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  • Retrieving license type (linux/windows/windows+sqlserver) for an Amazon EC2 instance via the API?

    - by Geir
    I need to calculate the hourly running costs for my Amazon EC2 instances. This varies even between instances with same hardware configs (instance types) because I use different amazon images (AMIs): some plain windows server and some windows server with sql server (both of them have additional costs compared with plain linux instances) The EC2 Java API has a describeInstances() method which returns Instance objects with metadata such as instance id, instance type (m1.small/large...), state (running,stopped..) public ip, etc. This Instance object also has a .getLicense().getPool() which according to the Java API should return "The license pool from which this license was used (ex: 'windows')." I thought this is were it may also give 'windows+sqlserver' or something to that effect. The getLicense() method does however return null.. I've navigated around the EC2 web console, not being able to find this information, but I'm hoping that it is possible - otherwise it would mean that you cannot identify the true hourly cost of an particular instance unless you know which AMI was used to create it in the first place (plain windows server or windows server with sql server). Anyone? Thanks :) /Geir

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  • How to make multiple Excel files open in ONE window/instance of Excel 2003 in Win 7

    - by Mark
    I'm running Excel 2003 on my new Windows 7 machine. (There is also a Excel 2010 starter pre installed that I do not use). I'm a heavy user of Excel. I use it all day every day. I often have 10 or 15 sheets open and once and many of them have cell references to each other. I also have a macro file that keeps all my short cuts. On my old W2K machine when I clicked on a .xls file or a shortcut to one to it would open that file in the existing instance of Excel. This is as it should be. I would have many files open, in only one "window" or instance of Excel. All the files could interact with each other, the cross file lookups worked, my macros worked and I could switch between workbooks with CTRL Tab or CTRL F6, I could move tabs from one workbook to another. On the new W7 machine clicking on an icon opens a NEW INSTANCE of Excel every time. This is terribly frustrating. None of my connecting spreadsheets work anymore. My macros don't work. I can't connect files, I can't move tabs. I'm stuck. I can't do my work! I can still open files in one instance by doing a CTRL-O and navigating, but I need to my files to work on a click. I'm guessing this is a flaw in the registry files, possibly because of the starter Excel 2010 that came preloaded on my new machine. Can you walk me through a registry edit to fix this bug? Is there an easier way than a registry edit?

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  • How can I make apt-get wait for another instance to finish?

    - by rajagenupula
    Is there any way I can make apt-get wait for the other apt-get (or similar) processes to finish? I know that, generally, apt-get can only one instance at a time and if we try to run apt-get at the same time then we get a message saying that some other process is using it. My question is: how can I make apt-get wait for the other processes to finish and then run? Advantage: No need to type the command apt-get again, it will be automated after the 1st apt-get finishes.

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  • How to set IP address of Amazon EC2 instance to its Elastic IP?

    - by TWord
    Hi, I have an Amazon EC2 instance running and I am installing a program on it that needs to know what the machine's IP address is. Can I set the Elastic IP address to the IP address within the EC2 instance? Its okay if it reroutes data packets somewhere 'outside' and then back to itself, but the software NEEDs me to specify an IP address of the machine its on. I proceeded with the software installation using the "local IP" (10.xx.xx.xx) within the software installation. I don't know if this is the reason why the application is not visible publicly (as I'm trying to determine in the question http://serverfault.com/questions/166946/allowing-web-access-to-an-amazon-ec2-windows-server-2008-instance-running-tomcat)

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  • SQL ERROR: Verify that the instance name is correct and that SQL Server is configured to allow remote connections?

    - by scepak
    I am getting following error while connecting to my local Sql Express. An error has occurred. Details of the exception: A network-related or instance-specific error occurred while establishing a conne ction to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Serve r/Instance Specified) Unable to connect to SQL Server database. I am able to connect to Sql Server using Management Studio.

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  • What's the difference between instance and server process in Oracle database.

    - by Summer_More_More_Tea
    Hi folks: I'm now getting familiar with Oracle database. Unfortunately, I'm puzzled by the concept instance and server process. My question is what's the difference between instance and server process. What's more, what's the life cycle of instance and server process respectively? My textbook at hand is about Oracle 9i, which doesn't give me a clear explanation. Any reply will be appreciated. Thanks in advance. Kind regards!

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  • C#: System.Lazy&lt;T&gt; and the Singleton Design Pattern

    - by James Michael Hare
    So we've all coded a Singleton at one time or another.  It's a really simple pattern and can be a slightly more elegant alternative to global variables.  Make no mistake, Singletons can be abused and are often over-used -- but occasionally you find a Singleton is the most elegant solution. For those of you not familiar with a Singleton, the basic Design Pattern is that a Singleton class is one where there is only ever one instance of the class created.  This means that constructors must be private to avoid users creating their own instances, and a static property (or method in languages without properties) is defined that returns a single static instance. 1: public class Singleton 2: { 3: // the single instance is defined in a static field 4: private static readonly Singleton _instance = new Singleton(); 5:  6: // constructor private so users can't instantiate on their own 7: private Singleton() 8: { 9: } 10:  11: // read-only property that returns the static field 12: public static Singleton Instance 13: { 14: get 15: { 16: return _instance; 17: } 18: } 19: } This is the most basic singleton, notice the key features: Static readonly field that contains the one and only instance. Constructor is private so it can only be called by the class itself. Static property that returns the single instance. Looks like it satisfies, right?  There's just one (potential) problem.  C# gives you no guarantee of when the static field _instance will be created.  This is because the C# standard simply states that classes (which are marked in the IL as BeforeFieldInit) can have their static fields initialized any time before the field is accessed.  This means that they may be initialized on first use, they may be initialized at some other time before, you can't be sure when. So what if you want to guarantee your instance is truly lazy.  That is, that it is only created on first call to Instance?  Well, there's a few ways to do this.  First we'll show the old ways, and then talk about how .Net 4.0's new System.Lazy<T> type can help make the lazy-Singleton cleaner. Obviously, we could take on the lazy construction ourselves, but being that our Singleton may be accessed by many different threads, we'd need to lock it down. 1: public class LazySingleton1 2: { 3: // lock for thread-safety laziness 4: private static readonly object _mutex = new object(); 5:  6: // static field to hold single instance 7: private static LazySingleton1 _instance = null; 8:  9: // property that does some locking and then creates on first call 10: public static LazySingleton1 Instance 11: { 12: get 13: { 14: if (_instance == null) 15: { 16: lock (_mutex) 17: { 18: if (_instance == null) 19: { 20: _instance = new LazySingleton1(); 21: } 22: } 23: } 24:  25: return _instance; 26: } 27: } 28:  29: private LazySingleton1() 30: { 31: } 32: } This is a standard double-check algorithm so that you don't lock if the instance has already been created.  However, because it's possible two threads can go through the first if at the same time the first time back in, you need to check again after the lock is acquired to avoid creating two instances. Pretty straightforward, but ugly as all heck.  Well, you could also take advantage of the C# standard's BeforeFieldInit and define your class with a static constructor.  It need not have a body, just the presence of the static constructor will remove the BeforeFieldInit attribute on the class and guarantee that no fields are initialized until the first static field, property, or method is called.   1: public class LazySingleton2 2: { 3: // because of the static constructor, this won't get created until first use 4: private static readonly LazySingleton2 _instance = new LazySingleton2(); 5:  6: // Returns the singleton instance using lazy-instantiation 7: public static LazySingleton2 Instance 8: { 9: get { return _instance; } 10: } 11:  12: // private to prevent direct instantiation 13: private LazySingleton2() 14: { 15: } 16:  17: // removes BeforeFieldInit on class so static fields not 18: // initialized before they are used 19: static LazySingleton2() 20: { 21: } 22: } Now, while this works perfectly, I hate it.  Why?  Because it's relying on a non-obvious trick of the IL to guarantee laziness.  Just looking at this code, you'd have no idea that it's doing what it's doing.  Worse yet, you may decide that the empty static constructor serves no purpose and delete it (which removes your lazy guarantee).  Worse-worse yet, they may alter the rules around BeforeFieldInit in the future which could change this. So, what do I propose instead?  .Net 4.0 adds the System.Lazy type which guarantees thread-safe lazy-construction.  Using System.Lazy<T>, we get: 1: public class LazySingleton3 2: { 3: // static holder for instance, need to use lambda to construct since constructor private 4: private static readonly Lazy<LazySingleton3> _instance 5: = new Lazy<LazySingleton3>(() => new LazySingleton3()); 6:  7: // private to prevent direct instantiation. 8: private LazySingleton3() 9: { 10: } 11:  12: // accessor for instance 13: public static LazySingleton3 Instance 14: { 15: get 16: { 17: return _instance.Value; 18: } 19: } 20: } Note, you need your lambda to call the private constructor as Lazy's default constructor can only call public constructors of the type passed in (which we can't have by definition of a Singleton).  But, because the lambda is defined inside our type, it has access to the private members so it's perfect. Note how the Lazy<T> makes it obvious what you're doing (lazy construction), instead of relying on an IL generation side-effect.  This way, it's more maintainable.  Lazy<T> has many other uses as well, obviously, but I really love how elegant and readable it makes the lazy Singleton.

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  • Running TeamCity from Amazon EC2 - Cloud based scalable build and continuous Integration

    - by RoyOsherove
    I’ve been having fun playing with the amazon EC2 cloud service. I set up a server running TeamCity, and an image of a server that just runs a TeamCity agent. I also setup TeamCity  to automatically instantiate agents on EC2 and shut them down based upon availability of free agents. Here’s how I did it: The first step was setting up the teamcity server. Create an account on amazon EC2 (BTW, amazon’s sites works better in IE than it does in chrome.. who knew!?) Open the EC2 dashboard, and click “Launch Instance” . From the “Quick Start” tab I selected from the list: “Getting Started on Microsoft Windows Server 2008 (AMI Id: ami-c5e40dac)” .  it’s good enough to just run teamcity. In the instance details, I used the default (Small instance, 1.7 GB mem). You might want to choose a close availability zone based on where you are. We want to “Launch instances” so click continue. Select the default kernel, RAM disk and all. No need to enable monitoring for now (you can do that later). click continue. If you don’t have a key pair, you will be prompted to create one. Once you do, select it in the list. Now you’ll be prompted to create a security group. I named mine “TC” as in “TeamCity”. each group is a bunch of settings on which ports can be let through into and out of a hosted machine.  keep it as the default settings. We will change them later. Click continue,  review and then click “Launch”. Now you’ll be able to see the new instance in the running instances list on your site. Now, you need to install stuff on that instance (TeamCity!) . To do that, you’ll need to Remote desktop into that instance. To do that, we’ll get the admin password for that instance: Check it on the list, and click “Instance Actions” - “Get Windows Admin Password”. You might have to wait about 10 minutes or so for the password to be generated for you. Once you have the password, you will remote desktop (start-run-‘mstsc’) into the instance. It’s address is a dns address shown below the list under “Public DNS”. it looks something like: ec2-256-226-194-91.compute-1.amazonaws.com Once you’re inside the instance – you’ll need to open IE (it is in hardened mode so you’ll have to relax its security settings to download stuff). I first downloaded chrome and using chrome I downloaded TeamCity. Note that the download speed is FAST. several MBs per second. To be able to see TeamCity from the outside, you will need to open the advanced firewall settings inside the remote machine, and add incoming and outgoing rules for port 80 (HTTP). Once you do that, you should be able to see the machine from the outside. If you still can’t, see the next step. I also enabled ports 9090 since I will use this machine to create an agent image later as well. Now configure the security group (TC) to enable talking to agents: IN the EC2 dashboard click on “Security Groups” and select your group. To add a rule, click on the empty list under the ‘protocol’ header. select TCP. from and ‘to’ ports are 9090. source ip is 0.0.0.0/0 (every ip is allowed). click “Save.  Also make sure you can see “HTTP” tcp 80 in that list. if you can’t see it, add it or you won’t be able to browse to the machine’s teamcity server home page. I also set an elastic IP for the machine: so I always have the same IP for the machine instance. Allocate and set one through the”Elastic IP” link on the EC2 dashboard.   you should now have a working instance of teamcity.   Now let’s create an agent image. Repeat steps 1-9, but this time, make sure you select a machine that fits what an agent might do. I selected Instance type – Hihg-CPU medium machine,  that is much faster. On that machine, I installed what I needed (VS 2010, PostSharp etc..). downloading VS 2010 from MSDN (2 GB took less than 10 min!) Now, instead of installing teamcity, browse using the browser to the teamcity homepage (from within the remote machine). go to the Administration page, and click the upper right link “Install agents”. Install the agent on he local machine – set it to the IP or DNS of the running TeamCity server. That way you’ll be able to check their connectivity live before making this machine your official agent image to reuse. Once the agent is installed, see that the TC server can see it and use it. see steps 13-14 above if they can’t. Once it works, you can take steps to make this image your agent image to be reused. next, here is a copy-paste of several steps to take from http://confluence.jetbrains.net/display/TCD5/Setting+Up+TeamCity+for+Amazon+EC2 Configure system so that agent it is started on machine boot (and make sure TeamCity server is accessible on machine boot). Test the setup by rebooting machine and checking that the agent connects normally to the server. Prepare the Image for bundling: Remove any temporary/history information in the system. Stop the agent (under Windows stop the service but leave it in Automatic startup type) Delete content agent logs and temp directories (not necessary) Delete "<Agent Home>/conf/amazon-*" file (not necessary) Change config/buildAgent.properties to remove properties: name, serverAddress, authToken (not necessary)   Now, we need to: Make AMI from the running instance. Configure TeamCity EC2 support on TeamCity server. Making an AMI: Check the instance of the agent in the EC2 dashboard instance list, and select instance actions->Create Image (EBS AMI) you’ll see the image pending in the APIs list in the EC2 dashboard. this could take 30 minutes or more. meanwhile we can configure the could support in the teamcity server. COPY THE AMI ID to the clipboard (looks like ami-a88aa4ce) Configuring TeamCity for Cloud: In TeamCity, click on “Agents” and then on “Cloud” tab. this is where you will control your cloud agents. to configure new cloud agents based on APIs, click on the right link to the “configuration page” Create a new profile and select AMazon EC2 as cloud type. Use your AMI ID that you copied to the clipboard into the “Images” field. Select an availability zone that is the same as the one your instance is running on for best communication perf between them make sure you select the ‘TC’ security group hopefully, that should be it, and teamcity will try to instantiate new instances on demand. Note that it may take around 10 minutes for an agent to become available to teamcity from the time it’s started.

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  • SOA & BPM Best of Oracle OpenWorld 2011

    - by JuergenKress
    Oracle OpenWorld 2011 is over – what important updates did you miss? Keynotes: Best of Oracle OpenWorld keynotes and general session is available on-demand: " + __flash__argumentsToXML(arguments,0) + "")); }' s_getswfurl='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' s_getcharset='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' s_getversion='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' s_getmovieid='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' s_getpageurl='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' s_getpagename='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' s_getaccount='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' s_gettrackclickmap='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' s_getdomindex='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' onomnitureunload='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' We recommend to watch: Oracle Cloud Computing Larry Ellison, CEO, Oracle Watch full-length keynote   Middleware General Session Hasan Rizvi, SVP, Oracle Watch full-length general session Presentations: All presentations are available online at the OpenWorld Content Catalog Product highlight: Was to launch of BPM Suite 11.1.1.5 Feature Pack Released and the Oracle Process Accelerators. For details please visit the Oracle BPM team blog and the Oracle SOA team blog.

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  • Why "object reference not set to an instance of an object" doesn't tell us which object?

    - by Saeed Neamati
    We're launching a system, and we sometimes get the famous exception NullReferenceException with the message Object reference not set to an instance of an object. However, in a method where we have almost 20 objects, having a log which says an object is null, is really of no use at all. It's like telling you, when you are the security agent of a seminar, that a man among 100 attendees is a terrorist. That's really of no use to you at all. You should get more information, if you want to detect which man is the threatening man. Likewise, if we want to remove the bug, we do need to know which object is null. Now, something has obsessed my mind for several months, and that is: Why .NET doesn't give us the name, or at least the type of the object reference, which is null?. Can't it understand the type from reflection or any other source? Also, what are the best practices to understand which object is null? Should we always test nullability of objects in these contexts manually and log the result? Is there a better way?

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  • fglrx: No matching Device section for instance... found how to fix it?

    - by Lejo
    I have HD 4850 card, Ubuntu 12.10 and installed legacy drivers using makson96 ppa. The issue is, that FGLRX can not detect my device and loads vesa bios. I had the same problem on ubuntu 11.10, 12.04 versions. I want to manually help fglrx find a matching device to load as it shoudld do. It is interesting, why does fglrx search for a device in a PCI:0@1:0:1 Bus? in xorg.cof different bus is indicated: Section "Device" Identifier "aticonfig-Device[0]-0" Driver "fglrx" BusID "PCI:1:0:0" EndSection fglrxinfo display: :0.0 screen: 0 OpenGL vendor string: Advanced Micro Devices, Inc. OpenGL renderer string: ATI Radeon HD 4800 Series OpenGL version string: 3.3.11653 Compatibility Profile Context Here is a part of my xorg log: [ 3.846] (II) VESA: driver for VESA chipsets: vesa [ 3.846] (II) FBDEV: driver for framebuffer: fbdev [ 3.846] (++) using VT number 7 [ 3.846] (WW) Falling back to old probe method for fglrx [ 3.883] (II) Loading PCS database from /etc/ati/amdpcsdb [ 3.883] (--) Assigning device section with no busID to primary device [ 3.883] (--) Chipset Supported AMD Graphics Processor (0x9442) found [ 3.884] (WW) fglrx: No matching Device section for instance (BusID PCI:0@1:0:1) found [ 3.884] (II) AMD Video driver is running on a device belonging to a group targeted for this release [ 3.884] (II) AMD Video driver is signed [ 3.884] (II) fglrx(0): pEnt->device->identifier=0xb7791d8f [ 3.884] (WW) Falling back to old probe method for vesa [ 3.884] (WW) Falling back to old probe method for fbdev from lispci i foud out finally, that my video card is in 01:00.0 slot. logically, if fglrx searches for a vdeo card device in a wrong place, it will not find it. 01:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI RV770 [Radeon HD 4850] Thanks in advance.

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  • Generating/managing config files for hosted application

    - by mfinni
    I asked a question about config management, and haven't seen a reply. It's possible my question was too vague, so let's get down to brass tacks. Here's the process we follow when onboarding a new customer instance into our hosted application : how would you manage this? I'm leaning towards a Perl script to populate templates to generate shell scripts, config files, XML config files, etc. Looking briefly at CFengine and Chef, it seems like they're not going to reduce the amount of work, because I'd still have to manually specify all of the changes/edits within the tool. Doesn't seem to be much of a gain over touching the config files directly. We add a stanza to the main config file for the core (3rd-party) application. This stanza has values that defines the instance (customer) name the TCP listener port for this instance (not one currently used) the DB2 database name (serial numeric identifier, already exists, they get prestaged for us by the DBAs) three sub-config files, by name - they need to be created from 3 templates and be named after the instance The sub-config files define: The filepath for the DB2 volumes The filepath for the storage of objects The filepath for just one of the DB2 volumes (yes, redundant to the first item. We run some application commands, start the instance We do some LDAP thingies (make an OU for the instance, etc.) We add a stanza to the config file for our security listener that acts as a passthrough to LDAP instance name LDAP OU TCP port for instance DB2 database name We restart the security listener (off-hours), change the main config file from item 1, stop and restart the instance. It is now authenticating via LDAP. We add the stop and start commands for this instance to the HA failover scripts. We import an XML config file into the instance that defines things for the actual application for the customer - user names, groups, permissions, and business rules. The XML is supplied by the implementation team. Now, we configure the dataloading application We add a stanza to the existing top-level config file that points to a new customer-level config file. The new customer-level config file includes: the instance (customer) name the DB2 database name arbitrary number of sub-config files, by name Each of the sub-config files defines: filepaths to the directories for ingestion, feedback, backup, and failure those filepaths have a common path to a customer-specific folder, and then one folder for each sub-config file Each of those filepaths needs to be created We need to add this customer instance to our monitoring scripts that confirm the proper processes are running and can be logged into. Of course, those monitoring config files include the instance name, the TCP port, the DB2 database name, etc. There's also a reporting application that needs to be configured for the new instance. You get the idea. There's also XML that is loaded into WAS by the middleware team. We give them the values for them to plug into the XML - they could very easily hand us the template and we could give them back completed XML.

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  • Multiple MySQL instances via mysqlmanager under Debian

    - by Karolis T.
    Has anyone got multiple MySQL instances running on Debian with mysqlmanager? Problem is, Debian doesn't ship with init.d script that takes mysqlmanager into account. Oh, and it doesn't work for me. I'm trying to run 3 instances, here's what I get after starting mysqlmanager # mysqlmanager --defaults-file=/etc/mysql/my.cnf ... 090614 0:42:10 starting instance 'mysqld2'... 090614 0:42:10 guardian: starting instance 'mysqld1'... 090614 0:42:10 starting instance 'mysqld1'... 090614 0:42:10 starting instance 'mysqld3'... 090614 0:42:10 guardian: starting instance 'mysqld3'... 090614 0:42:10 guardian: starting instance 'mysqld2'... 090614 0:42:10 starting instance 'mysqld2'... 090614 0:42:10 guardian: starting instance 'mysqld1'... 090614 0:42:10 starting instance 'mysqld1'... ... It just keeps "starting" and "restarting", but no MySQL instance ever starts up.

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  • How to open a pdf or a djvu on an specific instance of a document viewer?

    - by ciro
    I want using any free Linux document viewer that does both pdf and djvu (Okular, Evince, etc.) to do the following: magic_command('document-viewer','./11.pdf','instance1') magic_command('document-viewer','./21.djvu','instance2') two instances (windows) of document-viewer are opened one with 11.pdf and the other with 21.djvu then: magic_command('document-viewer','./12.djvu','instance1') magic_command('document-viewer','./22.pdf','instance2') the first instance (window) of document-viewer loads 12.djvu the second instance (window) of document-viewer loads 22.pdf

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  • Small website on Amazon EC2 Linux: a single large instance or more small instances in load balancing?

    - by Enrico Detoma
    I need to run a small website with a JSON webservice on Amazon EC2 Linux. The largest number of requests come from the JSON webservice, which provides some load in terms of MySQL queries. I'm trying to decide between two choices: A single large instance (Ubuntu 12.04 64-bit) with full LAMP stack or One or two small instances (Ubuntu 12.04 64-bit) with Apache/PHP only One small instance dedicated to MySQL (or RDS) Which setup would you consider to be more performant?

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  • What's the easiest way to auto-backup an EC2 instance?

    - by ripper234
    I have an EBS-backed Amazon EC2 instance. I would like to create a daily backup schedule, and keep, say, a week's worth of daily backups, plus a few older images (from 2,3,4 weeks ago). I don't mind creating the backups on the fly, with the snapshot mechanism, but I would like an easy wrapper to manage it for me. What is the simplest way to set this up? How much would this cost me, for a micro instance?

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  • List of Django model instance foreign keys losing consistency during state changes.

    - by Joshua
    I have model, Match, with two foreign keys: class Match(model.Model): winner = models.ForeignKey(Player) loser = models.ForeignKey(Player) When I loop over Match I find that each model instance uses a unique object for the foreign key. This ends up biting me because it introduces inconsistency, here is an example: >>> def print_elo(match_list): ... for match in match_list: ... print match.winner.id, match.winner.elo ... print match.loser.id, match.loser.elo ... >>> print_elo(teacher_match_list) 4 1192.0000000000 2 1192.0000000000 5 1208.0000000000 2 1192.0000000000 5 1208.0000000000 4 1192.0000000000 >>> teacher_match_list[0].winner.elo = 3000 >>> print_elo(teacher_match_list) 4 3000 # Object 4 2 1192.0000000000 5 1208.0000000000 2 1192.0000000000 5 1208.0000000000 4 1192.0000000000 # Object 4 >>> I solved this problem like so: def unify_refrences(match_list): """Makes each unique refrence to a model instance non-unique. In cases where multiple model instances are being used django creates a new object for each model instance, even if it that means creating the same instance twice. If one of these objects has its state changed any other object refrencing the same model instance will not be updated. This method ensure that state changes are seen. It makes sure that variables which hold objects pointing to the same model all hold the same object. Visually this means that a list of [var1, var2] whose internals look like so: var1 --> object1 --> model1 var2 --> object2 --> model1 Will result in the internals being changed so that: var1 --> object1 --> model1 var2 ------^ """ match_dict = {} for match in match_list: try: match.winner = match_dict[match.winner.id] except KeyError: match_dict[match.winner.id] = match.winner try: match.loser = match_dict[match.loser.id] except KeyError: match_dict[match.loser.id] = match.loser My question: Is there a way to solve the problem more elegantly through the use of QuerySets without needing to call save at any point? If not, I'd like to make the solution more generic: how can you get a list of the foreign keys on a model instance or do you have a better generic solution to my problem? Please correct me if you think I don't understand why this is happening.

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  • How can I make a Maybe-Transformer MaybeT into an instance of MonadWriter?

    - by martingw
    I am trying to build a MaybeT-Transformer Monad, based on the example in the Real World Haskell, Chapter Monad Transformers: data MaybeT m a = MaybeT { runMT :: m (Maybe a) } instance (Monad m) => Monad (MaybeT m) where m >>= f = MaybeT $ do a <- runMT m case a of Just x -> runMT (f x) Nothing -> return Nothing return a = MaybeT $ return (Just a) instance MonadTrans MaybeT where lift m = MaybeT $ do a <- m return (Just a) This works fine, but now I want to make MaybeT an instance of MonadWriter: instance (MonadWriter w m) => MonadWriter w (MaybeT m) where tell = lift . tell listen m = MaybeT $ do unwrapped <- listen (runMT m) return (Just unwrapped) The tell is ok, but I can't get the listen function right. The best I could come up with after 1 1/2 days of constructor origami is the one you see above: unwrapped is supposed to be a tuple of (Maybe a, w), and that I want to wrap up in a Maybe-Type and put the whole thing in an empty MonadWriter. But the compiler complains with: Occurs check: cannot construct the infinite type: a = Maybe a When generalising the type(s) for `listen' In the instance declaration for `MonadWriter w (MaybeT m)' What am I missing?

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  • How to remove multiple instances and just have one instance while multiple function calls in php ?

    - by Rachel
    public function getHelperInstance() { $user = new Helper(); $user->set($result['data']); return $user; } I am calling getHelper() class multiple times and if $user is not empty than am calling getHelperInstance(), now in my case getHelperInstance() always creates a new instance of Helper() class and so every time I call getHelperInstance() function am creating a new instance of Helper() so is there any way where can I can just create one instance of Helper() and use it multiple times instead of creating a new instance everytime. Any suggestions !!! public function getHelper() { $user = array(); if (!empty($user)) { $user = $this->getHelperInstance(); } return $user; }

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  • How to implement a single instance app manager in java (CVM PhoneME)?

    - by Marcus
    Hi, I'm working on a application manager for embeded platform based on the CVM PhoneME VM. The VM is started by a C++ app which configures the CVM and then triggers the VM itself. This C++ app is called form the command line passing the main class name and the classpath of a java application. There is a main java app (lets call it Manager) which loads the app using classloaders. I want this manager to be a single instance application so it could track all running apps. In other words: The first time I start an app (app1 for instance), the VM will launch and the Manager will load the app1. In further calls to load other apps (app2, app3 and so on), the same instance of the Manager would load those apps. The manager is working fine, except for the fact that this is not a single instance. Is it possible to do what I want? I found this: http://www.knowledgesutra.com/forums/topic/59760-how-to-implement-single-instance-application-on-java/ This is almost the same I want, except for the app loading part. However, the necessary packages are not available in the CVM implementation. Thanks very much.

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