strange IP Addresses and port numbers that we see in the browser when launching a local deployment.

If you haven’t read the Windows Azure Basics – part 2 Networking, I strongly advise you to do so, as rest of current post assumes you are well familiar with real Azure deployment networking components.

A real world Windows Azure deployment has following important components:

• Public facing IP Address (VIP)
• Load Balancer (LB) with Round Robin routing algorithm
• Number of Virtual Machines (VM) representing each instance of each role, each with its own internal IP address (DIP – Direct IP Address)
• Open ports on the VIP
• Open ports on each VM

In order to provide developers with as close to real world as possible, a compute emulator needs to simulate all of these components. So let's take a look what happens when we launch locally a Cloud Service (a.k.a. Hosted Service).

VIP Address

The VIP address for our cloud service will be 127.0.0.1. That is the public IP Address (VIP) of the service, via which all requests to the service shall be routed.

Load Balancer

Next thing to simulate is the Azure Load Balancer. There is a small software emulated Load Balancer, part of the Compute Emulator. You will not see it, you are not able to configure it, but you must be aware of its presence.  It binds to the VIP (127.0.0.1). Now the trickiest thing is to find the appropriate ports to bind. You can configure different Endpoint for each of your roles. Only the Input Endpoints are exposed to the world, so only these will be bound to the local VIP (127.0.0.1). If you have a web role, the default web port is 80. However, very often this socket (127.0.0.1:80) is already occupied on a typical web development machine. So, the compute emulator tries to bind to the next available port, which is 81. In most of the cases port 81 will be free, so the "public" address for viewing/debugging will be https://127.0.0.1:81/. If port 81 is also occupied, compute emulator will try the next one – 82, and so on, until it successfully binds to the socket (127.0.0.1:XX). So when we launch a cloud service project with a web role we will very often see browser opening this wired address (https://127.0.0.1:81). The process is same for all Input Endpoints of the cloud service. Remember, the Input endpoints are unique per service, so an Input Endpoint cannot be shared by more than one Role within the same cloud service.

Now that we have the load balancer launched and bound to the correct sockets, let's see how the Compute Emulator emulated multiple instances of a Role.

Web Role

Web Roles are web applications that run within IIS. For the web roles, compute emulator uses IIS Express (and can be configured to use full IIS if it is installed on the developer machine).  Compute Emulator will create a dedicated virtual IP Address on the local machine for each instance of a role. These are the DIPs of the web role. A local DIP looks something like 127.255.0.0. Each local "instance" then gets the next IP address (i.e. 127.255.0.0, 127.255.0.1, 127.255.0.2 and so on). It is interesting that the IP Addresses begin at 0 (127.255.0.0). Then it will create a separate web site in IIS Express (local IIS) binding it to the created Virtual IP Address and port 82. The emulated load balancer will then use round robin to route all requests coming to 127.0.0.1:81 to these virtual IP Addresses.

Note: You will not see the DIP virtual address when you run ipconfig command.

Here is how does my IIS Express look like when I have my cloud service launched locally:

Worker role

This one is easier. The DIP Addressing is the same, however the compute emulator does not need IIS (neither IIS Express). It just launches the worker role code in separate processes, one for each instance of the worker role.

The emulator UI

When you launch a local deployment, Compute Emulator and Storage Emulator are launched. You can bring the Compute Emulator UI by right clicking on the small azure colored windows icon in the tray area:

For purpose of this post I've created a sample Cloud Service with a Web Role (2 instances) and a Worker Role (3 instances). Here is the Compute Emulator UI for my service. And if I click on "Service Details" I will see the "public" addresses for my service:

Known issues

One very common issue is the so-called port walking. As I already described, the compute emulator tries to bind to the requested port. If that port isn't available, it tries next one and so on. This behavior is known as "port walking". Under certain conditions we may see port walking even between consequent runs of same service – i.e. the first run compute emulator binds to 127.0.0.1:81, the next run it binds to 127.0.0.1:82. The reasons vary, but the obvious one is "port is busy by another process". Sometimes the Windows OS does not free up the port fast enough, so port 81 seems busy to the compute emulator. It then goes for the next port. So, don't be surprised, if you see different ports when debugging your cloud service. It is normal.

Another issue is that sometimes browser launches the DIP Address (https://127.255.0.X:82/) instead the VIP one (https://127.0.0.1:81/). I haven't been able to find a pattern for that behavior, but if you see a DIP when you debug your web roles, switch manually to the VIP. It is important to always use our service via the VIP address, because this way we also test out application cloud readiness (distributing calls amongst all instances, instead of just one). If the problem persists, try restarting Visual Studio, Compute Emulator or the computer itself. If issue still persists, open a question at StackOverflow or the MSDN Forum describing the exact configuration you have, ideally providing a Visual Studio solution that constantly reproduces the problem. I will also be interested to see the constant repeatable issue.

Tip for the post: If you want to change the development VIP address ranges (so that it does not use 127.0.0.1) you can check out the following file:

%ProgramFiles%\Microsoft SDKs\Windows Azure\Emulator\devfabric\DevFC.exe.config

DevFC stands for "Development Fabric Controller". But, please be careful with what you do with this file. Always make a backup of the original configuration before you change any setting!

Happy Azure coding!

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