I’ve been working on a free-to-play MMO Quinine For Sale, which has been “officially” live since last April, and things have been going well – a steady growth of players; the game itself has been well-received, and all the important graphs are “up and to the right.”  Part of my job involves detecting problems before they become serious and fixing problems when they inevitably do.  So, there are two questions.  “Is there a problem in the game?” “What is causing the problem?” 

When trying to debug something on our development and test clusters, typically you can tail log files.  We have a python script that can monitor the communication between various parts of the game and pretty-print it along with color to highlight “this is a problem!”  Attaching a debugger to a running process is also not uncommon.  However, looking at logs and bus traffic in realtime on a production environment gives you this neat “Matrix-y” experience.  Attaching a debugger to a production process (assuming you could, which you can’t) would get you smacked with a rolled-up newspaper.  “Bad Developer!  No treat!”  So, what can you do?

Monitoring

When you’ve got clusters full of machines, using Nagios to monitor things is an obvious solution.  Beyond making sure the power is on and other sysadmin things, we’ve written other checks to see if the login process is working, the parts are working together, and automating typical in-game functions.  For example, if nagios can’t successfully log into the game do basic game activity, then alerts happen.

Metrics for EVERYTHING

Anything that happens in game has metrics reporting tied to it, generating piles of data constantly.  We use Cacti to visualize game activity.  An example metric is concurrent users, or CCU.  We graph how many people are in the game over time, which when things are healthy should be a nice smooth curve climbing to peak game hours, then descending nicely through the night.

We can tell by sight if the game looks healthy or not – if the CCU graph is jaggy, has a sudden drop or spike, or drops to zero then we know that something is wrong.  Typically nagios alerts accompany the graphs, giving more data points on where to look.  But this has also pointed out areas where a nagios check was missing or wasn’t working as intended.

Log Files

When a player gets an error in game, the error dialog box gives them the opportunity to submit the error details back to us.  If we see a spike in user-reported errors through this or other customer service means, we know we have something of interest to look for. 

The game server components make use of log4j and similar logging frameworks.  Anything that you’d want to watch happening in game needs to be aggressively logged.  All components are configured so that operations can change the log level on the fly.  That’s still quite a bit of data across many machines though, so all that information is run through Splunk to be indexed and searchable.  This gives us a great tool for searching through log data, examining trends, or watching selected activity in real time.  Unfortunately it is very expensive so we are selective about the data that passes through it. 

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On the MMO Buy Prozac Without Prescription, I’m working on, we do quite a bit of service monitoring via jetty.  Things like having a URL that reports back version information for a component, or a page full of statistics showing recent activity, or a way to trigger a self-check in a component to determine if the component is sane and healthy or not.

For certain components we run multiple instances of the service on the same box.  In development environments, it’s a pretty small number of instances.  On a production environment it’s a much bigger number.  Typical stuff.  However Operations noticed that startup times for a server full of instances jumped from seconds to over 20 minutes when the number of instances was increased from 3 to 12.  Ouch.

So, something is blocking on startup.  After some digging, I came across this post explaining how jetty uses a secure random number generator for session ids, which is based on the pool of entropy generated by the system.  Sure enough…

$ cat /proc/sys/kernel/random/entropy_avail
128

(On development cluster machines that value is upwards of 3000)

Since we don’t care if the jetty session IDs are securely generated or not, switching the generator from secure to not-secure took us back to a few seconds to start up 20 instances.

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One of the long-standing MVC practices has been ‘Shun Magic Strings.’  For example, rather than specifying Controller/Action names in an ActionLink by string, we’ve always used an Expression<Action<TController>> instead to define the Controller class and Action method “in code.”  If the action changes in the future, this gives you somewhat better abilities to discover the problem sooner vs. later. 

MvcFutures includes a version of this idea, taken to the next level:  you provide the expression with the arguments you want passed to the action included – you don’t provide a 2nd anonymous type defining the arguments.  This gets rid of the somewhat confusing “null” arguments inside the expression, and just looks better overall.  Plus, if the arguments to the action change, you’ll get better warning of that as well.

<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
    <h2>Magic Strings are Evil</h2>
    <p>
        <%= Html.ActionLink<HomeController>(c => c.FavoriteNumber(16), "A Number") %>
        <%= Html.ActionLink<HomeController>(c => c.FavoriteNumber(32), "Another Number") %>
        <%= Html.ActionLink<HomeController>(c => c.FavoriteNumber(42), "Yet Another Number") %>        
    </p>
</asp:Content>

I like this method MUCH better. 

The implementation that makes this happen is in Microsoft.Web.Mvc.Internal.ExpressionHelper.  Which even though it’s in an “Internal” namespace, is neither marked Internal, Sealed, or otherwise made unavailable (hallelujah).  So you can use this trick for all sorts of things.

There is also a System.Web.Mvc.ExpressionHelper in the official MVC assembly, which is used to implement the smart Html.TextBoxFor(m => m.Property) functionality.  This class is also NOT internal, not sealed, not obfuscated and hidden away.  We’ve used it to extend the Html.[control]For() abilities to some other control types.  Very useful stuff.  Plus its just interesting code to read.

One potentially big caveat:  I’m told that the Html.ActionLink<TController>() methods don’t work if you’re using Areas in your MVC application.  I haven’t tried this myself, we aren’t using Areas in any of our MVC 2 applications yet.  That might be why this functionality is hidden in MvcFutures and not out with the rest of the smart expression code.

Problem: The raw bytes of the PDF are returned from SSRS by using the class Microsoft.SqlServer.ReportingServices2005.Execution.ReportExecutionService, via the Render() method.  This code works just fine in Dev, Test, and Stage environments – but in Production, without fail, this Render() method hangs and will never return back to the service process.

The Fix:  This functionality is a small bit in a much larger application, and even the PDF generation is a smallish piece of some larger responsibilities for the service.  So first, I want to isolate the behavior, and then duplicate it. 

I wrote a test windows service consisting of one project, that does one thing: when a timer fires, a hardcoded request to the production Reporting Services is made to get a PDF bytestream.  This service does what is expected in Dev and Stage, but when I tried to install it on Production:

An exception occurred while trying to find the installers in the C:\webreader\webreader.svc.exe assembly.
System.Reflection.ReflectionTypeLoadException: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.
Aborting installation for C:\webreader\webreader.svc.exe.

Can’t load a type?!  So I copy Microsoft.ReportViewer.Common.dll and Microsoft.ReportViewer.WebForms.dll into the program directory, and my test service installs and works perfectly.  Copying the same files into the production service’s directory also fixes the problem.

So, if your Reporting Services ASMX calls are hanging, try changing your references over to “Copy Local” and see what happens…

Why this is weird: If those DLLs were missing or corrupt, then why did the original App code load and run (and hang)?  I thought perhaps the wrong version was referenced in the GAC, but no there were NO Microsoft.ReportViewer.*.dll’s registered.  The service installer caught the missing types when the references were all in one assembly, but didn’t have any problems when the references were spread into a 2nd assembly. 

Just when I think “hey, maybe I’m getting a hang of this .NET stuff” a problem like this happens…

Minimum and Maximum Zoom

This part is easy – I added two properties, MinimumZoom and MaximumZoom, default them to double.MinValue and double.MaxValue, and some trivial code in DoZoom to keep the scale values in line:

   1: public PanAndZoomViewer() {

   2:   MaximumZoom = double.MaxValue;

   3:   MinimumZoom = double.MinValue;

   4: }

   5: public double MaximumZoom { get; set; }

   6: public double MinimumZoom { get; set; }

   7:  

   8: public void DoZoom(double deltaZoom, 

   9:                    Point mousePosition, 

  10:                    Point physicalPosition) {

  11:   // Keep Zoom within bounds declared by Minimum/MaximumZoom

  12:   double currentZoom = zoomTransform.ScaleX;

  13:   currentZoom *= deltaZoom;

  14:   if (currentZoom < MinimumZoom)

  15:     currentZoom = MinimumZoom;

  16:   else if (currentZoom > MaximumZoom)

  17:     currentZoom = MaximumZoom;

  18:   // do zoom animation stuff...

  19: }

Limiting Pan Transform

This required slightly more thought, and some graph paper.  Having a clue about how WPF deals with its coordinate systems would have been helpful too.  I have a Canvas as the Content of my PanAndZoomViewer.  No matter what panning & zooming happens, this Canvas will always have a fixed Height and Width.  The Origin in our setup is always going to be the upper left corner of the Canvas, and remember that in the coordinate system used by Windows, “up” and “left” from that point are negative values.  (The Y axis is the opposite of what you’d expect).  Here’s a lame Paint.NET picture to help you understand:

The Red View area is the part of the map canvas you’re zoomed into and viewing.  The blue area is the entire map.  I don’t want you to be able to move the Red rectangle beyond the boundaries of the Blue Rectangle, because instead of viewing the map you’d be viewing the dining room table, or the Red Rectangle would fall off the table onto the floor, or something.

Handling the Left and Top boundaries of the Blue Rectangle are easy enough, at any zoom level.  If you were to move the Red Rectangle to beyond either of those edges, then one or both of the values for (ToX, ToY) would be positive (past the Origin corner).  So we reset positive values back to zero and then animate to keep things nice and smooth.

Pan Right, Bottom

The other two edges are slightly less intuitive, at least to me.  Consider the Right edge of the Red Rectangle View: I don’t want this edge passing over the Blue Rectangle.  This puts a “maximum” value on the distance from the Left Edge of the Red Rectangle (at X = 0), and the Left Edge of the Blue Rectangle.  Except that this value would be negative being to the left of the origin, so it’s really a minimum.  (Trivial arithmetic, I know, and yet I still messed it up the first time.) 

So, the minimum allowed ToX value is content.Width - (content.Width * scale).  If you try to move the Red Rectangle farther away, we just snap it back to the edge.  Same thing with the minimum Y values.

The Result

The code to handle this looks something like this:

   1: private void control_MouseMove(object sender, MouseEventArgs e)

   2: {

   3:     if (!IsMouseCaptured)

   4:         return; // don't care.

   5:  

   6:     // if the mouse is captured then move the content by changing the translate transform.  

   7:     // use the Pan Animation to animate to the new location based on the delta between the 

   8:     // starting point of the mouse and the current point.

   9:     Point physicalPoint = e.GetPosition(this);

  10:  

  11:     // where you'd like to move the top left corner of the view to

  12:     double toX = physicalPoint.X - ScreenStartPoint.X + startOffset.X;

  13:     double toY = physicalPoint.Y - ScreenStartPoint.Y + startOffset.Y;

  14:     Console.WriteLine("You're attempting to move to " + toX + "," + toY);

  15:  

  16:     double scaleValue = zoomTransform.ScaleX;

  17:     var content = (FrameworkElement)Content;

  18:  

  19:     // minimum values we can shift the origin to - 

  20:     // maximum values is always 0 (we don't want the left side of the content

  21:     // ever being beyond the left part of the view

  22:     double minToX = content.Width - (content.Width * scaleValue);

  23:     double minToY = content.Height - (content.Height * scaleValue);

  24:  

  25:     // correct any invalid amounts:

  26:     if (toX > 0)

  27:         toX = 0;

  28:     else if (toX < minToX)

  29:         toX = minToX;

  30:  

  31:     if (toY > 0)

  32:         toY = 0;

  33:     else if (toY < minToY)

  34:         toY = minToY;

  35:  

  36:     translateTransform.BeginAnimation(TranslateTransform.XProperty, CreatePanAnimation(toX),

  37:                                       HandoffBehavior.Compose);

  38:     translateTransform.BeginAnimation(TranslateTransform.YProperty, CreatePanAnimation(toY),

  39:                                       HandoffBehavior.Compose);

  40: }

All The Source Code

I found how to fix your solution of the zoom example you put here ... It is necessary to animate the CenterX and CenterY properties of the scaling, not just the ScaleX and ScaleY properties. It is because after the animation ends, the values set by the animation take precendense of the regular properties of the transformation. With this fix it works fine, but only for the image size you used. It does not work with larger images, because there is no pan feature.

The bad news:  I’m writing this on a Windows box and support for some things is sketchy or just non-existent.  Also, using Python vs. this C library puts a big distance between “what you think is happening” and “what is happening,” so debugging leaves you wondering if the problem is your code, Eclipse somehow messing things up, Python, the Python bindings, somewhere within openCV, or just broken or incomplete support for Windows.

So imagine my confusion when this simple program:

import cv
img = cv.LoadImage("img.tif")

I mean, what’s simpler than just loading a file from disk?! 

I found many people reporting this error, but no solutions other than “The file or directory doesn’t exist or isn’t readable…”

So, after checking (and rechecking) that the file does indeed exist, and then after using the full path to the file and getting the same error, I tried to find where the error was originating through all these layers.

I tried opening the image file using PIL and then converting the image over to OpenCV format, which did not generate an error, except that the resulting image wouldn’t quite survive the process – so I guess that doesn’t count as “working.”  Displaying the image using Windows Photo Viewer worked fine.  Out of desperation I grabbed a random image off of the Internet and tried to open it with OpenCV --- and it worked.

Hmm, where did my original images come from?  I screen-grabbed them off of another application, and then to save time - rather than waiting for Gimp to open - I just used MSPAINT.EXE to … oh, damn.  “Short Cuts make for Long Journeys.”  The original file was corrupt, just enough so that openCV would be unable to load it, but not so much that other programs and libs couldn’t load “something.”

So, ignore the text of that error message and read it as “openCV, for some reason that it won’t describe, could not load your image.  Maybe the file is not there, or maybe you messed it up by being sloppy?” 

Re-capturing the image using Gimp and PNG fixed the problem.

Over time, the bandwidth problems were fixed, and as sometimes happens the WSUS server crumbled to dust.  For the most part nobody noticed – new servers and clients were not configured with the WSUS policy, downloading their hotfixes direct from Microsoft through plentiful bandwidth.  Unfortunately, older server and clients were left in the dark, sending cries out to a WSUS URL that will never respond...  oops

To Fix (and get your automatic updates to work again):

Delete the registry key at “HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate”.  For fun, restart the “Windows Update” service (not sure if this is necessary). 

I found this VBS file to be useful in figuring out if a server was still trying to use an old WSUS install, or if the problem was group-policy related. 

The tl;dr version

Azure involves a classic tradeoff: being able to scale very effectively and not having to make major capital investments, vs. having to pay more to your cloud computing environment for the convenience of it.  It’s suitable for some applications and businesses, but certainly not all.  To make the most of it, you should (or, must) architect your application around the whole cloud-notion to begin with.  How much, and how bad it’ll hurt, depends on platform and your application.

The Long Winded Version

Let’s say you’re a big online retailer, selling books online (as an example I just made up).    For 3 months of the year, your servers are completely slammed with orders – you need lots of bandwidth, lots of CPU, everything.  I’m talking about renting out a big data center for $BidMoney a month, hiring SysAdmins, NetAdmins, all of that.    The other 9 months of the year, its boring.  You could just have a server under your desk, and hire some high school kid to keep it running.

This is why Amazon’s EC2 was invented (and why Microsoft is competing with them with Azure).   Rather than buying racks of servers, hiring staff to keep it running, and so on - for stuff that you won’t need for most of the year, you deploy your application to Azure – when times are busy, you spool up additional servers easily.  When the rush is over, just throw those extra instances away.

Your startup get mentioned in the WSJ?  Add servers to deal with the traffic, so you don’t look stupid with “Server Unavailable” errors.  Any sort of business model that is built around ‘bursts’ makes a lot of sense for this.

The tradeoff:  Cost.  You pay for CPU time, storage space, transactions, bandwidth.  Each of these are really small numbers like “.15 / GB stored / month” and “.01 / 10k transactions” but they can add up quickly - a Death of a Thousand Cuts.  Plus, with EC2 and Azure, the CPU time is not “cpu time doing something useful,” it is “amount of hours the virtual server was running.”   So if your app spends most of its time doing nothing…

For a small app with little traffic, this could add up to 0s / month, instead of just paying $VeryLittle/month for really lousy shared hosting, or a little more for less-lousy virtual hosting.   And as I understand it, all of these services are “No Refunds” so if you get hit with a big wave of traffic, or forget to turn a server off when you were done with it, or whatever, … too bad, pay up! 

It’s not all bad though – Google App Engine is free for 500 MB of storage and 5 million page views, and when you’re ready for more you can set up a quota and daily budget so you don’t get any nasty surprises.  And while Azure is in CTP, its without charge (with a few modest quotas applied).  So, you can start writing your Facebook-killer app right now, and deal with the costs later :)

Application Design

With Google App Engine and Amazon EC2, and mostly with Microsoft Azure, you must design your applications with cloud operation up front.  It’s not exactly trivial to take an app written for a more traditional web server/database structure and deploy it to the cloud: you should be using the cloud’s data access APIs, not storing anything on the server itself, and have ways to get your data to and from the cloud (racking up transaction fees in the process).  And don’t forget that your data is out there in hostile territory – how are you going to keep it safe?  Plus your choice of cloud dictates what languages and platforms you can choose from.

I said “mostly” because with Azure you can pay a little extra to get access to “SQL Azure” if you need relational database storage.  Which I think is great, although you’d have to balance those costs against the effort of using a more transaction based storage model.

So there you go, a tiny bit of understanding packed into a dangerous form of leaping conclusions.  :)

I’m writing a very basic WebPart to get started with SharePoint – this web part will display a list of links to other applications that the user is authorized to use.  The source of this data (names, URLs, etc.) comes from an external-to-SharePoint system, accessed through another C# assembly.  Once the web part gets the data there is some more processing to be done – we need to do more than just blindly display a list of URLs.  Rather than get into details I’m just going to do some handwaving here and say that “if you have access to X, then {stuff happens}, or if you have access to Y then {other stuff happens}.”  You know, business logic, stuff that is good to test.

the first thing I need to do is get business logic out of the WebPart and into something that I can write without having to reset AppPools over and over, not to mention have some unit tests to verify I’m going in the right direction.  So, I created a standard application service class which has a dependency on the external authorization system, via constructor injection. 

public class AuthorizedAppsService : IAuthorizedAppsService
{
  private readonly ExternalAuthorizeService authService;

  public AuthorizedAppsService(
    ExternalAuthorizeService authService) 
  {
    this.authService = authService;
  }

  public AuthorizedApplications GetAuthorizedApplications(
                                  string userName)
  {
    var allApps = authService.AuthorizedApplications(userName);
    // business logic stuff happens here
    return thoseResultsWeJustFiguredOut;
  }
}

Next, I created a StructureMap Registry class to scan my assemblies, as well as adding in the details of how to create this external authorize service, using the typical method:

public class MyRegistry : Registry
{
  public MyRegistry()
  {
    Scan(scanner => {
      scanner.TheCallingAssembly();
      scanner.AssemblyContainingType(typeof(MyRegistry));
      scanner.WithDefaultConventions();
      });

    ForRequestedType<ExternalAuthorizeService>()
      .AsSingletons()
      .TheDefault.Is.ConstructedBy(c => Provider.GetService());

    // other dependency configuration...
  }
  public static void InitializeForSharepoint()
  {
    ObjectFactory.Initialize(init => init.AddRegistry<MyRegistry>());
    ObjectFactory.AssertConfigurationIsValid();
  }
}

And then, what remains is to have SharePoint call my StructureMap initialization when my SharePoint application starts up.  In an MVC or WebForms app, I’d just add code to the appropriate place in Global.asax.cs, but in SharePointLand, this is looked down on.  Instead, the preferred mechanism seems to be to use an HttpModule and a FeatureReceiver to plug the Module into the app’s web.config.

public class MyStartupModule : IHttpModule
{
  public void Init(HttpApplication context)
  {
        ConfigureOtherStuff();
        MyRegistry.InitializeForSharepoint();
  }
  public void Dispose() { }
}

And then the FeatureReceiver to alter the app’s Web.Config looks something like this (note I borrowed most of this code from another sample SharePoint project:

//
// this is borrowing heavily from http://www.codeplex.com/SPAXO
// 
public class StartupFeatureReceiver : SPFeatureReceiver
{
  public override void FeatureActivated(
        SPFeatureReceiverProperties properties)
  {
    var webApp = properties.Feature.Parent as SPWebApplication;
    AddWebConfigEntry(webApp);
    UpdateApp(webApp);
  }

  public override void FeatureDeactivating(
        SPFeatureReceiverProperties properties)
  {
    var webApp = properties.Feature.Parent as SPWebApplication;
    RemoveWebConfigEntry(webApp);
    UpdateApp(webApp);
  }


  private static void AddWebConfigEntry(SPWebApplication webApp)
  {
    SPWebConfigModification mod = GetModification();
    var existingModifications = 
             new List<SPWebConfigModification>(
                      webApp.WebConfigModifications);
    if (existingModifications.FindIndex(
                    value =>
                        value.Name == mod.Name &&
                        value.Value == mod.Value &&
                        value.Owner == mod.Owner) == -1)
    {
      // If the modifcation does not already exist 
      // add the entry to the config
      webApp.WebConfigModifications.Add(mod);
    }
  }

  private static void RemoveWebConfigEntry(
            SPWebApplication webApp)
  {
    SPWebConfigModification mod = GetModification();
    webApp.WebConfigModifications.Remove(mod);
  }

  private static SPWebConfigModification GetModification()
  {
    string asmName = typeof(StartupModule).AssemblyQualifiedName;
    string typeName = typeof(StartupModule).FullName;

    return new SPWebConfigModification
      {
        Path = "configuration/system.web/httpModules",
        Name = String.Format(CultureInfo.InvariantCulture,
                "add[@name='{0}'][@type='{1}']",
                typeName, asmName),
        Sequence = 0,
        Owner = asmName,
        Type = SPWebConfigModification.
                    SPWebConfigModificationType.EnsureChildNode,
        Value = String.Format(CultureInfo.InvariantCulture,
                  "<add name='{0}' type='{1}' />",
                  typeName, asmName)
      };
  }

  private static void UpdateApp(SPWebApplication webApp)
  {
    // Update the Web App and apply the changes 
    // to all servers in the farm
    webApp.Update();
    webApp.Farm.Services
        .GetValue<SPWebService>()
        .ApplyWebConfigModifications();
  }
}