I’ve known about vaasnet for quite a while.  Basically, vaasnet is a way to almost instantly (OK, it took about 4 seconds to come up) grab a fresh VM (currently 99 cents an hour), do a bunch of stuff and go away.  My bunch of stuff was I need to download a bittorrent file that was about 5 gig and I know if I do it from either home or over my hotspot, bad things will happen.  If I do it at home, Comcast will send me a letter accusing me of stealing something, and if I use my Verizon hotspot, well, it’s a 5 gig per month plan.  You do the math.

Back to vaasnet.  Here is my experience today:

1. 30 seconds to put my credit card it
2. 4 seconds to boot a general purpose workstation
3. 5 seconds to RDP into it
4. 2 minutes to download bit torrent
5. 35 minutes to have bit torrent download a 5 gig file!
6. 35 minutes to have bit torrent download a 5 gig file (had to say it twice)
7. 1 minute to transfer the file to my ORCSWeb server I already have
8. $1.70 billed to my credit card.
9. OMG!

I think that about says it all.  OK, maybe not it all.

I’ll be back!

OK, now that says it all.

If you’ve started using SqlAzure for your SqlServer with your Azure application, you’ve probably discovered that you get a reasonable number of connection failures.  The advice from the Azure team is add retry logic to all your connections to SqlAzure. There is a long discussion posted by the Azure team here.

The key paragraph states the problem as follows:

The Problem
One of the things that SQL Azure does to deliver high availability is it sometimes closes connections. SQL Azure does some pretty cool stuff under the covers to minimize the impact, but this is a key difference in SQL Azure development vs. SQL Server development.

Basically, what this means is that you must be able to deal with connections failing when you call SqlAzure.  Something that all of probably should have been doing forever, but because most of the time SqlServer is running on your local LAN and the likelihood if a connection failing was next to zero unless something else was going terribly wrong.  Certainly not something we had to do on regular basis.  To emphasize that even more, most of the controls built into asp.net that open connections to sqlserver don’t even do this and that’s from Microsoft itself.

The solution proposed in the thread mentioned above basically has you add tons of code to everyplace you access a connection object.  Personally, I don’t like that because I have hundreds if not thousands of places I open connections and inserting tens of thousands of lines of extra new untested code is a little scary.

So, what to do?

Fortunately, another team at Microsoft, known as the Windows Server AppFabric Customer Advisory Team published a general purpose solution using Extension Methods and some darn clever coding wrote a great article and published code including azure examples that solves this problem very elegantly without requiring a lot of changes to your existing code base.

In this article I plan on giving an example and publishing a sample project that uses this code with SqlAzure to solve the connection retry problem.  My goal here is not to simply restate what they published but to simply have a very simple concrete example of using their library.

Design Goal

We have two goals.

1. Change as little code as possible
2. Log Connection Errors when they happen With Locations
3. Make sure not to trap errors that are NOT connection related such as bad column names

Incorrect Code

So, this is what the original code looks like that will fail because it does not have connection retry logic:

public static int UsersIdFromUserNameNoConnectionRetry(string userName){    var retUsersId = 0;    const string sql =        @"SELECT Id FROM Users            WHERE Username = @Username";

    using (var sqlConnection = new SqlConnection(            ConfigurationManager.ConnectionStrings["CRStorageWebConnectionString"].            ConnectionString))    {        sqlConnection.Open();        using (var sqlCommand = new SqlCommand(sql, sqlConnection))        {            sqlCommand.Parameters.Add("@Username", SqlDbType.NVarChar).Value = userName;            using (var reader = sqlCommand.ExecuteReader())            {                while (reader.Read())                {                    retUsersId = reader.IsDBNull(0) ? 0 : reader.GetInt32(0);                }            }        }    }    return retUsersId;}

So, if there is a connection, an exception will get thrown and will need to be caught, but then the method will not have done it’s job.

Correct Code With Retries

So, now take a look at the revised code after the library is setup and used.  The setup is non-trivial, but you just have to do that once and then you can simply fix all your other code with very few changes.  Below is the new code with connection retry logic built in.

public static int UsersIdFromUserName(string userName){    var retUsersId = 0;    const string sql =        @"SELECT Id FROM Users            WHERE Username = @Username";

    using (var sqlConnection =        new ReliableSqlConnection(            ConfigurationManager.ConnectionStrings["CRStorageWebConnectionString"].            ConnectionString,            new RetryUtils("", "UsersIdFromUserName").GetRetryPolicy()))    {        sqlConnection.Open();        using (var sqlCommand = new SqlCommand(sql, sqlConnection.Current))        {            sqlCommand.Parameters.Add("@Username", SqlDbType.NVarChar).Value = userName;            using (var reader = sqlCommand.ExecuteReader())            {                while (reader.Read())                {                    retUsersId = reader.IsDBNull(0) ? 0 : reader.GetInt32(0);                }            }        }    }    return retUsersId;}

1. The first is instead of create an SqlConnection(…) we are creating a ReliableSqlConnection(…).  The ReliableSqlConnection takes an extra parameter which basically wraps the retry logic used, as well as labelling this connection so when it fails, it gets logged.  In the log, there will be the comment “UsersIdFromUserName” so we know what method threw the retry.
2. The second is slight change we when we create the SqlCommand, we have to add the property .Current to it so we know we are talking about the currently executing connection.  There may be a default way to handle this but I could not figure it out.

The Setup Pieces

The project has all kinds of stuff in it that build quite nicely, run and test under vs2010.  All I’m interested in is the ado.net piece and the retry logic around that.  I actually used the 1.2 version, however I now see there is a 1.3 version with some improvements.  I would post my project but I don’t want to post it with old code so I’ll just tell you the steps I went through so you can do the same.

Build the class library

Compile the project and make sure you have the dll from the library lincluded in your actual visual studio project.  The library you want is Microsoft.AppFabricCAT.Samples.Azure.TransientFaultHandling.

Update Your Web.config

Add the config section below to your web.config file.

<configSections>    <section name="RetryPolicyConfiguration"          type="Microsoft.AppFabricCAT.Samples.Azure.TransientFaultHandling.Configuration.RetryPolicyConfigurationSettings,            Microsoft.AppFabricCAT.Samples.Azure.TransientFaultHandling" /></configSections>

<RetryPolicyConfiguration defaultPolicy="FixedIntervalDefault" defaultSqlConnectionPolicy="FixedIntervalDefault"          defaultSqlCommandPolicy="FixedIntervalDefault" defaultStoragePolicy="IncrementalIntervalDefault"          defaultCommunicationPolicy="IncrementalIntervalDefault">    <add name="FixedIntervalDefault" maxRetryCount="10" retryInterval="100" />    <add name="IncrementalIntervalDefault" maxRetryCount="10" retryInterval="100" retryIncrement="50" />    <add name="ExponentialIntervalDefault" maxRetryCount="10" minBackoff="100" maxBackoff="1000" deltaBackoff="100" /></RetryPolicyConfiguration>

This defines a new section in your web.config, then implements it with several different retry policies include a default one which seems quite reasonable to me.

If you remember, in the implementation section above, we used a public class called RetryUtils.  This class is actually one I invented as a convenience class to minimize the code I have to update on each use of the ReliableConnection Object.  Just to refresh your memory, the implementation is this:

using (var sqlConnection =                new ReliableSqlConnection(                    ConfigurationManager.ConnectionStrings["CRStorageWebConnectionString"].                    ConnectionString,                    new RetryUtils("", "UsersIdFromUserName").GetRetryPolicy()))

The actual code fo rthe class RetryUtils is below here.  You’ll have to stick this someplace in your project.

namespace Utils{

    public class RetryUtils    {        public string Username { get; set; }        public string CallersName { get; set; }

        public RetryUtils(string username, string callersName)        {            Username = username;            CallersName = callersName;        }

        public RetryUtils()        {            Username = string.Empty;            CallersName = string.Empty;        }

        public RetryPolicy<SqlAzureTransientErrorDetectionStrategy> GetRetryPolicy()        {            var retryPolicy = new RetryPolicy<SqlAzureTransientErrorDetectionStrategy>                 (RetryPolicy.DefaultClientRetryCount, RetryPolicy.DefaultMinBackoff,                  RetryPolicy.DefaultMaxBackoff,                  RetryPolicy.DefaultClientBackoff);

            retryPolicy.RetryOccurred += RetryPolicyRetryOccurred;

            return retryPolicy;        }

        void RetryPolicyRetryOccurred(int currentRetryCount, Exception lastException, TimeSpan delay)        {            GeneralUtils.GetLog4NetAllDataContext().AddLog4NetAll(new Log4NetAll                                                    {                                                        Date = DateTime.UtcNow,                                                        EllapsedTime = 0,                                                        ExceptionStackTrace = lastException.StackTrace,                                                        Message = "RetryCount: " + currentRetryCount + " delay: " + delay.Seconds,                                                        ExceptionMessage = lastException.Message,                                                        Logger = "",                                                        Level = "Error",                                                        UserName = Username,                                                        PartitionKey = Username,                                                        RowKey = Guid.NewGuid().ToString()                                                    });        }           }}

Non Connection Related Errors

Conclusions

The actual presentation was done at the Microsoft office in San Francisco.

	Title Of Each Article	Video Included With Each Post
Part 1	Introduction To RIA Services In Silverlight (This Article)	7 Minutes
Part 2	Basic RIA Services And DataGrid With  VS 2010 Tooling	14 Minutes
Part 3	Adding A DataGrid With Connect The Dots DataBinding in VS 2010	13 Minutes
Part 4	Adding a Navigation Page to a Silverlight Business Application Template	11 Minutes
Part 5	Adding Speakers Page Template With Converters In Visual Studio 2010 Beta2	11 Minutes
Part 6	Adding A Sessions Page That Includes a Query Parameter In Silverlight VS2010 Beta2	10 Minutes
Part 7	Basic Authentication and Authorization In RIA Services	5 Minutes

I’ve heavily borrowed from Brad Abrams PDC09 presentation here and am very thankful for the help.  I’m personally very excited about the opportunities RIA Services gives us as developers to efficiently build powerful multi tier applications without compromise.

I’d recommend going to Brad Abrams PDC09 presentation mentioned above to get a better understanding of what Microsoft was thinking and its plans for RIA Services. The way I see it is RIA Services is built on the WCF Stack.  It basically is a technology that let’s the developer create both client and server code at the same time.  It essentially removes the middle layer form a development perspective, but keeps it there in a very physical way using all the power of WCF.  For example, you create you logic on the server side and that code automatically gets migrated to the client for simplicity of calling.

For those interested where the motivation came from to to this, it’s an interesting story.  Last week, Mathias Brandewinder, the organizer of our local Bay.Net San Francisco user group emailed and asked if I could fill in last minute for the upcoming (actually today’s) bay.net meeting and, could I talk about RIA Services.  Well, 2 years or so ago, I did a quite extensive Silverlight 1.1 project for Leverage Software using the first beta of the .CLR release of Silverlight (C#).  I have to say, it was an awful experience.  So, now at Silverlight 4.0, RIA Services, I’m back and very excited.

By way of people that have helped me in the last week to get this far, just to name a few:  Bruno Terkaly, offering to do whatever he could and giving me tech tips, Michael Scherotter in “going to town” as he says to make the Speaker’s page look really nice in a live meeting, Victor Gaudioso in taking time on his busy weekend to call me  and offer help, Brad Abrams putting up with my list of naive questions and patiently responding, a slew of ASPInsiders who pointed me at an excellent place to host the videos, and David Kelly for giving me a nicely styled Silverlight player to show the videos on this blog.

I’m sitting in the mall below the Microsoft Office in San Francisco where the presentation will be in about 2 hours.  Hopefully, I’ll finish all seven articles and get them posted to the internet very soon.  I did the videos as just practice for my presentation.  They are not polished or edited.  I’m taking the chance of posting them in the hopes that they help someone struggling with all the new features like I have been during the last week.

Finally, this demo is built on live Silicon Valley Code Camp Data that has been collected over the past 4 years.  I can’t really publish that database along with the completed solution before I clean and randomize the attendee data.  Meanwhile, I will post the project code but it will not work until I’ve had a chance to clean up the database.  My thinking is that it’s all positive and better to release the code now rather than wait until I have the database cleaned up.

Below is what the end result of what we are building will look like (if you make it through all the articles and videos).

Attached here is source that you can build with Visual Studio 2010 Beta 2 and it will work with No Database.  The Domain Class is heavily modified from what is presented, but it will allow you to actually run and play with real data.

The company I’m now working at is small and we don’t have a lot of resources to maintain hardware and do operating system type support.  We do have a high load requirement so we need a very robust supported solution.  Before this, I’d always been in the under $50 per month type plan with ORCSWeb, but I decided I needed more servers and a higher level of support.  I really did not know what level of support to expect when signing up for the managed servers but decided to go for it anyway.

All  can say is WOW!!!  I am over the top impressed.

We currently have 3 virtual servers hosted at ORCSWeb.  One, we use as a development server, and the other two are in a webfarm configuration.  I’ve always believed that when you go into production with a web site it’s critical you start with 2 servers in a webfarm.  it’s really easy to go from 2 to 10, but can be very painful to go from 1 to 2.   That’s a topic for another post, but suffice it to say, 2 is the minimum.

So, why am I so impressed?  First, the support team they assigned to me is totally awesome.  They all are focussed and competent which is a total relief compared with most hosting companies I’ve dealt with.  Other companies always have good people, but it seems to be the bad ones that really give me cause to remember.  Second, because I paid extra for the full managed support options on our three servers, I’ve been able to ask the things like the following.  Almost all of them I could do myself, but I’m swamped with my technology role in the new company and really appreciate being able to hand stuff like this off.

• I’ve pointed my MX record at my .149 server.  Could you please set up email and create the following 7 accounts.
• Please Setup a secure ftp server at the following address with the following username and password (and make sure the user is locked down to the root)
• Setup DFS Replication between these two directories on .148 and .149
• Create a RoboCopy script that copies files from my dev server to the .149 mirrored directory
• Please set up web statistics for me on http://www.siliconvalley-codecamp.com
• Please figure out why SqlServer 2008 is not letting me access catalog MyStuff1 from user 3p1 and fix
• Please make a replicate of website MyWeb1.com including the sqlserver catalog’s and put it on MyWeb2.com on server .149
• Please replace the sqlserver catalog MyStuff3 on server .149 with the bak file I uploaded to my ftp server
• I could go on and on, but I think you are getting the idea.
• Always with a smile, 24×7, what else can I say.

By the way, if you want to see one of my sites hosted there, go to http://www.siliconvalley-codecamp.com

Thank you ORCSWeb for making things a lot easier for me.

 function pageLoad() {

        req = new ActiveXObject("Msxml2.XMLHTTP");

        if (req) {

            req.onreadystatechange = processStateChange;

            req.open("GET", "AttendeeZipCode.ashx", true);

            req.send();

        }

    }

    function processStateChange() {

        statusDiv = document.getElementById("stats");

        if (req.readyState == 0) { statusDiv.innerHTML = "UNINITIALIZED"; }

        if (req.readyState == 1) { statusDiv.innerHTML = "LOADING"; }

        if (req.readyState == 2) { statusDiv.innerHTML = "LOADED"; }

        if (req.readyState == 3) { statusDiv.innerHTML = "INTERACTIVE"; }

        if (req.readyState == 4) {

            //statusDiv.innerHTML = "COMPLETE";

            GetMap();

            //statusDiv.innerHTML = req.responseText;

            var dataObject = json_parse(req.responseText);

            CreateLayerAttendees();

            CreateLayerSpeakers();

            var points = new Array();

            for (var i = 0; i < dataObject.length; i++) {

                var lattitude = dataObject[i].lattitude;

                var longitude = dataObject[i].longitude;

                points[i] = new VELatLong(lattitude, longitude);

                if (dataObject[i].isSpeaker) {

                    AddOnePin(layerSpeaker, lattitude, longitude, "x", "x", true);

                }

                else {

                    AddOnePin(layerAttendee, lattitude, longitude, "x", "x", false);

                }

                AddOnePin(layerAttendee, lattitude, longitude, "x", "x",dataObject[i].isSpeaker);

            }

            map.SetMapView(points);

        }

    }

Well, that worked great until I ran it on Firefox and Chrome.  Basically, nothing happened.  So, off to my smart friends at the local Java Users Group and they suggested I should use a JavaScript library because my solution only works for IE.  With that hint, I grabbed my favorite AJAX book by Alessandro Gallo, Ajax in Action and started reading.  Turns out, there is indeed a Microsoft Ajax Library solution to this and here it is.

 function pageLoad() {

            var request = new Sys.Net.WebRequest();

            request.set_url("AttendeeZipCode.ashx");

            request.add_completed(onRequestCompleted);

            request.invoke();

        }

        function onRequestCompleted(executor, args) {

            processResults(executor.get_responseData());

        }

Now, Firefox, Chrome, and IE all work!  and, look what a nice result we get.

Hope this helps!

So, as is normal, when I learn something new, the most obvious things just don’t seem to work.  In this case, I’m just trying to make a web page that shows a list of data on a page.  I’m not going to try and teach MVC here, but if you are like me and struggled with this, this should help you get through some of the tough spots. My plan is to start a new MVC project with Visual Studio and show you what is necessary to generate the list.  Instead of going after a database, I’m going to use an simple business object class so you can run this without connecting to a database.  Not sure about you, but I never seem to be able to get the databases from example code working.  Scott Guthrie uses the Northwind databases Product table, and after spending about 15 minutes searching, all I could find was a Northwind database from sqlserver 2000 that does not have a Product table.  With my demo, you won’t have to worry about that.  By the way, here is the project if you want to download it in action.

So, Here we go.  First thing, Open Visual Studio 2008 and create a new MVC Project (not a web site, this will give you a csproj type file)

Answer the next question YES because of course you want a Test Project.

You should get a Solution that looks like this:

Now, Add the business object that I will be using for this rest of this demonstration.  It’s in the project file, our you just download it here (put this in your Models Directory).

Now, let’s create the MVC Controller.  Highlight the Controller’s Folder and say Add Item (TMI if I show you that).  Here is the dialog.  Create the name of your controller with the syntax {Name}Controller.  In my case, the name is EmailListControler.cs.

Add the following code to your EmailListController.cs file to retrieve some data and return it as a View (which will be processed by the View Page coming up).

using System.Collections.Generic;

using System.Linq;

using System.Web.Mvc;

namespace Solution.Controllers

{

    public class EmailListController : Controller

    {

        public ActionResult Index()

        {

            var businessObject = new BusinessObject();

            List<BusinessObjectItem> members = 

                businessObject.GetMembers();

            return View("Index", members);

        }

    }

}using System.Collections.Generic;

using System.Linq;

using System.Web.Mvc;

namespace Solution.Controllers

{

    public class EmailListController : Controller

    {

        public ActionResult Index()

        {

            var businessObject = new BusinessObject();

            List<BusinessObjectItem> members = 

                businessObject.GetMembers();

            return View("Index", members);

        }

    }

}

Then, create a new folder called EmailList under the Views folder.

Then, create a MVCViewPage in the EmailList folder called Index.aspx.

(Actually, choose MVC View Content Page, not MVC View Page)

Then, chose the Master Page to use as follows (there is only one):

The View will be referring to the ViewData.Model which somehow is associated with how the code behind is implemented. Make sure you have the ViewPage look like the following and the data type specified as below.  This is the file Index.aspx.cs which is in your email directory.

using System.Collections.Generic;

using System.Web.Mvc;

namespace Solution.Views.EmailList

{

    public partial class Index :

        ViewPage<IEnumerable<BusinessObjectItem>>

    {

    }

}

Now, for the Index.aspx file which is also in your Views/EmailList directory, enter the following between the content tags.

<table border="1">

    <tr>

        <td>

            <strong>Name</strong>

        </td>

        <td>

            <strong><strong>Email Address</strong>

        </td>

    </tr>

    <% foreach (var emailItem in ViewData.Model)

       { %>

    <tr>

        <td>

            <%= emailItem.Name %>

        </td>

        <td>

            <%=emailItem.Email %>

        </td>

    </tr>

    <% } %>

</table>

Notice that you have intellisense working on your foreach items.

Finally, go to your Master Page and add a link for this new EmailList as follows.  That is, change the file /Views/Shared/Site.Master

<ul id="menu">              

    <li><%= Html.ActionLink("Home", "Index", "Home")%></li>

    <li><%= Html.ActionLink("About Us", "About", "Home")%></li>

    <li><a href="/EmailList">Email List</a></li>

</ul>

As you can see, I don’t quite grock the ActionLinke parameters so I just put in a standard anchor tag.  Please comment below on what it should be to be able to reference /EmailList and I will update the article.  For now, lunch is coming and I need to run.

When you finally run that app, you get this for your new output.  Notice the New Email List Tab.

That’s it for now.  Hope this helps!

The solution involves first dropping a GridView and ObjectDataSource onto your design surface in Visual Studio.  Then, using the little chevron on the GridView, choose edit columns and convert the column you are interested in making a DropDownList into a template.  From there replace the ItemTemplate with the DropDownList code below.  You get the code below.

<%@ Page Language="C#" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<script runat="server">

</script>

<html xmlns="http://www.w3.org/1999/xhtml">

<head runat="server">

    <title>ODS DDL Example</title>

</head>

<body>

    <form id="form1" runat="server">

    <div>

        <asp:ObjectDataSource ID="ObjectDataSource1" runat="server" SelectMethod="GetMembers"

            TypeName="BusinessObject"></asp:ObjectDataSource>

        <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" DataKeyNames="Id"

            DataSourceID="ObjectDataSource1">

            <Columns>

                <asp:BoundField DataField="Id" HeaderText="Id" ReadOnly="True" SortExpression="Id" />

                <asp:BoundField DataField="Name" HeaderText="Name" SortExpression="Name" />

                <asp:BoundField DataField="Email" HeaderText="Email" SortExpression="Email" />

                <asp:TemplateField HeaderText="Approved" SortExpression="Approved">

                    <ItemTemplate>

                        <asp:DropDownList ID="DropDownListUser" runat="server" AutoPostBack="False" 

                            SelectedValue='<%# Bind("Approved") %>'>

                            <asp:ListItem Text="Yes" Value="True"></asp:ListItem>

                            <asp:ListItem Text="No" Value="False"></asp:ListItem>

                        </asp:DropDownList>

                    </ItemTemplate>

                </asp:TemplateField>

            </Columns>

        </asp:GridView>

    </div>

    </form>

</body>

</html>

And, when you run this code (assuming you have a simple business object that returns some data), you get this:

Hope this helps!

And the Power Point Presentation:

Any Questions, feel free to contact me at http://peterkellner.net/contact/