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• SSH Login to an EC2 instance failing with previously working keys...

  - by Matthew Savage

  We recently had an issues where I had rebooted our EC2 instance (Ubuntu x86_64, version 9.10 server) and due to an EC2 issue the instance needed to be stopped and was down for a few days. Now I have been able to bring the instance back online I cannot connect to SSH using the keypair which previously worked. Unfortunately SSH is the only way to get into this server, and while I have another system running in its place there are a number of things I would like to try and retrieve from the machine. Running SSH in verbose mode yields the following: [Broc-MBP.local]: Broc:~/.ssh ? ssh -i ~/.ssh/EC2Keypair.pem -l ubuntu ec2-xxx.compute-1.amazonaws.com -vvv OpenSSH_5.2p1, OpenSSL 0.9.8l 5 Nov 2009 debug1: Reading configuration data /Users/Broc/.ssh/config debug1: Reading configuration data /etc/ssh_config debug2: ssh_connect: needpriv 0 debug1: Connecting to ec2-xxx.compute-1.amazonaws.com [184.73.109.130] port 22. debug1: Connection established. debug3: Not a RSA1 key file /Users/Broc/.ssh/EC2Keypair.pem. debug2: key_type_from_name: unknown key type '-----BEGIN' debug3: key_read: missing keytype debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug2: key_type_from_name: unknown key type '-----END' debug3: key_read: missing keytype debug1: identity file /Users/Broc/.ssh/EC2Keypair.pem type -1 debug3: Not a RSA1 key file /Users/Broc/.ssh/id_rsa. debug2: key_type_from_name: unknown key type '-----BEGIN' debug3: key_read: missing keytype debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug3: key_read: missing whitespace debug2: key_type_from_name: unknown key type '-----END' debug3: key_read: missing keytype debug1: identity file /Users/Broc/.ssh/id_rsa type 1 debug1: Remote protocol version 2.0, remote software version OpenSSH_5.1p1 Debian-6ubuntu2 debug1: match: OpenSSH_5.1p1 Debian-6ubuntu2 pat OpenSSH* debug1: Enabling compatibility mode for protocol 2.0 debug1: Local version string SSH-2.0-OpenSSH_5.2 debug2: fd 3 setting O_NONBLOCK debug1: SSH2_MSG_KEXINIT sent debug1: SSH2_MSG_KEXINIT received debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1 debug2: kex_parse_kexinit: ssh-rsa,ssh-dss debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected] debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected] debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96 debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96 debug2: kex_parse_kexinit: none,[email protected],zlib debug2: kex_parse_kexinit: none,[email protected],zlib debug2: kex_parse_kexinit: debug2: kex_parse_kexinit: debug2: kex_parse_kexinit: first_kex_follows 0 debug2: kex_parse_kexinit: reserved 0 debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1 debug2: kex_parse_kexinit: ssh-rsa,ssh-dss debug2: kex_parse_kexinit: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,arcfour256,arcfour,aes192-cbc,aes256-cbc,[email protected],aes128-ctr,aes192-ctr,aes256-ctr debug2: kex_parse_kexinit: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,arcfour256,arcfour,aes192-cbc,aes256-cbc,[email protected],aes128-ctr,aes192-ctr,aes256-ctr debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96 debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96 debug2: kex_parse_kexinit: none,[email protected] debug2: kex_parse_kexinit: none,[email protected] debug2: kex_parse_kexinit: debug2: kex_parse_kexinit: debug2: kex_parse_kexinit: first_kex_follows 0 debug2: kex_parse_kexinit: reserved 0 debug2: mac_setup: found hmac-md5 debug1: kex: server->client aes128-ctr hmac-md5 none debug2: mac_setup: found hmac-md5 debug1: kex: client->server aes128-ctr hmac-md5 none debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP debug2: dh_gen_key: priv key bits set: 123/256 debug2: bits set: 500/1024 debug1: SSH2_MSG_KEX_DH_GEX_INIT sent debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY debug3: check_host_in_hostfile: filename /Users/Broc/.ssh/known_hosts debug3: check_host_in_hostfile: match line 106 debug3: check_host_in_hostfile: filename /Users/Broc/.ssh/known_hosts debug3: check_host_in_hostfile: match line 106 debug1: Host 'ec2-xxx.compute-1.amazonaws.com' is known and matches the RSA host key. debug1: Found key in /Users/Broc/.ssh/known_hosts:106 debug2: bits set: 521/1024 debug1: ssh_rsa_verify: signature correct debug2: kex_derive_keys debug2: set_newkeys: mode 1 debug1: SSH2_MSG_NEWKEYS sent debug1: expecting SSH2_MSG_NEWKEYS debug2: set_newkeys: mode 0 debug1: SSH2_MSG_NEWKEYS received debug1: SSH2_MSG_SERVICE_REQUEST sent debug2: service_accept: ssh-userauth debug1: SSH2_MSG_SERVICE_ACCEPT received debug2: key: /Users/Broc/.ssh/id_rsa (0x100125f70) debug2: key: /Users/Broc/.ssh/EC2Keypair.pem (0x0) debug1: Authentications that can continue: publickey debug3: start over, passed a different list publickey debug3: preferred publickey,keyboard-interactive,password debug3: authmethod_lookup publickey debug3: remaining preferred: keyboard-interactive,password debug3: authmethod_is_enabled publickey debug1: Next authentication method: publickey debug1: Offering public key: /Users/Broc/.ssh/id_rsa debug3: send_pubkey_test debug2: we sent a publickey packet, wait for reply debug1: Authentications that can continue: publickey debug1: Trying private key: /Users/Broc/.ssh/EC2Keypair.pem debug1: read PEM private key done: type RSA debug3: sign_and_send_pubkey debug2: we sent a publickey packet, wait for reply debug1: Authentications that can continue: publickey debug2: we did not send a packet, disable method debug1: No more authentication methods to try. Permission denied (publickey). [Broc-MBP.local]: Broc:~/.ssh ? So, right now I'm really at a loss and not sure what to do. While I've already got another system taking the place of this one I'd really like to have access back :|

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• hyperv vss writer unexpected error

  - by Eric Martin

  I am using Mozy Pro to backup our Hyperv servers. I am doing this without any issues on a 2nd server but this box hasn't backed up sucessfully yet. I was told by the support tech at Mozy to type: vssadmin list providers >c:\providers.txt vssadmin list writers >c:\writers.txt Writers.txt: vssadmin 1.1 - Volume Shadow Copy Service administrative command-line tool (C) Copyright 2001-2013 Microsoft Corp. Writer name: 'Task Scheduler Writer' Writer Id: {d61d61c8-d73a-4eee-8cdd-f6f9786b7124} Writer Instance Id: {1bddd48e-5052-49db-9b07-b96f96727e6b} State: [1] Stable Last error: No error Writer name: 'VSS Metadata Store Writer' Writer Id: {75dfb225-e2e4-4d39-9ac9-ffaff65ddf06} Writer Instance Id: {088e7a7d-09a8-4cc6-a609-ad90e75ddc93} State: [1] Stable Last error: No error Writer name: 'Performance Counters Writer' Writer Id: {0bada1de-01a9-4625-8278-69e735f39dd2} Writer Instance Id: {f0086dda-9efc-47c5-8eb6-a944c3d09381} State: [1] Stable Last error: No error Writer name: 'System Writer' Writer Id: {e8132975-6f93-4464-a53e-1050253ae220} Writer Instance Id: {506e7d9c-ded3-4edf-824a-4dd9af7f7538} State: [1] Stable Last error: No error Writer name: 'ASR Writer' Writer Id: {be000cbe-11fe-4426-9c58-531aa6355fc4} Writer Instance Id: {1de438e4-09de-487c-9ea8-eeafbe3fd210} State: [1] Stable Last error: No error Writer name: 'COM+ REGDB Writer' Writer Id: {542da469-d3e1-473c-9f4f-7847f01fc64f} Writer Instance Id: {511d23d9-4cbb-400f-b739-e6e0a8ecdbee} State: [1] Stable Last error: No error Writer name: 'Microsoft Hyper-V VSS Writer' Writer Id: {66841cd4-6ded-4f4b-8f17-fd23f8ddc3de} Writer Instance Id: {32f41185-2b20-41ff-a7aa-92c262f578cd} State: [1] Stable Last error: Unexpected error Writer name: 'Registry Writer' Writer Id: {afbab4a2-367d-4d15-a586-71dbb18f8485} Writer Instance Id: {fa328ece-623f-43cc-9888-e897e108c40e} State: [1] Stable Last error: No error Writer name: 'Shadow Copy Optimization Writer' Writer Id: {4dc3bdd4-ab48-4d07-adb0-3bee2926fd7f} Writer Instance Id: {7b582861-7f7f-4c10-adb1-5106bcab3902} State: [1] Stable Last error: No error Writer name: 'WMI Writer' Writer Id: {a6ad56c2-b509-4e6c-bb19-49d8f43532f0} Writer Instance Id: {d2f73a0f-c19a-44cc-bcd2-6c84ac6e516b} State: [1] Stable Last error: No error Writer name: 'MSMQ Writer (MSMQ)' Writer Id: {7e47b561-971a-46e6-96b9-696eeaa53b2a} Writer Instance Id: {95ea6efc-c00c-47ca-90d1-28fbe6d7a8d0} State: [1] Stable Last error: No error Writer name: 'IIS Config Writer' Writer Id: {2a40fd15-dfca-4aa8-a654-1f8c654603f6} Writer Instance Id: {d5a32f43-0675-400d-8502-cdece4c867e1} State: [1] Stable Last error: No error Providers.txt: vssadmin 1.1 - Volume Shadow Copy Service administrative command-line tool (C) Copyright 2001-2013 Microsoft Corp. Provider name: 'Microsoft File Share Shadow Copy provider' Provider type: Fileshare Provider Id: {89300202-3cec-4981-9171-19f59559e0f2} Version: 1.0.0.1 Provider name: 'Microsoft Software Shadow Copy provider 1.0' Provider type: System Provider Id: {b5946137-7b9f-4925-af80-51abd60b20d5} Version: 1.0.0.7 The tech said I needed to resolve this issue: Writer name: 'Microsoft Hyper-V VSS Writer' Writer Id: {66841cd4-6ded-4f4b-8f17-fd23f8ddc3de} Writer Instance Id: {32f41185-2b20-41ff-a7aa-92c262f578cd} State: [1] Stable Last error: Unexpected error I checked the event viewer and this is the only thing I found related to hyperv: I don't know where to start to resolve this or to find out where the issue is at. I know nothing of the vss writer for hyperv so any input would be greatly appreciated.

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• How to update the filename of a Django's FileField instance ?

  - by pierre-guillaume-degans

  Hello, Here a simple django model: class SomeModel(models.Model): title = models.CharField(max_length=100) video = models.FileField(upload_to='video') I would like to save any instance so that the video's file name would be a valid file name of the title. For example, in the admin interface, I load a new instance with title "Lorem ipsum" and a video called "video.avi". The copy of the file on the server should be "Lorem Ipsum.avi" (or "Lorem_Ipsum.avi"). Thank you :)

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• How can I know whether an instance implements a method in Objective-C ?

  - by Thomas Joulin

  I would like to know if an instance implements a specific method. I could use respondsToSelector: but it returns YES if the instance inherits the method... I could loop through the methods of class_copyMethodList(), but since I might want to check a lot of instances, I wanted to know if there was a simpler solution (like repondsToSelector:, but restricted to the class itself...)

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• Can I do a URL Rewrite to a different Tomcat instance?

  - by RodeoClown

  Is is possible to use Tuckey's URL Rewrite to rewrite to a different Tomcat instance? I have it working using crossContext="true" rewriting to a different servlet on the same tomcat instance, but our production server has multiple tomcat instances running and I want to rewrite to one of them instead? If it's not possible using the URL Rewrite filter, is there another way of doing it? Thanks.

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• .NET Reflection: How to call method of interface without creating instance?

  - by jitm

  I have situation where I have to call method of interface using reflection, like this object x = null; MethodInfo method = interfaceExists.GetMethod("ShutDown"); method.Invoke(x, new object[] { 4 }) As you can see I do not create instance of object! And, as I can supposed, I receive exception Non-static method requires a target And Question, Can I call method of interface using reflection without creating instance of interface and if YES, How I can do it ?

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• How do I handle the Maybe result of at in Control.Lens.Indexed without a Monoid instance

  - by Matthias Hörmann

  I recently discovered the lens package on Hackage and have been trying to make use of it now in a small test project that might turn into a MUD/MUSH server one very distant day if I keep working on it. Here is a minimized version of my code illustrating the problem I am facing right now with the at lenses used to access Key/Value containers (Data.Map.Strict in my case) {-# LANGUAGE OverloadedStrings, GeneralizedNewtypeDeriving, TemplateHaskell #-} module World where import Control.Applicative ((<$>),(<*>), pure) import Control.Lens import Data.Map.Strict (Map) import qualified Data.Map.Strict as DM import Data.Maybe import Data.UUID import Data.Text (Text) import qualified Data.Text as T import System.Random (Random, randomIO) newtype RoomId = RoomId UUID deriving (Eq, Ord, Show, Read, Random) newtype PlayerId = PlayerId UUID deriving (Eq, Ord, Show, Read, Random) data Room = Room { _roomId :: RoomId , _roomName :: Text , _roomDescription :: Text , _roomPlayers :: [PlayerId] } deriving (Eq, Ord, Show, Read) makeLenses ''Room data Player = Player { _playerId :: PlayerId , _playerDisplayName :: Text , _playerLocation :: RoomId } deriving (Eq, Ord, Show, Read) makeLenses ''Player data World = World { _worldRooms :: Map RoomId Room , _worldPlayers :: Map PlayerId Player } deriving (Eq, Ord, Show, Read) makeLenses ''World mkWorld :: IO World mkWorld = do r1 <- Room <$> randomIO <*> (pure "The Singularity") <*> (pure "You are standing in the only place in the whole world") <*> (pure []) p1 <- Player <$> randomIO <*> (pure "testplayer1") <*> (pure $ r1^.roomId) let rooms = at (r1^.roomId) ?~ (set roomPlayers [p1^.playerId] r1) $ DM.empty players = at (p1^.playerId) ?~ p1 $ DM.empty in do return $ World rooms players viewPlayerLocation :: World -> PlayerId -> RoomId viewPlayerLocation world playerId= view (worldPlayers.at playerId.traverse.playerLocation) world Since rooms, players and similar objects are referenced all over the code I store them in my World state type as maps of Ids (newtyped UUIDs) to their data objects. To retrieve those with lenses I need to handle the Maybe returned by the at lens (in case the key is not in the map this is Nothing) somehow. In my last line I tried to do this via traverse which does typecheck as long as the final result is an instance of Monoid but this is not generally the case. Right here it is not because playerLocation returns a RoomId which has no Monoid instance. No instance for (Data.Monoid.Monoid RoomId) arising from a use of `traverse' Possible fix: add an instance declaration for (Data.Monoid.Monoid RoomId) In the first argument of `(.)', namely `traverse' In the second argument of `(.)', namely `traverse . playerLocation' In the second argument of `(.)', namely `at playerId . traverse . playerLocation' Since the Monoid is required by traverse only because traverse generalizes to containers of sizes greater than one I was now wondering if there is a better way to handle this that does not require semantically nonsensical Monoid instances on all types possibly contained in one my objects I want to store in the map. Or maybe I misunderstood the issue here completely and I need to use a completely different bit of the rather large lens package?

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• How to detect if collection contain instance of specific type?

  - by KentZhou

  Suppose I create collection like Collection<IMyType> coll; Then I have many implelentations of IMyTypem like, T1, T2, T3... Then I want know if the collection coll contains a instance of type T1. So I want to write a method like public bool ContainType( <T>){...} here the param should be class type, not class instance. How to write code for this kind of issue?

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• how to determine date when service pack was applied to SQL Server instance?

  - by Oliver

  For an instance of SQL Server 2005/2008, how can one determine the date and time when a service pack was applied to the instance? Is there a system table or view that stores that information?

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• What is the correct way to create a single instance application?

  - by Nidonocu

  Using C# and WPF under .net (rather than WindowsForms or console), what is the correct way to create an application that can only be run as a single instance? I know it has something to do with some mythical thing called a mutex, rarely can I find someone that bothers to stop and explain what one of these are. The code needs to also inform the already running instance that the user tried to start a second one, and maybe also pass any command line arguments if any existed.

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• In Ruby on Rails, how is view code able to use instance variables that are set inside the controller

  - by Jian Lin

  In Ruby on Rails, how is an ActionView object able to access the instance variables of ActionController object (how is view code able to use instance variables that are set inside the controller code)?

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• Is it a good or bad practice to call instance methods from a java constructor?

  - by Steve

  There are several different ways I can initialize complex objects (with injected dependencies and required set-up of injected members), are all seem reasonable, but have various advantages and disadvantages. I'll give a concrete example: final class MyClass { private final Dependency dependency; @Inject public MyClass(Dependency dependency) { this.dependency = dependency; dependency.addHandler(new Handler() { @Override void handle(int foo) { MyClass.this.doSomething(foo); } }); doSomething(0); } private void doSomething(int foo) { dependency.doSomethingElse(foo+1); } } As you can see, the constructor does 3 things, including calling an instance method. I've been told that calling instance methods from a constructor is unsafe because it circumvents the compiler's checks for uninitialized members. I.e. I could have called doSomething(0) before setting this.dependency, which would have compiled but not worked. What is the best way to refactor this? Make doSomething static and pass in the dependency explicitly? In my actual case I have three instance methods and three member fields that all depend on one another, so this seems like a lot of extra boilerplate to make all three of these static. Move the addHandler and doSomething into an @Inject public void init() method. While use with Guice will be transparent, it requires any manual construction to be sure to call init() or else the object won't be fully-functional if someone forgets. Also, this exposes more of the API, both of which seem like bad ideas. Wrap a nested class to keep the dependency to make sure it behaves properly without exposing additional API:class DependencyManager { private final Dependency dependency; public DependecyManager(Dependency dependency) { ... } public doSomething(int foo) { ... } } @Inject public MyClass(Dependency dependency) { DependencyManager manager = new DependencyManager(dependency); manager.doSomething(0); } This pulls instance methods out of all constructors, but generates an extra layer of classes, and when I already had inner and anonymous classes (e.g. that handler) it can become confusing - when I tried this I was told to move the DependencyManager to a separate file, which is also distasteful because it's now multiple files to do a single thing. So what is the preferred way to deal with this sort of situation?

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• If I have a Riak DB, should it store to Amazon S3 or to the EC/2 instance?

  - by tesmar

  I am setting up an Amazon EC/2 instance, and am putting Riak on it. I am wondering if I should store the data locally (and not ever delete the instance), or set up Riak to store to S3 and bring up/take down instances as I need?

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• What is the easiest, most concise way to make selected attributes in an instance be readonly?

  - by Kevin Little

  In Python, I want to make selected instance attributes of a class be readonly to code outside of the class. I want there to be no way outside code can alter the attribute, except indirectly by invoking methods on the instance. I want the syntax to be concise. What is the best way? (I give my current best answer below...)

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• Would the instance reference parameters passed into the static methods get garbage collected?

  - by 123Developer

  I know that the static objects in .Net managed world are loaded in Loader Heap which is never going to be garbage collected. What happens to the instance reference parameters passed to a static methods. Are they get garbage collected once the static function executed completely Or they are going to live forever as those instance reference variables are once passed to static method? I am really confused this evening; Please guide me. Thanks and regards 123Developer.

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• C# Reflection: How to call method of interface without creating instance?

  - by jitm

  Hello, I have situation where I have to call method of interface using reflection, like this object x = null; MethodInfo method = interfaceExists.GetMethod("ShutDown"); method.Invoke(x, new object[] { 4 }) As you can see I do not create instance of object! And, as I can supposed, I receive exception Non-static method requires a target And Question, Can I call method of interface using reflection without creating instance of interface and if YES, How I can do it ? Thank you.

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• How to see if type is instance of a class in Haskell?

  - by Raekye

  I'm probably doing this completely wrong (the unhaskell way); I'm just learning so please let me know if there's a better way to approach this. Context: I'm writing a bunch of tree structures. I want to reuse my prettyprint function for binary trees. Not all trees can use the generic Node/Branch data type though; different trees need different extra data. So to reuse the prettyprint function I thought of creating a class different trees would be instances of: class GenericBinaryTree a where is_leaf :: a -> Bool left :: a -> a node :: a -> b right :: a -> a This way they only have to implement methods to retrieve the left, right, and current node value, and prettyprint doesn't need to know about the internal structure. Then I get down to here: prettyprint_helper :: GenericBinaryTree a => a -> [String] prettyprint_helper tree | is_leaf tree = [] | otherwise = ("{" ++ (show (node tree)) ++ "}") : (prettyprint_subtree (left tree) (right tree)) where prettyprint_subtree left right = ((pad "+- " "| ") (prettyprint_helper right)) ++ ((pad "`- " " ") (prettyprint_helper left)) pad first rest = zipWith (++) (first : repeat rest) And I get the Ambiguous type variable 'a0' in the constraint: (Show a0) arising from a use of 'show' error for (show (node tree)) Here's an example of the most basic tree data type and instance definition (my other trees have other fields but they're irrelevant to the generic prettyprint function) data Tree a = Branch (Tree a) a (Tree a) | Leaf instance GenericBinaryTree (Tree a) where is_leaf Leaf = True is_leaf _ = False left (Branch left node right) = left right (Branch left node right) = right node (Branch left node right) = node I could have defined node :: a -> [String] and deal with the stringification in each instance/type of tree, but this feels neater. In terms of prettyprint, I only need a string representation, but if I add other generic binary tree functions later I may want the actual values. So how can I write this to work whether the node value is an instance of Show or not? Or what other way should I be approaching this problem? In an object oriented language I could easily check whether a class implements something, or if an object has a method. I can't use something like prettyprint :: Show a => a -> String Because it's not the tree that needs to be showable, it's the value inside the tree (returned by function node) that needs to be showable. I also tried changing node to Show b => a -> b without luck (and a bunch of other type class/preconditions/whatever/I don't even know what I'm doing anymore).

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• How to upload stuff to Amazon EC2 Windows instance?

  - by JohnIdol

  I've never used Amazon EC2 - I am thinking to test a few instances for running intensive computation processes I have a requirement for rather than buying real hardware. I am given to understand the thing is quite easy to setup - but I have no clue of how it actually works, in terms of transferring data to my ec2 instances. So the question is how can I upload stuff to my instance? Any help appreciated!

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• creating EBS volumn from and attaching to the same instance ?

  - by system-matrix

  Is it possible to create a EBS volume from and attach it to the same instance? will boto be of some help?

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• Which config file gets changed in an embedded tomcat instance to enable gzip compression?

  - by spowers

  Our developers have provided a web application bundled with an 'embedded' instance of tomcat. They have not enabled gzip compression of css or js files, and am wondering if there is a standard configuration file to change this in like there is with a standalone tomcat server?

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• Is Xen virtualization similar with amazon's S3 creating an instance?

  - by grokker

  Hi is Xen virtualization similar with Amazon's S3 creating an instance? What's the difference between then and what about cloud computing? Thanks in advance!

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• What acronym do you often hear used incorrectly? For instance HTTP protocol?

  - by Stewart Robinson

  What acronym do you often hear used incorrectly? For instance ATM Machine, or DNS Server. So annoying! Edit: There is nothing wrong with DNS Server as the S in DNS is System. Instead how about UDP Protocol?

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• Amazon EC2 - Are multiple requests from the same user guaranteed to go to the same instance?

  - by hamlin11

  In a scenario where an application is hosted by multiple instances in Amazon EC2 (with load balancing), are multiple requests from the same user guaranteed to go to the same instance?

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• Why is my concurrency capacity so low for my web app on a LAMP EC2 instance?

  - by AMF

  I come from a web developer background and have been humming along building my PHP app, using the CakePHP framework. The problem arose when I began the ab (Apache Bench) testing on the Amazon EC2 instance in which the app resides. I'm getting pretty horrendous average page load times, even though I'm running a c1.medium instance (2 cores, 2GB RAM), and I think I'm doing everything right. I would run: ab -n 200 -c 20 http://localhost/heavy-but-view-cached-page.php Here are the results: Concurrency Level: 20 Time taken for tests: 48.197 seconds Complete requests: 200 Failed requests: 0 Write errors: 0 Total transferred: 392111200 bytes HTML transferred: 392047600 bytes Requests per second: 4.15 [#/sec] (mean) Time per request: 4819.723 [ms] (mean) Time per request: 240.986 [ms] (mean, across all concurrent requests) Transfer rate: 7944.88 [Kbytes/sec] received While the ab test is running, I run VMStat, which shows that Swap stays at 0, CPU is constantly at 80-100% (although I'm not sure I can trust this on a VM), RAM utilization ramps up to about 1.6G (leaving 400M free). Load goes up to about 8 and site slows to a crawl. Here's what I think I'm doing right on the code side: In Chrome browser uncached pages typically load in 800-1000ms, and cached pages load in 300-500ms. Not stunning, but not terrible either. Thanks to view caching, there might be at most one DB query per page-load to write session data. So we can rule out a DB bottleneck. I have APC on. I am using Memcached to serve the view cache and other site caches. xhprof code profiler shows that cached pages take up 10MB-40MB in memory and 100ms - 1000ms in wall time. Pages that would be the worst offenders would look something like this in xhprof: Total Incl. Wall Time (microsec): 330,143 microsecs Total Incl. CPU (microsecs): 320,019 microsecs Total Incl. MemUse (bytes): 36,786,192 bytes Total Incl. PeakMemUse (bytes): 46,667,008 bytes Number of Function Calls: 5,195 My Apache config: KeepAlive On MaxKeepAliveRequests 100 KeepAliveTimeout 3 <IfModule mpm_prefork_module> StartServers 5 MinSpareServers 5 MaxSpareServers 10 MaxClients 120 MaxRequestsPerChild 1000 </IfModule> Is there something wrong with the server? Some gotcha with the EC2? Or is it my code? Some obvious setting I should look into? Too many DNS lookups? What am I missing? I really want to get to 1,000 concurrency capacity, but at this rate, it ain't gonna happen.

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• Is it possible to create a second instance on SQL Server 2005 on same system ?

  - by Tiberiu Hajas

  I would like to know if it's possible to create another instance of SQLServer 2005, to have 2 instances running on the same system ? thanks

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