Wednesday, September 23, 2009

Unit Tests for registry read fails in Visual Studio on 64 bit machines

My my my...
A hotch potch of Windows Server 2008 and Visual Studio 2008 on a 64 bit machine killed my 3-4 hours today...

So here's the deal
I've a method in one of my dlls which reads a certain value from a sub key of HKEY_LOCAL_MACHINE\SOFTWARE Then i wrote a unit test to test this method. Turns out it fails to read the Registry. I was amazed because registry entry did exist in the registry. After struggling for about an hour or so i decided to write a console application to test the method. And the method worked :O. So now i was in a situation where a method works from the console application while fails from a unit test.

I thought that its a permissions issue so i gave full trust to both the assemblies i.e. unit test assembly and the assembly i was testing. Even that didn't help.
Looking at the task manager of the system i saw that the unit tests run under a process call VSTestHost.exe. So next i tried to give full trust to this exe however that's not possible since it is a win32 exe.

A relook at the Task Manager showed me that the process runs under VSTestHost.exe*32 means a 32 bit process running on a 64 bit OS. Nothing suspicious about it in the first look. However if you look at the nodes below HKEY_LOCAL_MACHINE\SOFTWARE in the registry you see a node called Wow6432Node and that made me think. After some search i figured out that if you run a 32 bit process on a 64 bit machine and try to read the subkeys of HKEY_LOCAL_MACHINE\SOFTWARE The registry reads are actually directed to HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node. So i made an entry in this node and it worked.

Lesson :- Be careful while working with registries if you depend on registry for your program to work.

Happy coding :)


Thursday, September 17, 2009

Making SQL Server Replication work on Network Service Account

This is one of the topics i have been working on since last few days. There's not much information available on the web on how to do that so i decided to log it in this blog.

Problem Statement :-
Setup a SQL Server replication while running the SQL Server in "Network Service" Account.

Normal Convention :-
Most local SMEs i spoke to suggested that it is not possible to setup replication between SQL Servers using the Network Service account and suggested that i use the domain account instead. However the problem with that solution is that domain account password expires in some time and then we may even get a production downtime.

Proper Solution :-
The SQL Service like any other windows service can be run using Local Service, Network Service or a Domain Account credentials. Now if you want to setup a replication Local Service account is of no use since that is an account which has no identity over the network. Domain account is not ideal since passwords have to be changed at regular intervals resulting in downtime as well as maintainance costs. So Network Service account is the ideal way to go. This account presents the machine identity over the network.
So if we want to setup replication using this account the machine identities should have access to databases. We can create a security group in active directory and add all the machines which want to talk to each other in replication should be added to this group. Then give the permission to this security group on all the databases.
This way when the replication service on one machine sends the replication related instructions to another machine it presents the machine credential which has the permissions on the database, the replication has no security related problems.
so to summarize
1) Make sure that all the SQL Service and SQL Agent Service is running using Network Service credential
2) Create a security group in the domain and add all the SQL machines which would be part of replication to this group
3) Give this security group appropriate permissions on all the databases which would be part of replication.

Happy coding...


Monday, September 7, 2009

Resource Oriented Architecture - Part 2 (Statelessness)

The idea of writing a web service was that you should have a contract to work against. The policy, address etc. to invoke the implementation of this contract can be figured out at runtime. A component on remote machine will process my input and get back to me with some output based on the design time contract which i programmed against.

Now this works great once i take a look at the tools which are available to me as off today ... I've a WCF framework based on which i can define my operation contracts, message contracts, data contracts etc. in the code and the security policy, binding and address on which i want to expose my contract can be decided at the time of deployment in a configuration file. The best part is that in most cases i do not even need to care that i am writing a service which would be used from a remote client.. since even the things likes session management etc. can easily be handled by the framework. I feel like i am almost doing OOPS based programming. However if i do use the Session in my service an additional overhead has been added to the service infrastructure of maintaining this session. Which means that i put the scalability challenges in my code. Because to support Session i've to use Session Affinity or and Out of Process Session Management both of which are not very bright ideas for scaling out the application.

The World Wide Web is a very scalable architecture and one of the reasons for that is its statelessness.
Let's try to understand what statelessness means for an application....
In any application we write there are 2 states i.e. state of the client and the state of the resource which the client is asking for. When we walk about statelessness we mean that the server should only be concerned about the state of the resource it is serving to the client. It should not be concerned about the state of the client. e.g. when i type a url in my browser google returns me the result for my query ROA starting with result no. 80 i.e. page 9. It doesn't care whether i clicked on last 8 pages or not because that is the state of the client. The state of the resource is present on the server and is being served no matter what is the state of the client querying for it is.

While designing a resource oriented application we should be very clear in defining what is the resource that we're exposing, what is the state of the resource and what can be classified as client state. Then we should ensure that the client state is maintained by the client and sent to the server when needed in some form (most as part of URL. Wait till my post on addressability and uniform interface).


Resource Oriented Architecture - Part 1

Defining the Agenda :-

If i look at it SOA has been one of the biggest BUZZWords I've seen since i came into programming world. I came from a Object Oriented Background and WebServices or RPC Style web services looked like a perfect way to build a SOA based application to me however off late i am getting a feel that writing web services the way we do today is probably not the perfect way to make applications.

In this 5 part series i am going to talk about the various tenets of Resource Oriented Architecture and figure out what next steps i can take to understand or define a Resource Oriented Architecture for a business process......


Microsoft TR9 @ Seattle

I attended Microsoft TechReady 9 in Seattle in July and have been away from this space ever since :). TR9 was one of the great experiences i had in Microsoft in my 1 year @ Microsoft.
For someone who doesn't know what TechReady is, its basically biggest Microsoft Services event where Microsofties from the field get together to share the learnings and to get a gist of what's coming next from the product groups. Now i can't share the details of what i saw there in terms of upcoming products because of obvious reasons however as i see it .... the future looks bright.
I also got an oppurtunity to present on Developing Secure RESTful services using Microsoft WCF 3.5.
It was a great experience and the attendee party in The Commons @ Redmond was great :)
All in all nice experience and i got a new topic to work on i.e. ROA and RESTful services....

Stay tuned as i am now working on ROA so you would see some posts coming soon and one might be out in a couple of hours or even less ....