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• Weighted round robins via TTL - possible?

  - by Joe Hopfgartner

  I currently use DNS round robin for load balancing, which works great. The records look like this (I have a ttl of 120 seconds) ;; ANSWER SECTION: orion.2x.to. 116 IN A 80.237.201.41 orion.2x.to. 116 IN A 87.230.54.12 orion.2x.to. 116 IN A 87.230.100.10 orion.2x.to. 116 IN A 87.230.51.65 I learned that not every ISP / device treats such a response the same way. For example some DNS servers rotate the addresses randomly or always cycle them through. Some just propagate the first entry, others try to determine which is best (regionally near) by looking at the ip address. However if the userbase is big enough (spreads over multiple ISPs etc) it balances pretty well. The discrepancies from highest to lowest loaded server hardly every exceeds 15%. However now I have the problem that I am introducing more servers into the systems, that not all have the same capacities. I currently only have 1gbps servers, but I want to work with 100mbit and also 10gbps servers too. So what I want is I want to introduce a server with 10 GBps with a weight of 100, a 1 gbps server with a weight of 10 and a 100 mbit server with a weight of 1. I used to add servers twice to bring more traffic to them (which worked nice. the bandwidth doubled almost.) But adding a 10gbit server 100 times to DNS is a bit rediculous. So I thought about using the TTL. If I give server A 240 seconds ttl and server B only 120 seconds (which is about about the minimum to use for round robin, as a lot of dns servers set to 120 if a lower ttl is specified.. so i have heard) I think something like this should occour in an ideal scenario: first 120 seconds 50% of requests get server A -> keep it for 240 seconds. 50% of requests get server B -> keep it for 120 seconds second 120 seconds 50% of requests still have server A cached -> keep it for another 120 seconds. 25% of requests get server A -> keep it for 240 seconds 25% of requests get server B -> keep it for 120 seconds third 120 seconds 25% will get server A (from the 50% of Server A that now expired) -> cache 240 sec 25% will get server B (from the 50% of Server A that now expired) -> cache 120 sec 25% will have server A cached for another 120 seconds 12.5% will get server B (from the 25% of server B that now expired) -> cache 120sec 12.5% will get server A (from the 25% of server B that now expired) -> cache 240 sec fourth 120 seconds 25% will have server A cached -> cache for another 120 secs 12.5% will get server A (from the 25% of b that now expired) -> cache 240 secs 12.5% will get server B (from the 25% of b that now expired) -> cache 120 secs 12.5% will get server A (from the 25% of a that now expired) -> cache 240 secs 12.5% will get server B (from the 25% of a that now expired) -> cache 120 secs 6.25% will get server A (from the 12.5% of b that now expired) -> cache 240 secs 6.25% will get server B (from the 12.5% of b that now expired) -> cache 120 secs 12.5% will have server A cached -> cache another 120 secs ... i think i lost something at this point but i think you get the idea.... As you can see this gets pretty complicated to predict and it will for sure not work out like this in practice. But it should definitely have an effect on the distribution! I know that weighted round robin exists and is just controlled by the root server. It just cycles through dns records when responding and returns dns records with a set propability that corresponds to the weighting. My DNS server does not support this, and my requirements are not that precise. If it doesnt weight perfectly its okay, but it should go into the right direction. I think using the TTL field could be a more elegant and easier solution - and it deosnt require a dns server that controls this dynamically, which saves resources - which is in my opinion the whole point of dns load balancing vs hardware load balancers. My question now is... are there any best prectices / methos / rules of thumb to weight round robin distribution using the TTL attribute of DNS records? Edit: The system is a forward proxy server system. The amount of Bandwidth (not requests) exceeds what one single server with ethernet can handle. So I need a balancing solution that distributes the bandwidth to several servers. Are there any alternative methods than using DNS? Of course I can use a load balancer with fibre channel etc, but the costs are rediciulous and it also increases only the width of the bottleneck and does not eliminate it. The only thing i can think of are anycast (is it anycast or multicast?) ip addresses, but I don't have the means to set up such a system.

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• What arguments can I use to "sell" the BDD concept to a team reluctant to adopt it?

  - by S.Robins

  I am a bit of a vocal proponent of the BDD methodology. I've been applying BDD for a couple of years now, and have adopted StoryQ as my framework of choice when developing DotNet applications. Even though I have been unit testing for many years, and had previously shifted to a test-first approach, I've found that I get much more value out of using a BDD framework, because my tests capture the intent of the requirements in relatively clear English within my code, and because my tests can execute multiple assertions without ending the test halfway through - meaning I can see which specific assertions pass/fail at a glance without debugging to prove it. This has really been the tip of the iceberg for me, as I've also noticed that I am able to debug both test and implementation code in a more targeted manner, with the result that my productivity has grown significantly, and that I can more easily determine where a failure occurs if a problem happens to make it all the way to the integration build due to the output that makes its way into the build logs. Further, the StoryQ api has a lovely fluent syntax that is easy to learn and which can be applied in an extraordinary number of ways, requiring no external dependencies in order to use it. So with all of these benefits, you would think it an easy to introduce the concept to the rest of the team. Unfortunately, the other team members are reluctant to even look at StoryQ to evaluate it properly (let alone entertain the idea of applying BDD), and have convinced each other to try and remove a number of StoryQ elements from our own core testing framework, even though they originally supported the use of StoryQ, and that it doesn't impact on any other part of our testing system. Doing so would end up increasing my workload significantly overall and really goes against the grain, as I am convinced through practical experience that it is a better way to work in a test-first manner in our particular working environment, and can only lead to greater improvements in the quality of our software, given I've found it easier to stick with test first using BDD. So the question really comes down to the following: What arguments can I use to really drive the point home that it would be better to use StoryQ, or at the very least apply the BDD methodology? Can you point me to any anecdotal evidence that I can use to support my argument to adopt BDD as our standard method of choice? What counter arguments can you think of that could suggest that my wish to convert the team efforts to BDD might be in error? Yes, I'm happy to be proven wrong provided the argument is a sound one. NOTE: I am not advocating that we rewrite our tests in their entirety, but rather to simply start working in a different manner for all future testing work.

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• Exchange ActiveSync with multiple email addresses

  - by Martin Robins

  I have Exchange 2007 SP2, and I have successfully connected my Windows Mobile phone via Exchange ActiveSync and can send and receive emails. I have two addresses within my Exchange mailbox, [email protected] and [email protected], with the second being set as the reply address. When I view my email addresses on my device, I see both of these email addresses, however when I send new messages it always selects the first email address as the reply address and not the second. It is probably worth pointing out that, like in the example provided above, the email addresses are shown alphabetically and the address being selected is the first alphabetically (just in case that matters). I would like to set the device to always select the reply address specified in the mailbox, or at least be able to ensure that the address I want is selected if I have to select it manually on the device, but cannot find any way to make this happen. Can anybody help?

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• Exchange ActiveSync with muliple email addresses

  - by Martin Robins

  I have Exchange 2007 SP2, and I have successfully connected my Windows Mobile phone via Exchange ActiveSync and can send and receive emails. I have two addresses within my Exchange mailbox, [email protected] and [email protected], with the second being set as the reply address. When I view my email addresses on my device, I see both of these email addresses, however when I send new messages it always selects the first email address as the reply address and not the second. It is probably worth pointing out that, like in the example provided above, the email addresses are shown alphabetically and the address being selected is the first alphabetically (just in case that matters). I would like to set the device to always select the reply address specified in the mailbox, or at least be able to ensure that the address I want is selected if I have to select it manually on the device, but cannot find any way to make this happen. Can anybody help?

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• Data Recovery needed with a Sector Zero problem on a HDD

  - by Jay Robins

  Left my computer (running XP) copying files to an external drive. Came back a few hours later, and the laptop was pretty hot and had frozen (Ironic aint it). Forced a reboot, and the laptop HDD hasnt worked since. Set it up in an external enclosure, but XP cant mount the HDD to a drive letter, but is able to recognize the manufacturer and drive size (Hitachi-320GB). No noise or rattling when the drive is spinning, but I cant get anything off of it, since i cant mount it, or see much of anything. Computer repair shop ran some software tests and says it came back with a "Zero Sector bad" message, and need to send it to a professional data recovery service. Any other options or ideas, before I have to spend thousands of dollars to recover my data? Any help would be GREATLY appreciated!!! I'm desperate and a poor student! Thanks in Advance, -Jay

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• How can I make this work with deep properties

  - by Martin Robins

  Given the following code... class Program { static void Main(string[] args) { Foo foo = new Foo { Bar = new Bar { Name = "Martin" }, Name = "Martin" }; DoLambdaStuff(foo, f => f.Name); DoLambdaStuff(foo, f => f.Bar.Name); } static void DoLambdaStuff<TObject, TValue>(TObject obj, Expression<Func<TObject, TValue>> expression) { // Set up and test "getter"... Func<TObject, TValue> getValue = expression.Compile(); TValue stuff = getValue(obj); // Set up and test "setter"... ParameterExpression objectParameterExpression = Expression.Parameter(typeof(TObject)), valueParameterExpression = Expression.Parameter(typeof(TValue)); Expression<Action<TObject, TValue>> setValueExpression = Expression.Lambda<Action<TObject, TValue>>( Expression.Block( Expression.Assign(Expression.Property(objectParameterExpression, ((MemberExpression)expression.Body).Member.Name), valueParameterExpression) ), objectParameterExpression, valueParameterExpression ); Action<TObject, TValue> setValue = setValueExpression.Compile(); setValue(obj, stuff); } } class Foo { public Bar Bar { get; set; } public string Name { get; set; } } class Bar { public string Name { get; set; } } The call to DoLambdaStuff(foo, f => f.Name) works ok because I am accessing a shallow property, however the call to DoLambdaStuff(foo, f => f.Bar.Name) fails - although the creation of the getValue function works fine, the creation of the setValueExpression fails because I am attempting to access a deep property of the object. Can anybody please help me to modify this so that I can create the setValueExpression for deep properties as well as shallow? Thanks.

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• asp.net 4.0 web forms routing - default/wildcard route

  - by Martin Robins

  I there a simple way when using ASP.NET 4.0 routing with Web Forms to produce a route that will act as some kind of wildcard? It seems to me that within WebForms, you have to specify a route for every page - I am looking for some kind of generic route that can be used where nothing specific is required, perhaps mapping directly from path to path so... http://somedomain.com/folder1/folder2/page would possibly map to folder1/folder2/page.aspx Any suggestions? Thanks

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• Windows Mobile: "My network card connects to" registry settings

  - by Martin Robins

  Can anybody please tell me the registry setting(s) that are affected in Windows Mobile 6.1 when a user selects Start - Settings - Connections - Wi-Fi and then changes the value of the "My network card connects to" drop down list on the "Network Adapters" tab? I have a device that seems to default this to "The Internet" when in fact the Wi-Fi connects to the corporate network and I would like to be able to change this programatically rather than expecting 250+ users to have to do it manually every time they reboot their devices. Thanks.

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• Create lambda action from function expression

  - by Martin Robins

  It is relatively easy to create a lambda function that will return the value of a property from an object, even including deep properties... Func<Category, string> getCategoryName = new Func<Category, string>(c => c.Name); and this can be called as follows... string categoryName = getCategoryName(this.category); But, given only the resulting function above (or the expression originally used to create the function), can anybody provide an easy way to create the opposing action... Action<Category, string> setCategoryName = new Action<Category, string>((c, s) => c.Name = s); ...that will enable the same property value to be set as follows? setCategoryName(this.category, ""); Note that I am looking for a way to create the action programatically from the function or expression - I hope that I have shown that I already know how to create it manually. I am open to answers that work in both .net 3.5 and 4.0. Thanks.

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• How can I get my meshes to work with Bullet Physics?

  - by Molmasepic

  The problem is that I'm trying to use my meshes with Bullet Physics for the collision part of my game. When I attempted doing this method with my GLM(model loading library by nate robins) model, I get a segmentation fault in the debug, so I figured that it doesnt like the coordinate variables of the model. If i use blender to export my model as a collision file, what type of file should I use? I have heard of a .bullet exporter, but i dont know hot to integrate this python script into my Blender 2.5 program.

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• Is there a simple Load Balancer app for development environment on Windows?

  - by djangofan

  Does there exist a simple Load Balancer app for development on Windows? I am running a pair of JBoss 5.x instances in a cluster on a single machine. Normally , this configuration is load balanced by a nice hardware load balancer but I am wondering if there is a simple piece of software to enable load balancing in my Eclipse dev environment. Basically, for example, I want a load balancer running on port 11111 that round-robins between the 2 clustered JBoss instances on ssl ports 8443 and 8543 . (or http port if thats not possible) I know that Glassfish has a built-in load balancer but I can't use Glassfish. One idea I have is to try to setup a separate instance of Tomcat with the "balancer" web app. Im trying that now... not sure if it will work... and its a complicated setup and I wish there was something really easy.

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• MS Tech Ed 2011 Coming Soon

  - by sonam

  Microsoft Tech ed 2010 was a great success. Infact  Most of such conferences always provide a great place to meet other  technology enthusiasts and ofcourse,whats in the pipeline for future products of a company or field.. And yet again,MS Tech ed India is coming on 23-25 march  in Banglore,India.Well,the place is  ofcourse right suited for any IT/Computing conference.After all,Its Silicon Valley of India.. From Last year.I remember  a session by Harish about  “Building pure client side apps with  Jquery and Microsoft Ajax .” Here’s the video: http://live.viasilverlight.com/TechEdOnDemand/Breakouts/TheWebSimplified1/Session4/AjaxClientSideApps.wmv At that time only,I got to know that jquery is so easy to use for  ajax or client side templating.Though I prefer jquery over  Microsoft Ajax many folds.UpdatePanel  is Dead for sure in my view. I believe,Web forms will be dead sooner or later with ASP.Net  MVC  gaining share many folds.(TODO:Learn MVC). The new standard is surely:JQUERY . Between,Last years videos and ppt’s  are available to browse and download: http://microsoftteched.in/2010/downloads.aspx After going through Tech Ad 2011 session agendas : http://www.microsoft.com/india/teched2011/agenda.aspx Few of my personal choices to watch would be: Day 1: a) Identity And Access Control in the Cloud        b)Windows 7 at  Home:Digitizing your Home.(Sounds cool.)        c) And ofcourse,Jquery and MS ajax(Lets see if MS can do something that’s not already happening with their version Of Ajax).. Day 2:  a) Lap Around Silverlight 5 and Html 5 as I have heard some hot talks that html5 will kill Silverlight,(I don’t see it in near future though).        b) Html 5 more than “Html 5”…Google will be seeing this one. Day3: a) Cross Browser applications in Azure       b)VS 2010 sessions of automated testing azure apps etc. Windows Phone 7 sessions will surely be of more interest now after MS-Nokia Deal. Though,Personally,I would want atleast some worth of  sessions on MS  future in Robotics,AI.Perhaps  I am looking at wrong place..(When is PDC?) And Since,Bill Gates  consider Robotics as the next big thing, Refer  this one : http://www.cs.virginia.edu/robins/A_Robot_in_Every_Home.pdf  I am sure,they wont loose this new hot spot to competitors,  like how google rules in Online  Search now.Robotics and AI will surely provide a big battlefield  for future.See,What IBM is doing with IBM Watson. OR see this, http://www.sciencedaily.com/releases/2011/02/110218083711.htm this is cool only if you can control your mind.Atleast,I’ll prefer regular driving (I would devote my mind seeing  people,places which we see on road).thats what jouney makes “cool”.:P.

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• Push-Based Events in a Services Oriented Architecture

  - by Colin Morelli

  I have come to a point, in building a services oriented architecture (on top of Thrift), that I need to expose events and allow listeners. My initial thought was, "create an EventService" to handle publishing and subscribing to events. That EventService can use whatever implementation it desires to actually distribute the events. My client automatically round-robins service requests to available service hosts which are determined using Zookeeper-based service discovery. So, I'd probably use JMS inside of EventService mainly for the purpose of persisting messages (in the event that a service host for EventService goes down before it can distribute the message to all of the available listeners). When I started considering this, I began looking into the differences between Queues and Topics. Topics unfortunately won't work for me, because (at least for now), all listeners must receive the message (even if they were down at the time the event was pushed, or hadn't made a subscription yet because they haven't completed startup (during deployment, for example) - messages should be queued until the service is available). However, I don't want EventService to be responsible for handling all of the events. I don't think it should have the code to react to events inside of it. Each of the services should do what it needs with a given event. This would indicate that each service would need a JMS connection, which questions the value of having EventService at all (as the services could individually publish and subscribe to JMS directly). However, it also couples all of the services to JMS (when I'd rather that there be a single service that's responsible for determining how to distribute events). What I had thought was to publish an event to EventService, which pulls a configuration of listeners from some configuration source (database, flat file, irrelevant for now). It replicates the message and pushes each one back into a queue with information specific to that listener (so, if there are 3 listeners, 1 event would become 3 events in JMS). Then, another thread in EventService (which is replicated, running on multiple hots) would be pulling from the queue, attempting to make the service call to the "listener", and returning the message to the queue (if the service is down), or discarding the message (if the listener completed successfully). tl;dr If I have an EventService that is responsible for receiving events and delegating service calls to "event listeners," (which are really just endpoints on other services), how should it know how to craft the service call? Should I create a generic "Event" object that is shared among all services? Then, the EventService can just construct this object and pass it to the service call. Or is there a better answer to this problem entirely?

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• Why does one loop take longer to detect a shared memory update than another loop?

  - by Joseph Garvin

  I've written a 'server' program that writes to shared memory, and a client program that reads from the memory. The server has different 'channels' that it can be writing to, which are just different linked lists that it's appending items too. The client is interested in some of the linked lists, and wants to read every node that's added to those lists as it comes in, with the minimum latency possible. I have 2 approaches for the client: For each linked list, the client keeps a 'bookmark' pointer to keep its place within the linked list. It round robins the linked lists, iterating through all of them over and over (it loops forever), moving each bookmark one node forward each time if it can. Whether it can is determined by the value of a 'next' member of the node. If it's non-null, then jumping to the next node is safe (the server switches it from null to non-null atomically). This approach works OK, but if there are a lot of lists to iterate over, and only a few of them are receiving updates, the latency gets bad. The server gives each list a unique ID. Each time the server appends an item to a list, it also appends the ID number of the list to a master 'update list'. The client only keeps one bookmark, a bookmark into the update list. It endlessly checks if the bookmark's next pointer is non-null ( while(node->next_ == NULL) {} ), if so moves ahead, reads the ID given, and then processes the new node on the linked list that has that ID. This, in theory, should handle large numbers of lists much better, because the client doesn't have to iterate over all of them each time. When I benchmarked the latency of both approaches (using gettimeofday), to my surprise #2 was terrible. The first approach, for a small number of linked lists, would often be under 20us of latency. The second approach would have small spats of low latencies but often be between 4,000-7,000us! Through inserting gettimeofday's here and there, I've determined that all of the added latency in approach #2 is spent in the loop repeatedly checking if the next pointer is non-null. This is puzzling to me; it's as if the change in one process is taking longer to 'publish' to the second process with the second approach. I assume there's some sort of cache interaction going on I don't understand. What's going on?

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