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Scalability 101: How can I design a scalable web application using PHP?

- by Legend

I am building a web-application and have a couple of quick questions. From what I learnt, one should not worry about scalability when initially building the app and should only start worrying when the traffic increases. However, this being my first web-application, I am not quite sure if I should take an approach where I design things in an ad-hoc manner and later "fix" them. I have been reading stories about how people start off with an app that gets millions of users in a week or two. Not that I will face the same situation but I can't help but wonder, how do these people do it? Currently, I bought a shared hosting account on Lunarpages and that got me started in building and testing the application. However, I am interested in learning how to build the same application in a scalable-manner using the cloud, for instance, Amazon's EC2. From my understanding, I can see a couple of components: There is a load balancer that first receives requests and then decides where to route each request This request is then handled by a server replica that then processes the request and updates (if required) the database and sends back the response to the client If a similar request comes in, then a caching mechanism like memcached kicks into picture and returns objects from the cache A blackbox that handles database replication Specifically, I am trying to do the following: Setting up a load balancer (my homework revealed that HAProxy is one such load balancer) Setting up replication so that databases can be synchronized Using memcached Configuring Apache to work with multiple web servers Partitioning application to use Amazon EC2 and Amazon S3 (my application is something that will need great deal of storage) Finally, how can I avoid burning myself when using Amazon services? Because this is just a learning phase, I can probably do with 2-3 servers with a simple load balancer and replication but until I want to avoid paying loads of money accidentally. I am able to find resources on individual topics but am unable to find something that starts off from the big picture. Can someone please help me get started?

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Could not load SWT library on Windows 32-bit

- by Firzen

I am almost done with one Java project that I have been developing on Linux. Now I need to build and test it on Windows. So I have installed Eclipse on Windows XP 32-bit, and imported my project. All dependencies of project are in jar files in lib folder, and on Linux everything works well, but on Windows XP I get following error: Exception in thread "main" java.lang.UnsatisfiedLinkError: Could not load SWT library. Reasons: no swt-pi-gtk-4234 in java.library.path no swt-pi-gtk in java.library.path Can't load library: C:\Documents and Settings\firzen\.swt\lib\win32\x86\swt-pi-gtk-4234.dll Can't load library: C:\Documents and Settings\firzen\.swt\lib\win32\x86\swt-pi-gtk.dll at org.eclipse.swt.internal.Library.loadLibrary(Library.java:331) at org.eclipse.swt.internal.Library.loadLibrary(Library.java:240) at org.eclipse.swt.internal.gtk.OS.<clinit>(OS.java:22) at org.eclipse.swt.internal.Converter.wcsToMbcs(Converter.java:63) at org.eclipse.swt.internal.Converter.wcsToMbcs(Converter.java:54) at org.eclipse.swt.widgets.Display.<clinit>(Display.java:133) at gui.Frontend.<init>(Frontend.java:51) at Fighter.main(Fighter.java:18) I have searched for these DLLs, but I have failed to find them. Where can I download these DLL files? Thanks in advance.

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Save/Load jFreechart TimeSeriesCollection chart from XML

- by IMAnis_tn

I'm working with this exemple wich put rondom dynamic data into a TimeSeriesCollection chart. My problem is that i can't find how to : 1- Make a track of the old data (of the last hour) when they pass the left boundary (because the data point move from the right to the left ) of the view area just by implementing a horizontal scroll bar. 2- Is XML a good choice to save my data into when i want to have all the history of the data? public class DynamicDataDemo extends ApplicationFrame { /** The time series data. */ private TimeSeries series; /** The most recent value added. */ private double lastValue = 100.0; public DynamicDataDemo(final String title) { super(title); this.series = new TimeSeries("Random Data", Millisecond.class); final TimeSeriesCollection dataset = new TimeSeriesCollection(this.series); final JFreeChart chart = createChart(dataset); final ChartPanel chartPanel = new ChartPanel(chart); final JPanel content = new JPanel(new BorderLayout()); content.add(chartPanel); chartPanel.setPreferredSize(new java.awt.Dimension(500, 270)); setContentPane(content); } private JFreeChart createChart(final XYDataset dataset) { final JFreeChart result = ChartFactory.createTimeSeriesChart( "Dynamic Data Demo", "Time", "Value", dataset, true, true, false ); final XYPlot plot = result.getXYPlot(); ValueAxis axis = plot.getDomainAxis(); axis.setAutoRange(true); axis.setFixedAutoRange(60000.0); // 60 seconds axis = plot.getRangeAxis(); axis.setRange(0.0, 200.0); return result; } public void go() { final double factor = 0.90 + 0.2 * Math.random(); this.lastValue = this.lastValue * factor; final Millisecond now = new Millisecond(); System.out.println("Now = " + now.toString()); this.series.add(new Millisecond(), this.lastValue); } public static void main(final String[] args) throws InterruptedException { final DynamicDataDemo demo = new DynamicDataDemo("Dynamic Data Demo"); demo.pack(); RefineryUtilities.centerFrameOnScreen(demo); demo.setVisible(true); while(true){ demo.go(); Thread.currentThread().sleep(1000); } } }

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How to load/save C++ class instance (using STL containers) to disk

- by supert

I have a C++ class representing a hierarchically organised data tree which is very large (~Gb, basically as large as I can get away with in memory). It uses an STL list to store information at each node plus iterators to other nodes. Each node has only one parent, but 0-10 children. Abstracted, it looks something like: struct node { public: node_list_iterator parent; // iterator to a single parent node double node_data_array[X]; map<int,node_list_iterator> children; // iterators to child nodes }; class strategy { private: list<node> tree; // hierarchically linked list of nodes struct some_other_data; public: void build(); // build the tree void save(); // save the tree from disk void load(); // load the tree from disk void use(); // use the tree }; I would like to implement the load() and save() to disk, and it should be fairly fast, however the obvious problems are: I don't know the size in advance; The data contains iterators, which are volatile; My ignorance of C++ is prodigious. Could anyone suggest a pure C++ solution please?

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Problem with using Jquery.ajax over .load on Zend

- by Matthew

Right now, what i'm trying to do is to replace a label on the front page with a block of html. Right now, the page basically has: <label id="replace"></label> the js currently has: $(document).ready(function(){ $("#replace").load('/test'); }); the Zend class function has: public function indexAction(){ $this->_helper->layout()->disableLayout(); $this->_view->message = "This is from TestController index"; } and finally the index.phtml template simply has: <?php echo $this->message;?> Right now, I want to change the code around so that instead of just replacing that label with the same message, it would do a POST where the function will pull out a parameter, do something (like for instance, go to the database and pull something out with the POST parameter) and then return the message. I've tried editing the js so that it would look like: $.post('/test', {param : "test_param"}, function(data) {$("#replace").html(data);}); or $.ajax({ type: 'POST', url: '/test', data: "{param:test_param}", contentType: "application/json; charset=utf-8", dataType: "json", success: function(data) {$("#replace").html(data);} }); and neither worked. I took a step back and tried to replicate the .load functionality and do: $.ajax({ url: '/test', success: function(data) { $('#replace').html(data); alert('Load was performed.'); } }); and it doesn't work either. Anyone have any tips on how to go about doing this?

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Handling primary key duplicates in a data warehouse load

- by Meff

I'm currently building an ETL system to load a data warehouse from a transactional system. The grain of my fact table is the transaction level. In order to ensure I don't load duplicate rows I've put a primary key on the fact table, which is the transaction ID. I've encountered a problem with transactions being reversed - In the transactional database this is done via a status, which I pick up and I can work out if the transaction is being done, or rolled back so I can load a reversal row in the warehouse. However, the reversal row will have the same transaction ID and so I get a primary key violation. I've solved this for now by negating the primary key, so transaction ID 1 would be a payment, and transaction ID -1 (In the warehouse only) would be the reversal. I have considered an alternative of generating a BIT column, where 0 is normal and 1 is reversal, then making the PK the transaction ID and the BIT column. My question is, is this a good practice, and has anyone else encountered anything like this? For reference, this is a payment processing system, so values will not be modified, so there will only ever be transactions and reversals.

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Lazy load images in UITableViewCell

- by lostInTransit

Hi I have some 50 custom cells in my UITableView. I want to display an image and a label in the cells where I get the images from URLs. I want to do a lazy load of images so the UI does not freeze up while the images are being loaded. I tried getting the images in separate threads but I have to load each image every time a cell becomes visible again (Otherwise reuse of cells shows old images) Apps like Facebook load images only for cells currently visible and once the images are loaded, they are not loaded again. Can someone please tell me how to duplicate this behavior. Thanks. Edit Trying to cache images in an NSMutableDictionary object creates problems when the user scrolls fast. I am getting images only when scrolling completely stops and clearing out the cache on memory warning. But the app invariably gets a memory warning (due to size of images being cached) and clears the cache before reloading. If scrolling is very fast, it crashes. Any other suggestions are welcome

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jQuery slider to load content one at a time

- by Barrett

I have a slider that load all of my content at once. Into a div. Like so: external page.php $get_users = mysql_query("SELECT * FROM user WHERE id!='$user_id'"); while ($rows = mysql_fetch_assoc($get_users)) { $id = $rows['id']; $firstname = $rows['firstname']; $display_info .= ' <div class="f_outer" id="' . $id . '"> <div class="f_name likeu">' . $firstname . '</div> </div>'; } echo $display_info; I call this page from my find.php page using bxslider Here is my find.php page below. <script type="text/javascript"> $(function() { var slider = $("#slider1").bxSlider(); $("#slider-like").live('click', function() { slider.goToNextSlide(); return false; }); }); </script> <div id="slider-like>Yes</div> <div id="slider1"> <?PHP include ("external.php"); ?> </div> So what I get is all of my .f_outer div on the find.php page. I have hundreds of user and they will all be loaded at once. I would like to only load one slide at a time. So when I click #slider-like it load one of my dive from my external page.

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NGINX access logging with subdomain

- by user353877

We are trying to log requests made through an nginx load balancer. When we make requests to our server on a subdomain (api.blah.com), the request does not show up in the access logs However, requests made directly to blah.com do show up in the access logs. CONFIGURATION INFO We have a DNS record that creates a CNAME for the subdomain 'api' TRIED SO FAR We have tried looking in nginx.conf for exclusions (or anything that would be telling it to not log) We have tried adding server entries with the subdomain specifically and telling those to log but nothing seems to make a difference

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How to make Nginx fire 504 immediately is server is not available?

- by Georgiy Ivankin

I have Nginx set up as a load balancer with cookie-based stickiness. The logic is: If the cookie is NOT there, use round-robbing to choose a server from cluster. If the cookie is there, go to the server that is associated with the cookie value. Server is then responsible for setting the cookie. What I want to add is this: If the cookie is there, but server is down, fallback to round-robbing step to choose next available server. So actually I have load balancing and want to add failover support on top of it. I have managed to do that with the help of error_page directive, but it doesn't work as I expected it to. The problem: 504 (and the fallback associated with it) fires only after 30s timeout even if the server is not physically available. So what I want Nginx to do is fire a 504 (or any other error, doesn't matter) immediately (I suppose this means: when TCP connection fails). This is the behavior we can see in browsers: if we go directly to server when it is down, browser immediately tells us that it can't connect. Moreover, Nginx seems to be doing this for 502 error: if I intentionally misconfigure my servers, Nginx fires 502 immediately. Configuration (stripped down to basics): http { upstream my_cluster { server 192.168.73.210:1337; server 192.168.73.210:1338; } map $cookie_myCookie $http_sticky_backend { default 0; value1 192.168.73.210:1337; value2 192.168.73.210:1338; } server { listen 8080; location @fallback { proxy_pass http://my_cluster; } location / { error_page 504 = @fallback; # Create a map of choices # see https://gist.github.com/jrom/1760790 set $test HTTP; if ($http_sticky_backend) { set $test "${test}-STICKY"; } if ($test = HTTP-STICKY) { proxy_pass http://$http_sticky_backend$uri?$args; break; } if ($test = HTTP) { proxy_pass http://my_cluster; break; } return 500 "Misconfiguration"; } } } Disclaimer: I am pretty far from systems administration of any kind, so there may be some basics that I miss here. EDIT: I'm interested in solution with standard free version of Nginx, not Nginx Plus. Thanks.

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How do I mirror a MySQL database?

- by user45745

I'm running two load balanced servers for one website, and I'd like the databases to be synchronized. Queries may be run on either of the two servers because they are both production sites, so the replication can't just work one way. It doesn't have to be in real-time, just fairly accurate so people don't notice a difference when they get switched to a different server.

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How to load models in the extended MY_Router class in codeigniter

- by askkirati

I am not able to load models to the extended My_Router class in codeigniter. Below is my code: class MY_Router extends CI_Router { function MY_Router() { parent::CI_Router(); } function _validate_request($segments) { // Does the requested controller exist in the root folder? if (file_exists(APPPATH.'controllers/'.$segments[0].EXT)) { return $segments; } // Is the controller in a sub-folder? if (is_dir(APPPATH.'controllers/'.$segments[0])) { // Set the directory and remove it from the segment array $this->set_directory($segments[0]); $segments = array_slice($segments, 1); if (count($segments) > 0) { // Does the requested controller exist in the sub-folder? if ( ! file_exists(APPPATH.'controllers/'.$this->fetch_directory().$segments[0].EXT)) { show_404($this->fetch_directory().$segments[0]); } } else { $this->set_class($this->default_controller); $this->set_method('index'); // Does the default controller exist in the sub-folder? if ( ! file_exists(APPPATH.'controllers/'.$this->fetch_directory().$this->default_controller.EXT)) { $this->directory = ''; return array(); } } return $segments; } // Let's check if there are category segments $category_routes = $this->category_routing($segments); if($category_routes !== FALSE) { return $category_routes; } $user_routes = $this->user_routing($segments); if($user_routes != FALSE) { return $user_routes; } show_404($segments[0]); } function category_routing($segments) { $this->load->model('category_model'); if($this->category_model->category_exist($segments[0])) { //if only category if(count($segments)==1) { return array('category', 'category_browse', $segments[0]); } //category pagination if(count($segments)==2 and is_numeric($segments[1])) { return array('category','category_browse', $segments[0], $segments[1]); } //category upcoming if(count($segments)==2 and $segments[1] == 'upcoming') { return array('category','upcoming', $segments[0]); } //category upcoming pagination if(count($segments)==3 and $segments[1] == 'upcoming' and is_numeric($segments[3])) { return array('category','upcoming', $segments[0], $segments[3]); } //category top if(count($segments)==3 and $segments[1] == 'top') { return array('category','top', $segments[0], $segments[2]); } //category top pagination if(count($segments)==4 and $segments[1] == 'top' and is_numeric($segments[3])) { return array('category','top', $segments[0], $segments[3]); } } return FALSE; } function user_routing($segments) { $this->load->model('dx_auth/users', 'user_model'); if($this->user_model->check_username($segments[0])) { //only profile if(count($segments)==1) { return array('user','profile',$segments[0]); } //all friends if(count($segments)==2 and $segment[1]=='allfriends') { return array('user','allfriends',$segments[0]); } //all subscribers if(count($segments)==2 and $segment[1]=='allsubscribers') { return array('user','allsubscribers',$segments[0]); } //all subscription if(count($segments)==2 and $segment[1]=='allsubscriptions') { return array('user','allsubscriptions',$segments[0]); } } return FALSE; } } I have tried loading the models by using get_instance function provided by codeigniter but seems like it doesnot work. All i need is load the models in extended system library.

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How can i connect two or more machines via tcp cable to form a network grid?

- by Gath

How can i connect two or more machines to form a network grid and how can i distribute work load to the two machines? What operating systems do i need to run on the machines, and what application should i use to manage the load balancing? NB: I read somewhere that google uses cheap machines to perform this fete, how do they connect two network cards( 'Teaming' ) and distribute load across the machines? Good practical examples would serve me good, with actual code samples. Pointers to some good site i might read this stuff will be highly appreciated.

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loading Data in VBA from a text file

- by omegayen

I am not very familiar with VBA but need to use it for a new software program I am using (not Microsoft related) I have a text file that has columns of data I would like to read into VBA. Specifically the text file has 4 entries per row. Thus I would like to load in the column vectors (N by 1). The text file is separated by a space between each entry. So for example I want to load in column one and save it as array A, then column two and save as array B, then column three and save as array C, and then column four and save as array D. This code snippet found below from http://www.tek-tips.com/faqs.cfm?fid=482 is something I found that can load in text to an array, but I need to adapt it to be able to save the columns as different arrays as specified above... Open "MyFile.txt" For Input As #1 ReDim Txt$(0) Do While Not EOF(1) ReDim Preserve Txt$(UBound(Txt$) + 1) Input #1, Txt$(UBound(Txt$)) Loop Close #1

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LVS TCP connection timeouts - lingering connections

- by Jon Topper

I'm using keepalived to load-balance connections between a number of TCP servers. I don't expect it matters, but the service in this case is rabbitmq. I'm using NAT type balancing with weighted round-robin. A client connects to the server thus: [client]-----------[lvs]------------[real server] a b If a client connects to the LVS and remains idle, sending nothing on the socket, this eventually times out, according to timeouts set using ipvsadm --set. At this point, the connection marked 'a' above correctly disappears from the output of netstat -anp on the client, and from the output of ipvsadm -L -n -c on the lvs box. Connection 'b', however, remains ESTABLISHED according to netstat -anp on the real server box. Why is this? Can I force lvs to properly reset the connection to the real server?

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Is the W3 standard a major factor when google decides SERP position?

- by Camran

I have a dynamic php website which index only has around 800 errors according to the w3 validator online. I have tried checking major websites like ebay, stackoverflow and others also, all with around 400 errors. So my first thought is, what good is that validator when it always displays errors? Secondly, will the errors affect my SERP ranking? ie, will me fixing these errors as good as I can increase my Google search position? Thanks

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Fortigate - Accessing a Virtual Server address from several interfaces

- by Jeremy G

I am setting up a new application in its own DMZ on our Fortigate 300C firewalls. I have defined a load-balancing configuration for part of the application, and this works fine for traffic coming in from our internal network. However, I would also like this application to be reachable from other DMZs, for inter-application traffic, and from the SSL VPN interface. I can't seem to define the required policy, and it seems this is due to Virtual Servers being bound to the client interface on the Fortigate rather than the server interface (and so my virtual IP is not accessible from any of these other interfaces) Does anyone have an idea how I might go about this ? I guess I could create other virtual IPs for each interface, but this gets complicated to handle as clients need to change the address they use depending on how they are connecting. Thanks, Jeremy G

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scalability with nginx, passenger, ruby on rails setup

- by Dani Cela

Hey guys I had a question regarding scalability for my RoR application. We have been optimizing our application over the last few days and after running blitz.io, notice that our application times out after maybe 1000 hits in 30 seconds we experienced massive timeouts. In the 1 minute test apparently 74% of users would have timed out. Look at the performance of my website: http://blitz.io/report/1c8eb2f395a5eadeabd62fd831ada9e5 Not saying that our website will in any way experience this now, but I wish to design the infrastructure to handle this. What is normally done in this situation? Currently we have one web server and one database server. Would load balancing be the route to go?

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loadbalancing with difference nginx location context and backend server context

- by robinmag

Hi, I used nginx and upstream module for load balancing with the following config upstream lb { server 127.0.0.1:8080; server 127.0.0.1:8081; } server { listen 88; server_name localhost; location /cas/ { proxy_pass http://lb; proxy_redirect off; proxy_connect_timeout 2; proxy_set_header Host $host; proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; } } the problem is the "location /context/" have to match to the context of backend server so when i request localhost/context/index.html then nginx routes it to 127.0.0.1:8080/context/index.html or 127.0.0.1:8080/context/index.html. Is it possible to have difference backend context and nginx location for example with "location /" nginx will routes the request to 127.0.0.1:8080/context/index.html or 127.0.0.1:8080/context/index.html Thank you.

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loadbalancing with difference nginx location context and backend context

- by robinmag

Hi, I used nginx and upstream module for load balancing with the following config upstream lb { server 127.0.0.1:8080; server 127.0.0.1:8081; } server { listen 88; server_name localhost; location /cas/ { proxy_pass http://lb; proxy_redirect off; proxy_connect_timeout 2; proxy_set_header Host $host; proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; } } the problem is the "location /context/" have to match to the context of backend server so when i request localhost/context/index.html then nginx routes it to 127.0.0.1:8080/context/index.html or 127.0.0.1:8080/context/index.html. Is it possible to have difference backend context and nginx location for example with "location /" nginx will routes the request to 127.0.0.1:8080/context/index.html or 127.0.0.1:8080/context/index.html Thank you.

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Looking for the best ec2 setup for 3 sites totaling in 1.5 mil in traffic monthly

- by john h.

I am looking to consolidate our current aws setup of 2 Large ubuntu ec2 servers and 2 large RDS server for our 3 websites that have a total of about 1.5 million hits a month and increasing every month with the majority of traffic (1 mil) to one forum site in the group and the rest of traffic to an ecommerce site and a small wordpress site. So here is my question/thought? Would it be better for us to combine the two ec2 large servers to just one and same with the 2 RDS servers so we run all three sites off one large ec2 and one RDS. -or- Should we setup maybe 2-3 smaller ec2 servers load balenced and a single RDS. -or- Something completely different setup? One concern is that if one site crashes it takes with it the others. It happened in the past but I am pretty sure its because of the forum software and not the server setup. -john

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Can I use nginx to start EC2 instances on demand?

- by Gabe Hollombe

TL;DR - Is there a way to make nginx act as an elastic load balancer that will spin up EC2 instances on demand, allowing for the case when periods of no demand mean no instances will be running? Longer explanation - I have an nginx server that proxy_pass'es requests to a server on EC2. This server doesn't get many requests, so I'd like to keep the server spun down during periods of inactivity (I already have a script to do this). Then, when the instance is spun down and nginx gets a request for that instance, it will time out when trying to get a response from it. At this point, can I somehow trigger a shell command on the server to use EC2's command line tools to spin up the instance, then re-try the user's request after it has started?

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Loadbalance UDP traffic with session affinity and way to take servers in & out of rotation

- by William

What is the best way to go about load balancing UDP traffic among a whole bunch of servers, while keeping session affinity based on the users' IP? I need to also be able to take servers in and out of rotation for new clients, so when they join for the first time, they get put on a server in a list of available servers, and clients already connected would stay connected to their specific server. I have written the software to maintain a list, but I can't seem to find anything that would perform this functionality. If you need the context, this is to facilitate game tournaments for Minecraft: Pocket Edition, which is done with UDP traffic, I cannot change the protocol. And, because tournaments open and close, I need to be able to place players on their proper servers. Performance is also a priority, I have a program to do this but it is very bloated and slow. Thanks for any help! William

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LVS TCP connection timeouts - lingering connections

- by Jon Topper

I'm using keepalived to load-balance connections between a number of TCP servers. I don't expect it matters, but the service in this case is rabbitmq. I'm using NAT type balancing with weighted round-robin. A client connects to the server thus: [client]-----------[lvs]------------[real server] a b If a client connects to the LVS and remains idle, sending nothing on the socket, this eventually times out, according to timeouts set using ipvsadm --set. At this point, the connection marked 'a' above correctly disappears from the output of netstat -anp on the client, and from the output of ipvsadm -L -n -c on the lvs box. Connection 'b', however, remains ESTABLISHED according to netstat -anp on the real server box. Why is this? Can I force lvs to properly reset the connection to the real server?

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Round-Robin DNS in mobile networks

- by k7k0

After reading load distribution alternatives and giving my limited skills on the area I'm biased toward round-robin DNS strategy. From what I understood, one key aspect of DNS Round-Robin is setting a low TTL value, avoiding caching. My main concern is that all my traffic comes from mobile networks, almost 30% of that comes from t-mobile 3G. Some questions: 1) Is there a chance that almost all clients on the same mobile network will be redirected to the same IP in the TTL frame? That would kill the distribution technique. 2) If I choose a really low TTL (zero or one). That impacts directly over client performance? It does a DNS miss every time or it's a setting that only impacts on DNS servers? Any help would be much appreciated. Thanks

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