Coding Stories VII - Add, Subtract the same value

Looking over an open source library I found the following code:

interval void SomeMethodName(FooIncoming that)
if (that.numAnswers > 0)  
{
  SupportClass.IListSupport.AddAll(this.answers, this.numAnswers, (IList) ((ArrayList) that.answers).GetRange(0, that.numAnswers - 0));
  this.numAnswers += that.numAnswers;
}
if (that.numAuthorities > 0)
{
  SupportClass.IListSupport.AddAll(this.answers, this.numAnswers + this.numAuthorities, (IList) ((ArrayList) that.answers).GetRange(that.numAnswers, that.numAnswers + that.numAuthorities - that.numAnswers));
  this.numAuthorities += that.numAuthorities;
}
if (that.numAdditionals > 0)
{
  SupportClass.ICollectionSupport.AddAll(this.answers, (IList) ((ArrayList) that.answers).GetRange(that.numAnswers + that.numAuthorities, that.numAnswers + that.numAuthorities + that.numAdditionals - (that.numAnswers + that.numAuthorities)));
  this.numAdditionals += that.numAdditionals;
}
...
}

What I loved in this code was:

that.numAnswers – 0
that.numAnswers + that.numAuthorities - that.numAnswers
that.numAnswers + that.numAuthorities + that.numAdditionals - (that.numAnswers + that.numAuthorities)

I don’t understand why a developer would make something like this. Any number subtracted with 0 will have the same value like before. Also if you add a number and after that you subtract that same value you will get the original value.
The code would be equivalent with:

that.numAnswers
that.numAuthorities
that.numAdditionals

The second thing that I noticed is the ‘that’ argument. I’m not a fan of this kind of names. Maybe a name like ‘incoming’ or something similar would be better.

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Azure and IP Persistence - VM,Web/Worker Roles

If you already worked with Windows Azure, especially with worker roles, web roles or VM I suppose that you noticed that Azure don’t guaranty a static IP of this machines. Because of this it is not recommended to access or connect different Azure resources based on the IP (internal IP).
But in the same time, there are moments when the IP is persisted. For example when you restart the resource. In this blog post I will try to explain when the IP of the resources will not change and will remain the same after different actions.

Case: Upgrade
Let’s suppose that our resource is restarted after an update. In this case the original IP of it will be persisted.
Example:
Before:
VM_IN_0 – 10.0.0.10
VM_IN_1 – 10.0.0.11 (restarted)
After:
VM_IN_0 – 10.0.0.10
VM_IN_1 – 10.0.0.11

Case: Hardware fail
When we have a resource that I take down because of different situations (for example hardware fail) the original IP of the machine will be persisted after the instance is re-deployed. Even if the instance is moved on a different physical device.
Example:
Before:
VM_IN_0 – 10.0.0.10
VM_IN_1 – 10.0.0.11 (hardware fail)
After:
VM_IN_0 – 10.0.0.10
VM_IN_1 – 10.0.0.11

Case: Resource reboot
In the moment when a resource is rebooted the original IP will be persisted.
Example:
Before:
VM_IN_0 – 10.0.0.10
VM_IN_1 – 10.0.0.11 (reboot)
After:
VM_IN_0 – 10.0.0.10
VM_IN_1 – 10.0.0.11

Case: Scale up with a new image
When we need to scale up, allocating a new image of our resource a new IP will be allocated to this resource. The existing images will remain with the same IP as before.
Example:
Before:
VM_IN_0 – 10.0.0.10
VM_IN_1 – 10.0.0.11
After:
VM_IN_0 – 10.0.0.10
VM_IN_1 – 10.0.0.11
VM_IN_2 – 10.0.0.11

Case: Scale up after a scale down
After a scale up and a scale down, the next operation of scale up will not create a new image of the resource with the same IP as last time when we scale up.
Example:
Before:
VM_IN_0 – 10.0.0.10
VM_IN_1 – 10.0.0.11
Scale up:
VM_IN_0 – 10.0.0.10
VM_IN_1 – 10.0.0.11
VM_IN_1 – 10.0.0.12
Scale down:
VM_IN_0 – 10.0.0.10
VM_IN_1 – 10.0.0.11
After (scale up second time):
VM_IN_0 – 10.0.0.10
VM_IN_1 – 10.0.0.11
VM_IN_2 – 10.0.0.13

Case: Resource is de-allocated (stop de-allocate)
When we have a resource that is de-allocated we cannot assume that the current IPs will be persisted until the resource will be allocated again. Allocating the resource again will use different IPs
Example:
Before:
VM_IN_0 – 10.0.0.10
VM_IN_1 – 10.0.0.11
De-allocate
After (allocate resource again):
VM_IN_0 – 10.0.0.12
VM_IN_1 – 10.0.0.13

If we have situations when the IP of the resource is the same, there is another story with MAC address. Don’t assume that if the IP will be the same, than the MAC address will persist also. For example for the hardware fail case, the MAC address will change because another VM will be used.

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Traffic Manager Overview

Starting from today we have a mechanism that give us the possibility to control the traffic that comes to our Azure services. The name of this service is Traffic Manager.
What does this means?

Performance Load Balancing
Well, the simplest scenario is when we have a service running on different data centers. In this case we want to be able to redirect users to the closest data centers. We could have a service that identifies the location of the user and based on this redirect him to a specific data center. This problem is resolved by Traffic Manager Service. Using the client IP, this service will identify the location of the client and will redirect him to the closest data center (the one that have the lowest latency).
To be able to monitor the performance of each endpoint you will need to specify a relative path to the resource that is monitored. The monitor part is pretty simple, the latency time of each endpoint resource is measure every 30 seconds. When one of the request exceed 10 seconds or the return request code is different than 200 for more than 4 times in a row the endpoint will be considered down.

Failover Load Balancing
Another scenario that is cover by Traffic Manager is the case when one of our services from a data center is down. In this case the Traffic Manager will be able to detect the failover of the service and redirect the traffic to another data center. In this way all the traffic will be redirect to a backup service. We can define the order of the endpoints. This means that if the endpoint one will be down, the Traffic Manager will try to redirect the traffic to the second endpoint. If the second endpoint is down, the traffic will be redirect to the 3rd one and so on.
The performance Load Balancing also monitors the status of the endpoint and will not redirect traffic to an endpoint that is down.

Round Robin Load Balancing
This is the classic case of load balancing. In this case we have 2 or more endpoints available. The first client is redirected to the first endpoint, the second client to the second one and so on. This is a simple and very efficient way to make load balancing.
Also in this case, the Traffic Manager Monitoring component will redirect traffic to the endpoints that are up and running.

A normal question is when does the Traffic Manager appear on the requested map. For example if we have a domain foo.com and we will create a traffic manager domain named foo.trafficmanager.net. When a request will come to our website DNS name the request will be redirect to the foo.trafficmanager.net. Based on the policy that we use the traffic manager will redirect the client request to one of our endpoint.
Of course the latency of our system will increase at first request, but this value will be very low. In normal cases I would consider this value equal to zero and is not relevant for normal web applications.
Also, you should know that the resources of the endpoint that is used to check if the latency of the service needs to be over HTTP or HTTPS protocol. If your services works with different protocols that you need to add a HTTP or HTTPS resource – this can be a simple resource like a small file.
Another important thing to do after you configure the traffic manager is to update the DNS resource record to redirect the request from foo.com to foo.trafficmanager.com.
What do you think about this service? Do you think that you will use it in the near feature?

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Summer Codecamp at Cluj-Napoca (July 31)

At the end of this month Codecamp will organize a community event in Cluj-Napoca. This event will be dedicated to Team Foundation Server 2012, System Center Virtual Machine Manager 2012, Visual Studio 2013 and Cloud. With all this systems we will discover how to manage and write betters test (unit-test and load-tests).
Registration link: codecamp-cluj-iulie2013.eventbrite.com

Agenda (for Romanians):
18:15-18:30 - Sosirea participanților
18:30-19:30 - Managementul testelor cu Team Foundation Server 2012 si System Center Virtual Machine Manager 2012, Adrian Stoian
19:30-20:30 - Load Tests using Visual Studio 2013 and cloud, Radu Vunvulea

Special thanks for our sponsors:

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Subscription count - (Part 7) Testing the limits of Windows Azure Service Bus

Let’s talk about Windows Azure Service Bus and the numbers of subscriptions that a topic can have. I started to prepare a POC for a possible client and it is possible to end up with hundreds of subscriptions on each topic.
Looking over the documentation from MSDN, each topic supports 2000 subscriptions. I wanted to see what is happening with the latency of each subscription if we have over 1000 of them per topic.
To find an answer to my question, I started to write a worker role that:
Creates a new subscription
Sends a message to the topic
Receives a message using the first subscription
I measured how long it takes to send a message to a topic that has 1, 2, … , 2000 subscriptions. The same think I’ve done for the first subscription of the topic. I measured how long it takes to read a message from it when we have 1,2, … , 200 subscriptions.
The code is extremely simple but the results are very interesting.
The first diagram shows how long the send and receive commands took. The blue color is for the send request to the topic and the orange one is for receive command for the first subscription of the topic. The AX represent the number of subscriptions per topic and the OY represent how long a command took (in milliseconds).

As you can see, the command latency doesn’t increase too much. Even for 2000 subscriptions the latency is under 100 milliseconds.
The next diagram show the average latency when we have 500, 1000, 1500 and 2000 subscriptions. Based on this result we observe that the latency increases with a factor under 1.5X.

We can say that we can use this service in our business scenarios for 2000 subscribers without a problem. The latency increases only with a factor that is under 1.5X. We could have a problem if the latency would increase with a factor of 10X or 100X. But we are in a safe zone.
It seems that Service Bus is a real cloud service that scales and works excellent.

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Visual Studio 2012 - Strange behavior durring the commit

Based on TFS and local machine configuration, when we make a check-in we can set a task associate with the changeset to Resolve status. There are times when you cannot change a task status to Resolve, for example different policy on TFS machine. If you are using Visual Studio 2008 or Visual Studio 2010, everything will be away – an error message will be displayed that notified you that the commit ended without success.
When working with Visual Studio 2012 you will discover that even if an error is displayed during the check-in, the changeset will be pushed to the source control without having a task associate to it. You will receive the TF237124 error, but only after the commit is pushed to source control. This will happen even if on the TFS you enforce a rule that allow to commit only if a task is specified.
I hate this behavior, because a commit is made to source control even if an error appears.
To be able to assign a task to the changeset, you will need to open the task in TFS or in the browser, navigate to ALL LINKS tabs and link the changeset to the task (you will need to know the changeset number).
If you want to change the default behavior and not to mark the task as resolve in the TFS, you will need to set to the false value the following key:

// Visual Studio 2010
[HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\10.0\TeamFoundation\SourceControl\Behavior]
"ResolveAsDefaultCheckinAction"="False"
//Visual Studio 2012
[HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\11.0\TeamFoundation\SourceControl\Behavior]
"ResolveAsDefaultCheckinAction"="False"

The problem with a check-in that is made even if an errors appears I expect to be solved in the near future. Is not acceptable this behavior.

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Today Software Magazine - Number 13 was published

This week the 13th number of Today Software Magazine was publish. In this number of the magazine a lot of interesting subject were discussed, starting from HTML 5, to lean software development and functional programming.
In the current number of TSM I wrote the 3rd part of the article that discuss about Hadoop, especially from the environment, costs and tools that can be used in combination with it.
You can find this new number of Today Software Magazine here: http://www.todaysoftmag.com/tsm/ro/13

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Remote debug of an application that is on Windows Azure using VPN

One cool thing that I like when working with Azure is the way how you can do remotely debug. In a classic system is not very easily to do something like this. Azure facilitate this using Visual Studio and attached to process mechanism.
Theoretically you should not need to do remote debug, but in practice you need to do this from time to time.
To be able to do something like this you will need to create a virtual network. Using the virtual network you will be able to establish a VPN connection between the cloud machines (network) and you. Using this feature you can do more complicated stuff, for example integrate your cloud network with the one from your premise, but we don’t needs something like this if we want remote debugging.
Creating the virtual network is pretty simple. You need to go to New-> Network -> Virtual Network and create a new one. For this purpose you don’t need to make any kind of custom configurations. Don’t forget to select your affinity group – this should represent the cloud machines that you want to access remotely using VPN.
After this step you should create a custom certificate on your machine and upload to the certificates tab of your private network.
Now we are ready for the last step. Download the VPN configuration from the dashboard tab and run it. From now, you will be connect to your private network using the VPN connection. Based on the machine name you can connect to any machine or …
you can do remote debug of your application very easily. Using Visual Studio you can attach to any process of your machines and do real time debugging.
Until now I didn’t needed this feature, but it is pretty cool how easily you can do something like this. No custom configuration, no custom tools, no IT department from the on premise network.

Helpful link: http://www.windowsazure.com/en-us/manage/services/networking/cross-premises-connectivity/#CreateVN

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