When developing enterprise applications you need to consider the networking environment they need to access. Applications that only use internal enterprise networks present challenges as you have to play in their sandbox, after all they own the network. Many of those concerns can be overcome by contacting the right people. It would seem that applications which access the broader Internet would be easier to deal with given the perception of openness on the Internet and the standardization of specifications like HTTP/1.1.
There has been no shortage of stories about governments' intrusive role in the Internet around the globe like China's Great Firewall or the Egyption ISP shutown. Even in the US there are stories of the government restricting access to content, implementing cyber-threat countermeasures and trying to maintain Net Neutrality. Although, Net Neutrality really has less to do with government and more to do with corporations trying to restrict and monetize access to the Internet. However, my recent experience shows some Internet Service Providers (ISP) have already started.
While developing an enterprise application I needed to indicate to the user whether or not the computer was on the internal enterprise network. To do this I decided to have the application perform a web request to another resource (i.e.. computer) that I knew was always available only on the client's network. It did exactly what I wanted to in the client's office. However, when I brought my computer home to test the application I was shocked to find that the application showed that it successfully connected to the server.
I consider the Internet to be anything outside of my house, including my Internet Service Provider (ISP). As such I expect the Internet to be open and follow the HTTP/1.1 specification. However my ISP, Verizon FiOS, rolled out a "feature" a couple years ago that breaks the HTTP/1.1 specification. The specification states that if a requested resource cannot be found then a return code of "404 - Not Found" should be sent back to the requestor. When I used Fiddler to trace the return codes I noticed that the response ended up being "200 - OK" meaning the server was found. However, as you can see in Figure 1 the initial resource I was looking for wasn't found, but instead of 404 return code, my ISP returned a 302 (which should be a 307, but that's another issue). The 302 return code tells the requestor that the requested resource has moved to a new location and the requestor should look there instead. The problem with this is that resource hasn't moved, it is simply not available because it doesn't exist on the Internet.
| Result | Protocol | Host | URL | Body |
| 302 | HTTP | my application FQDN | / | 0 |
| 302 | HTTP | wwwwz.websearch.verizon.net | /wwwwz.websearch.verizon.net/search?qo=my application FQDN... | 0 |
| 307 | HTTP | goto.searchassist.com | /goto.searchassist.com/find?p=paxfire&s=my application FQDN... | 0 |
| 200 | HTTP | find.searchassist.com | /find.searchassist.com/landing.jsf?p=cnksver&q=my application FQDN... | 48,875 |
Apparently Verizon starting doing these redirects to help users when they mistype a URL and then extended it to redirect 404 responses. I can see using this to reduce overall costs by cutting the number of support calls. However, I think this was first and foremost an opportunity to generate ad revenue. Whatever the reason, it breaks the way the open Internet is supposed to work in my opinion, so I decided to turn off Verizon's redirect "feature".
Microsoft released a new version of IIS called IIS Express 7.5. It allows you to run a scaled down version of IIS 7.5 on Windows XP and greater. For example, IIS 5.1 ships with Windows XP Pro, but not Windows XP Home. Yet you can still run IIS 7.5 on Windows XP Home. However, please note their may be some features that do work in earlier version of Windows due the changes in architecture.
IIS Express 7.5 does not run as a service and does not require administrative privileges to run. The short term goal was to make it work with WebMatrix, but the long term plans are to replace the ASP.Net development web server (i.e. Cassini) with this product for use within Visual Studio 2010. If you want to try it out, but you don't want to use WebMatrix, you can try using IIS Express 7.5 in Visual Studio 2010 RTM with some effort or you can download the beta of Service Pack 1 for Visual Studio. The product can also be used without Visual Studio or WebMatrix, but You must have the .Net framework 4.0 installed prior to installing IIS Express 7.5.
If you plan to use Visual Studio 2010 RTM, then I recommend creating a shortcut to "C:\Program Files\IIS Express\iisexpress.exe" or "C:\Program Files (x86)\IIS Express\iisexpress" if you are running a 64-bit edition of Windows. Once you establish your site information (see these instructions) you can make changes to the shortcut to align with your project in Visual Studio 2010.
There has been good news for developers this year on the cloud computing front. There are freely available compute clouds offering a fairly robust environment, although I would caution enterprise software developers to not use corporate assets (e.g. code and data) when trying them out. This is especially true for systems that have to provide compliance to standards like PCI. Those private enterprise systems would be better off leveraging a service like HP's Cloud Start. For developers that just want to get their feet wet, here is a list of free environments:
Microsoft has allowed MSDN Subscribers to leverage Windows Azure platform for free.1,2 Those details are as follows:
For those that don’t have an MSDN subscription, Microsoft announced a free trial offer earlier this year as well that is good until June 30, 2011.1 Those details are as follows:
Starting November 1, 2010, new Amazon customers will be able to take advantage of a free EC2 instance for one year.1 In addition they will be able to leverage free usage tiers of S3, Elastic Block Storage, Elastic Load Balancing and AWS data transfer. So the free details are as follows:
1 - credit card must be used to sign up and charges will be incurred if the free limits are exceeded
2 - must have an existing Premium, Ultimate or BizSpark MSDN subscription
Back in November of 2008, the FCC approved the unlicensed use of white space, provided users of this space abided by two rules. First, they were not permitted to transmit a signal if any legacy wireless microphone had been used in the space in the past 60 seconds. In addition, the user needed to check an FCC White Space database to determine which channels were available at a given location.
Earlier this week the FCC introduced some new constraints on the use of white space in the TV station broadcast spectrum. The order still requires the database lookup, but it no longer calls for spectrum sensing for wireless microphones and instead reserves two vacant channels on the UHF band for limited local use. For others that have a need for more channels the FCC recommends registering with the TV band database.
The use of these frequencies tends to be very limited in major metropolitan areas where there are virtually no available white spaces. However in rural America there are opportunities galore. The primary talk around use of the frequencies has been "White-Fi", which is simply a wireless network operating on the 6 Mhz white space channels. Microsoft has been a pioneer in this space, as is evident in the prototype "white-fi" network on their Redmond campus. The IEEE 802.22 working group has also been working on techniques to use the spaces for Wireless Regional Area Networks.
Time will tell if white space broadband makes its way through rural America, or if it will go the way of Broadband over Powerlines. Although the town of Claudville, VA has already been successful in adopting the technology.
Greg was one of the first bloggers to bring the idea of CQRS (Command Query Responsibility Segregation) into the .Net world, so I think it is safe to say he knows what CQRS is. He recently posted a blog on a how CQRS is essentially the same as the MVC UI pattern. He makes this comparison based on the fact that one would use a "command model" and a "query model" in an application.
However, I completely disagree with his relation between a code-based implementation pattern and a data store location. The thing I don’t like about Greg's comparison is that I don't have to use CQRS in MVC and I don't have to implement CQRS using MVC, so I think his statement is going to cause confusion. Therefore saying they are sort of the same doesn’t work for me. Furthermore, I still hold the CQRS is nothing more but a new term to talk about caching.
The controller is responsible for separating the view and the model. To that end, one "could" use the controller in an MVC implementation to know which model to read from and which model to write to, although there is no reason you couldn’t have more than two models. The controller would more then likely expose a CQS-style interface and it would probably be a great way to implement CQRS.
If I did implement CQRS using MVC then I would probably use a cached abstraction over my model that would look something like this:
public class DataStruct {
public int key { get; set; }
public string stuff { get; set; }
}
public interface IModel {
DataStruct GetData(int key);
void UpdateData(DataStruct data);
void InsertData(DataStruct data);
}
public class CachedModel : IModel
{
private readonly Cache _cache = HttpContext.Current.Cache;
private readonly IModel _model;
public CachedModel(IModel model) {
this._model = model;
}
public DataStruct GetData(int key) {
return this._cache.Get(GetKey(key)) as DataStruct ?? GetDataFromStore(key);
}
private DataStruct GetDataFromStore(int key) {
DataStruct data = this._model.GetData(key);
this._cache.Add(GetKey(key), data, null, DateTime.Now.AddSeconds(30),
TimeSpan.Zero, CacheItemPriority.Default, null);
return data;
}
public void UpdateData(DataStruct data) {
this._model.UpdateData(data);
this._cache.Remove(GetKey(data.key));
}
public void InsertData(DataStruct data) {
this._model.InsertData(data);
}
private string GetKey(int key) {
return string.Format("dataKey:{0}", key);
}
}
public class Model : IModel {
private readonly ModelEntities _context;
public Model(ModelEntities context) {
this._context = context;
}
public DataStruct GetData(int key) {
return this._context.DataStructs.FirstOrDefault(d => d.key == key);
}
public void InsertData(DataStruct data) {
this._context.AddToDataStructs(data);
