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How are customer service and technical support?

Which solution did I use previously and why did I switch?

How was the initial setup?

What's my experience with pricing, setup cost, and licensing?

Which other solutions did I evaluate?

What other advice do I have?

I was recently asked whether I do have some cheat-sheet for migrating applications to Windows Azure. The truth is that everything is in my head and I usually go with “it should work” – quickly build, pack and deploy. Then troubleshoot the issues. However there are certain rules that must be obeyed before making any attempt to port to Windows Azure. Here I will try to outline some.

Disclaimer

What I describe here is absolutely my sole opinion, based on my experience. You are free to follow these instructions at your own risk. I describe key points in migrating an application to the Windows Azure Platform-as-a-Service offering – the regular Cloud Services with Web and/or Worker Roles. This article is not intended for migrations to Infrastructure Services (or Windows Azure Virtual Machines).

Database

If you work with Microsoft SQL Server it shall be relatively easy to go. Just download, install and run against your local database the SQL Azure Migration Wizard. It is The tool that will migrate your database or will point you to features you are using that are not compatible with SQL Azure. The tool is regularly updated (latest version is from a week before I write this blog entry!).

Migrating schema and data is one side of the things. The other side of Database migration is in your code – how you use the Database. For instance SQL Azure does not accept “USE [DATABASE_NAME]” statement. This means you cannot change database context on the fly. You can only establish connection to a specific database. And once the connection is established, you can work only in the context of that database. Another limitation, which comes as consequence of the first one is that 4-part names are not supported. Meaning that all your statements must refer to database objects omitting database name:

[schema_name].[table_name].[column_name],

instead of

[database_name].[schema_name].[table_name].[column_name].

Another issue you might face is the lack of support for SQLCLR. I once worked with a customer who has developed a .NET Assembly and installed it in their SQL Server to have some useful helpful functions. Well, this will not work on SQL Azure.

Last, but not least is that you (1) shall never expect SQL Azure to perform better, or even equal to your local Database installation and (2) you have to be prepared for so called transient errors in SQL Azure and handle them properly. You better get to know the Performance Guidelines and Limitations for Windows Azure SQL Database.

Codebase

Logging

When we target own server (that includes co-locate/virtual/shared/etc.) we usually use local file system (or local database?) to write logs. Owning a server makes diagnostics and tracing super easy. This is not really the case when you move to Windows Azure. There is a feature of Windows Azure Diagnostics Agent to transfer your logs to a blob storage, which will let you just move the code without changes. However I do challenge you to rethink your logging techniques. First of all I would encourage you to log almost everything, of course using different logging levels which you can adjust runtime. Pay special attention to the Windows Azure Diagnostics and don’t forget – you can still write your own logs, but why not throwing some useful log information to System.Diagnostics.Trace.

Local file system

This is though one and almost always requires code changes and even architecting some parts of the application. When going into the cloud, especially the Platform-as-a-Service one, do not use local file system for anything else, but a temporary storage and static content that is part of your deployment package. Everything else should go to a blob storage. And there are many great articles on how to use blob storage here.

Now you will probably say “Well, yeah, but when I put everything into a blob storage isn’t it vendor-lock-in?” And I will reply – depending on how you implement this! Yes, I already mentioned it will certainly require code change and, if you want to make it the best way and avoid vendor-lock-it, it will probably also require architecture change for how your code works with files. And by the way, file system is also “vendor-lock-in”, isn’t it?

Authentication / Authorization

It will not be me if I don’t plug-in here. Your application will typically use Forms Authentication. When you redesign your app anyway I highly encourage you rethink your auth/autz system and take a look into Claims! I have number of posts on Claims based authentication and Azure ACS(Introduction to Claims, Securing ASMX web services with SWT and claims,  Identity Federation and Sign-out, Federated authentication – mobile login page for Microsoft Account (live ID), Online Identity Management via Azure ACS, Creating Custom Login page for federated authentication with Azure ACS,  Unified identity for web apps – the easy way). And couple of blogs I would recommend you to follow in this direction:

• Dominic Baier: http://leastprivilege.com/
• Vittorio Bertocci: http://www.cloudidentity.com/blog/

Other considerations

To the moment I cant dive deeper in the Azure ocean of knowledge I have to pull out something really important that fits all types of applications. If it happens, I will update the content. Things like COM/COM+/GDI+/Server Components/Local Reports – everything should work in a regular WebRole/WorkerRole environment. Where you also have full control for manipulating the operating system! Windows Azure Web Sites is far more restrictive (to date) in terms of what you can execute there and to what part of the operating system you have access.

Here is something for you think on: I worked out with a customer who was building SPA Application to run in Windows Azure. They have designed a bottleneck for scaling in their core. The system manipulates some files. It is designed to keep object graphs of those files in-memory. It is also designed in a way that end-user may upload as many files as day want during the course of their interaction with the system. And the back-end keeps a single object graph for all the files user submitted in-memory. This object graph cannot be serialized. Here is the situation:

In Windows Azure we (usually, and to comply with SLA) have at least 2 instances of our server. These instances are load balanced using round-robin algorithm. The end user comes to our application, logs-in and uploads a file. Works, works, works – every request is routed to a different server. Now user uploads new file, and again, and again … each request still goes to a different server.

And here is the question:

What happens when the server side code wants to keep a single object graph of all files uploaded by the end user?

The solution: I leave it to your brains!

Conclusion

Having in mind the above mentioned key points in moving application to Windows Azure, I highly encourage you to play around and test. I might update that blog post if something rather important comes out from the deep ocean of Azure knowledge I have. But for the moment, these are the most important check-points for your app.

If you have questions – you are more than welcome to comment!

• LB – Load Balancer. It is the Windows Azure software Load Balancer, which routes the Internet traffic to and from your hosted service;
• VIP – virtual IP address. This is the internet facing public IPv4 (currently) network address for your hosted service. You have to pay attention to it, as you only have one single internet facing IP address per hosted service;
• DIP – direct IP address. This is an internal subnet IPv4 network address that each single instance of your roles has. You have one of these DIPs for every single instance, and there is only one per instance. This IP address in internal subnet and cannot be used to directly access a specific instance from outside the Windows Azure hosted service. You can, however use this address for internal communication between instances of your roles within the whole Windows Azure deployment (hosted service)t;

1. The LB (Load Balancer) will not route any Internet traffic to the instances of your roles;
2. The Windows Firewall of all your instances is set to default block everything (Effectively blocking even communication between different instances in a single deployment);

Side note: you maybe already noticed that I am using “instances” more often then “roles”. I hope that you’ve read my first post and already know the difference. The key difference is that the instance is the actual VM (Virtual Machine) where your code lives, while the Role only defines the “footprint” for what to be instantiated on the Virtual Machine.

• You can have a maximum of 25 Endpoints per hosted service (Input + Internal);
• You define your endpoints by a Role! Meaning that two different roles cannot share a single Endpoint;
• All your Endpoints within a Hosted Service must be unique. Meaning that you cannot have an Input Endpoint (i.e. “EndpointWeb") serving HTTP protocol on port 80 for one Role and have another Input Endpoint (i.e. EndpointWebMVC) serving again HTTP protocol on port 80 for another Role. Here I stress that we define Endpoints at Role level, so every instance of this role will have the endpoints defined;

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!

What is most valuable?

What needs improvement?

For how long have I used the solution?

What do I think about the stability of the solution?

What do I think about the scalability of the solution?

How are customer service and support?

How was the initial setup?

What about the implementation team?

What's my experience with pricing, setup cost, and licensing?

What other advice do I have?

Which deployment model are you using for this solution?

If public cloud, private cloud, or hybrid cloud, which cloud provider do you use?

What is our primary use case?

What is most valuable?

What needs improvement?

For how long have I used the solution?

What do I think about the stability of the solution?

What do I think about the scalability of the solution?

How are customer service and support?

How was the initial setup?

What about the implementation team?

What's my experience with pricing, setup cost, and licensing?

Which other solutions did I evaluate?

What other advice do I have?

If public cloud, private cloud, or hybrid cloud, which cloud provider do you use?