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  • Aggregation over a few models - Django

    - by RadiantHex
    Hi folks, I'm trying to compute the average of a field over various subsets of a queryset. Player.objects.order_by('-score').filter(sex='male').aggregate(Avg('level')) This works perfectly! But... if I try to compute it for the top 50 players it does not work. Player.objects.order_by('-score').filter(sex='male')[:50].aggregate(Avg('level')) This last one returns the exact same result as the query above it, which is wrong. What am I doing wrong? Help would be very much appreciated!

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  • Vagrant (Virtualbox) host-only multiple node networking issue

    - by Lorin Hochstein
    I'm trying to use a multi-VM vagrant environment as a testbed for deploying OpenStack, and I've run into a networking problem with trying to communicate from one VM, to a VM-inside-of-a-VM. I have two Vagrant nodes, a cloud controller node and a compute node. I'm using host-only networking. My Vagrantfile looks like this: Vagrant::Config.run do |config| config.vm.box = "precise64" config.vm.define :controller do |controller_config| controller_config.vm.network :hostonly, "192.168.206.130" # eth1 controller_config.vm.network :hostonly, "192.168.100.130" # eth2 controller_config.vm.host_name = "controller" end config.vm.define :compute1 do |compute1_config| compute1_config.vm.network :hostonly, "192.168.206.131" # eth1 compute1_config.vm.network :hostonly, "192.168.100.131" # eth2 compute1_config.vm.host_name = "compute1" compute1_config.vm.customize ["modifyvm", :id, "--memory", 1024] end end When I try to start up a (QEMU-based) VM, it boots successfully on compute1, and its virtual nic (vnet0) is connected via a bridge, br100: root@compute1:~# brctl show 100 bridge name bridge id STP enabled interfaces br100 8000.08002798c6ef no eth2 vnet0 When the QEMU VM makes a request to the DHCP server (dnsmasq) running on controller, I can see the request reaches the controller because of the output on the syslog on the controller: Aug 6 02:34:56 precise64 dnsmasq-dhcp[12042]: DHCPDISCOVER(br100) fa:16:3e:07:98:11 Aug 6 02:34:56 precise64 dnsmasq-dhcp[12042]: DHCPOFFER(br100) 192.168.100.2 fa:16:3e:07:98:11 However, the DHCPOFFER never makes it back to the VM running on compute1. If I watch the requests using tcpdump on the vboxnet3 interface on my host machine that runs Vagrant (Mac OS X), I can see both the requests and the replies $ sudo tcpdump -i vboxnet3 -n port 67 or port 68 tcpdump: WARNING: vboxnet3: That device doesn't support promiscuous mode (BIOCPROMISC: Operation not supported on socket) tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on vboxnet3, link-type EN10MB (Ethernet), capture size 65535 bytes 22:51:20.694040 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from fa:16:3e:07:98:11, length 280 22:51:20.694057 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from fa:16:3e:07:98:11, length 280 22:51:20.696047 IP 192.168.100.1.67 > 192.168.100.2.68: BOOTP/DHCP, Reply, length 311 22:51:23.700845 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from fa:16:3e:07:98:11, length 280 22:51:23.700876 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from fa:16:3e:07:98:11, length 280 22:51:23.701591 IP 192.168.100.1.67 > 192.168.100.2.68: BOOTP/DHCP, Reply, length 311 22:51:26.705978 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from fa:16:3e:07:98:11, length 280 22:51:26.705995 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from fa:16:3e:07:98:11, length 280 22:51:26.706527 IP 192.168.100.1.67 > 192.168.100.2.68: BOOTP/DHCP, Reply, length 311 But, if I tcpdump on eth2 on compute, I only see the requests, not the replies: root@compute1:~# tcpdump -i eth2 -n port 67 or port 68 tcpdump: WARNING: eth2: no IPv4 address assigned tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes 02:51:20.240672 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from fa:16:3e:07:98:11, length 280 02:51:23.249758 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from fa:16:3e:07:98:11, length 280 02:51:26.258281 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from fa:16:3e:07:98:11, length 280 At this point, I'm stuck. I'm not sure why the DHCP replies aren't making it to the compute node. Perhaps it has something to do with the configuration of the VirtualBox virtual switch/router? Note that eth2 interfaces on both nodes have been set to promiscuous mode.

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  • http request via iptables --to-destination ip redirect results in no response

    - by Wouter Vegter
    I have two Ubuntu servers with each having their own ip addresses. Let's call them server1 and server2, having respectively ip 1.1.1.1 and 2.2.2.2 I have a nginx running on server2. The sole purpose I want server1 to have is to redirect all incoming http (so port 80) requests to server2 without clients noticing that their request is being redirected. I tried the following command on server1: iptables -t nat -A PREROUTING -p tcp --dport 80 -j DNAT --to-destination 2.2.2.2 But when I enter 1.1.1.1 in my browser I get no respond: the page keeps trying to load without giving any message or error message (I get a time-out after 2-3 mins). But when I do remove the above iptables rule I immediately do get a "page not found error" when I enter 1.1.1.1 in my browser; so something is working but not as it should: when I enter 1.1.1.1 I want the html page to load that is hosted on 2.2.2.2 Because when i enter 2.2.2.2 in my browser I do see the webpage loaded. Could anyone please help me with this? I am searching quite some time (on severfault & Google) on this now so that's why I ask. Many thanks for reading my question! Update: Thank you all for you information. Unfortunately I still get no response I have the following iptables configuration: root@ip-10-48-238-216:/home/ubuntu# sudo iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination root@ip-10-48-238-216:/home/ubuntu# sudo iptables -t nat -L Chain PREROUTING (policy ACCEPT) target prot opt source destination DNAT tcp -- anywhere anywhere tcp dpt:www to:2.2.2.2 Chain OUTPUT (policy ACCEPT) target prot opt source destination Chain POSTROUTING (policy ACCEPT) target prot opt source destination When i run tcpdump and do request via chrome to 1.1.1.1 i get the following root@ip-10-48-238-216:/home/ubuntu# sudo tcpdump -i eth0 port 80 -vv tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes 13:56:18.346625 IP (tos 0x0, ttl 52, id 12055, offset 0, flags [DF], proto TCP (6), length 60) 212-123-161-112.ip.telfort.nl.16386 ip-10-48-238-216.eu-west-1.compute.internal.www: Flags [S], cksum 0xb398 (correct), seq 2639758575, win 5840, options [mss 1460,sackOK,TS val 1223672 ecr 0,nop,wscale 6], length 0 13:56:18.346662 IP (tos 0x0, ttl 51, id 12055, offset 0, flags [DF], proto TCP (6), length 60) 212-123-161-112.ip.telfort.nl.16386 ww1dc1.shopreme.com.www: Flags [S], cksum 0x9ee0 (correct), seq 2639758575, win 5840, options [mss 1460,sackOK,TS val 1223672 ecr 0,nop,wscale 6], length 0 13:56:18.598747 IP (tos 0x0, ttl 52, id 10138, offset 0, flags [DF], proto TCP (6), length 60) 212-123-161-112.ip.telfort.nl.16387 ip-10-48-238-216.eu-west-1.compute.internal.www: Flags [S], cksum 0xac40 (correct), seq 2645658541, win 5840, options [mss 1460,sackOK,TS val 1223735 ecr 0,nop,wscale 6], length 0 13:56:18.598777 IP (tos 0x0, ttl 51, id 10138, offset 0, flags [DF], proto TCP (6), length 60) 212-123-161-112.ip.telfort.nl.16387 ww1dc1.shopreme.com.www: Flags [S], cksum 0x9788 (correct), seq 2645658541, win 5840, options [mss 1460,sackOK,TS val 1223735 ecr 0,nop,wscale 6], length 0 ^C 4 packets captured 4 packets received by filter 0 packets dropped by kernel the mentioned address relate to the following 212-123-161-112.ip.telfort.nl.16386 : my personal computer ww1dc1.shopreme.com.www : dns of server2 (2.2.2.2) ip-10-48-238-216.eu-west-1.compute.internal.www : amazon web services ec2 internal address of server1 (1.1.1.1) However, the tcpdump log on server2 (2.2.2.2) stays empty and I get no response back in my browser. I am able to ping from server1 to server2. And net.ipv4.ip_forward is set to 1 and so is /proc/sys/net/ipv4/ip_forward Could there be anything else that is missing?

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  • Varnish VCL - Regular Expression Evaluation

    - by Hugues ALARY
    I have been struggling for the past few days with this problem: Basically, I want to send to a client browser a cookie of the form foo[sha1oftheurl]=[randomvalue] if and only if the cookie has not already been set. e.g. If a client browser requests "/page.html", the HTTP response will be like: resp.http.Set-Cookie = "foo4c9ae249e9e061dd6e30893e03dc10a58cc40ee6=ABCD;" then, if the same client request "/index.html", the HTTP response will contain a header: resp.http.Set-Cookie = "foo14fe4559026d4c5b5eb530ee70300c52d99e70d7=QWERTY;" In the end, the client browser will have 2 cookies: foo4c9ae249e9e061dd6e30893e03dc10a58cc40ee6=ABCD foo14fe4559026d4c5b5eb530ee70300c52d99e70d7=QWERTY Now, that, is not complicated in itself. The following code does it: import digest; import random; ##This vmod does not exist, it's just for the example. sub vcl_recv() { ## We compute the sha1 of the requested URL and store it in req.http.Url-Sha1 set req.http.Url-Sha1 = digest.hash_sha1(req.url); set req.http.random-value = random.get_rand(); } sub vcl_deliver() { ## We create a cookie on the client browser by creating a "Set-Cookie" header ## In our case the cookie we create is of the form foo[sha1]=[randomvalue] ## e.g for a URL "/page.html" the cookie will be foo4c9ae249e9e061dd6e30893e03dc10a58cc40ee6=[randomvalue] set resp.http.Set-Cookie = {""} + resp.http.Set-Cookie + "foo"+req.http.Url-Sha1+"="+req.http.random-value; } However, this code does not take into account the case where the Cookie already exists. I need to check that the Cookie does not exists before generating a random value. So I thought about this code: import digest; import random; sub vcl_recv() { ## We compute the sha1 of the requested URL and store it in req.http.Url-Sha1 set req.http.Url-Sha1 = digest.hash_sha1(req.url); set req.http.random-value = random.get_rand(); set req.http.regex = "abtest"+req.http.Url-Sha1; if(!req.http.Cookie ~ req.http.regex) { set req.http.random-value = random.get_rand(); } } The problem is that Varnish does not compute Regular expression at run time. Which leads to this error when I try to compile: Message from VCC-compiler: Expected CSTR got 'req.http.regex' (program line 940), at ('input' Line 42 Pos 31) if(req.http.Cookie !~ req.http.regex) { ------------------------------##############--- Running VCC-compiler failed, exit 1 VCL compilation failed One could propose to solve my problem by matching on the "abtest" part of the cookie or even "abtest[a-fA-F0-9]{40}": if(!req.http.Cookie ~ "abtest[a-fA-F0-9]{40}") { set req.http.random-value = random.get_rand(); } But this code matches any cookie starting by 'abtest' and containing an hexadecimal string of 40 characters. Which means that if a client requests "/page.html" first, then "/index.html", the condition will evaluate to true even if the cookie for the "/index.html" has not been set. I found in bug report phk or someone else stating that computing regular expressions was extremely expensive which is why they are evaluated during compilation. Considering this, I believe that there is no way of achieving what I want the way I've been trying to. Is there any way of solving this problem, other than writting a vmod? Thanks for your help! -Hugues

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  • Christian Beauclair on Azure

    - by guybarrette
    Microsoft Canada’s Christian Beauclair was interviewed for an IT in Canada article where he describes these Cloud patterns: Transparency Scale in multi tenancy Burst compute Elastic storage Read it here var addthis_pub="guybarrette";

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  • Christian Beauclair on Azure

    Microsoft Canadas Christian Beauclair was interviewed for an IT in Canada article where he describes these Cloud patterns: Transparency Scale in multi tenancy Burst compute Elastic storage Read it here var addthis_pub="guybarrette";...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Google intègre CoreOS à sa plateforme cloud, « un hôte idéal pour les systèmes distribués » estime Brandon Philips

    Google intègre CoreOS à sa plateforme cloud, « un hôte idéal pour les systèmes distribués » estime Brandon Philips Google rallonge la liste des distributions Linux pouvant être prises en charge par Google Compute Engine. Ainsi, CoreOS, qui était déjà disponible en preview depuis décembre dernier, fait désormais part entière des offres de la plateforme au même titre que Debian, RedHat ou encore Suse. Les entreprises pourront la tester et l'utiliser facilement pour leurs clusters et leurs applications...

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  • Ranking Part III

    - by PointsToShare
    © 2011 By: Dov Trietsch. All rights reserved   Ranking Part III In a previous blogs “Ranking an Introduction” and  “Ranking Part II” , you have already praised me in “Rank the Author” and learned how to create a new element on a page and how to place it where you need it. For this installment, I just added code to keep the number of votes (you vote by clicking one of the stars) and the total vote. Using these two, we can compute the average rating. It’s a small step, but its purpose is to show that we do not need a detailed history in order to compute the average. A running total is sufficient. Please note that once you close the game, you will lose your previous total. In real life, we persist the totals in the list itself. We also keep a list of actual votes, but its purpose is to prevent double votes. If a person has already voted, his user id is already on the list and our program will check for it and bar the person from voting again. This is coded in an event receiver, which is a SharePoint server piece of code. I will show you how to do this part in a subsequent blog. Again, go to the page and look at the code. The gist of it is here. avg, votes, and stars are global variables that I defined before. function sendRate(sel){//I hate long line so I created pieces of the message in their own vars            var s1 = "Your Rating Was: ";            var s2 = ".. ";            var s3 = "\nVotes = ";            var s4 = "\nTotal Stars = ";            var s5 = "\nAverage = ";            var s;            s = parseInt(sel.id.replace("_", '')); // Get the selected star number            votes = parseInt(votes) + 1;            stars = parseInt(stars) + s;            avg = parseFloat(stars) / parseFloat(votes);            alert(s1 + sel.id + s2 +sel.title + s3 + votes + s4 + stars + s5 + avg);} Click on the link to play and examine “Ranking with Stats” That’s all folks!

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  • Is it possible to billboard a sprite using a transformation matrix?

    - by Ross
    None of the current topics on billboarding seemed to answer this question. But, given a sprite (or quad) that has it's own 4x4 transformation matrix a camera with a view matrix (a standard 4x4 transformation matrix) is it possible to compute a 4x4 transformation matrix such that when the quad's matrix is multiplied with this matrix it has an orientation of looking at the camera? Thank you in advance.

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  • PASS 13 Dispatches: moving to the cloud

    - by Tony Davis
    PASS Summit 13, Day 1 keynote by Quentin Clarke and we're hearing about “redefiniing mission critical in the cloud”. With a move to the Windows Azure cloud comes the promise of capacity on demand, automatic HA, backups, patching and so on, as well as passing responsibility to MS for managing hardware, upgrades and so on. However, for many databases and applications the best route to the cloud is not necessarily obvious. For most, the path of least resistance is IaaS – SQL Server in a Azure VM. It removes the hardware burden but you still have to manage your databases and implementing HA for SQL Server is your responsibility. Also, scaling up comes at quite a cost – the biggest VM (8 CPU cores, 56 GB RAM, 16 1TB drives with 500 IOPS each) weighs in at over over $4500 per month. With PaaS, in the form of Windows SQL Database, you get a “3-copies replica set” so HA comes out-of the box, and removes the majority of the administration burden, but you are moving your database into a very different environment. For a start, it's a shared environment, with other customers using the same compute nodes in the cluster, and potentially even sharing the same database (multi-tenancy). Unless you pay for SQL DB Premium edition, the resources available for your workload will depends on how nicely others “play” in the shared environment. You'll potentially need to do a lot of tuning, and application rewriting to avoid throttling issues, optimising application-database communication to deal with increased latency between the two, and so on. You'll need aggressive application caching. You'll also need retry logic and to deal with (expected) node failure and the need to reconnect. In Tuesday's PASS Summit pre-con from the SQLCAT team, they spent a lot of time covering some of the telemetric techniques (collect into Azure storage the necessary monitoring data) to perform capacity planning, work out the hotspots and bottlenecks in your cloud applications. Tools like WAD (Windows Azure Diagnostics), performance counters SQL Database DMVs, and others, will be essential. Of course, to truly exploit the vast horizontal scaling that is available from the existence of thousands of compute nodes, you'll also need to need to consider how to “shard” your data so Azure can move it between nodes at will. Finding the right path to the Cloud isn't easy, but it's coming. I spoke to people one year ago who saw no real benefit in trying to move their infrastructure and databases to the cloud, but now at their company, it's the conversation that won't go away. Tony.  

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  • Breaking down CS courses for freshmen

    - by Avinash
    I'm a student putting together a slide geared towards freshmen level students who are trying to understand what the importance of various classes in the CS curriculum are. Would it be safe to say that this list is fairly accurate? Data structures: how to store stuff in programs Discrete math: how to think logically Bits & bytes: how to ‘speak’ the machine’s language Advanced data structures: how to store stuff in more ways Algorithms: how to compute things efficiently Operating systems: how to do manage different processes/threads Thanks!

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  • Why no fortran standard library ?

    - by Stefano Borini
    To be a language focused on mathematics and scientific computing, I am always baffled by the total lack of useful mathematical routines in the Fortran standard library. One would expect it to be shipped at least with a routine to compute standard deviation and mean, but this is not the case. In particular with the introduction of Fortran 90 and the addition of modules (thus reducing namespace pollution), I don't see any reason why of this critical lack of services. I would like to hear your knowledge about why this is the case.

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  • Server Systems for SQL Server 2012 per core licensing

    - by jchang
    Until recently, the SQL Server Enterprise Edition per processor (socket) licensing model resulted in only 2 or 3 server system configurations being the preferred choice. Determine the number of sockets: 2, 4 or 8. Then select the processor with the most compute capability at that socket count level. Finally, fill the DIMM sockets with the largest capacity ECC memory module at reasonable cost per GB. Currently this is the 16GB DIMM with a price of $365 on the Dell website, and $240 from Crucial. The...(read more)

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  • Design patterns to avoiding breaking the SRP while performing heavy data logging

    - by Kazark
    A class that performs both computations and data logging seems to have at least two responsibilities. Given a system for which the specifications require heavy data logging, what kind of design patterns or architectural patterns can be used to avoid bloating all the classes with logging calls every time they compute something? The decorator pattern be used (e.g. Interpolator decorated to LoggingInterpolator), but it seems that would result in a situation hardly more desirable in which almost every major class would need to be decorated with logging.

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  • The Running Cost of Azure - MSDN Offer

    - by RobbieT
    Richard recently blogged about getting the Red Gate Labs website onto Azure; it's been running awhile now and, as Richard makes sure the cogs are all turning, I've been trying to track the cost. We decided to launch on Windows Azure as both an exercise in using Azure and also getting to grips with hosting stuff in the cloud. If you have an MSDN subscription then you're eligible for an offer which looks pretty great: What the offer amounted to was a small compute instance, a bunch of storage...(read more)

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  • Largest sphere inside a frustum

    - by Will
    How do you find the largest sphere that you can draw in perspective? Viewed from the top, it'd be this: Added: on the frustum on the right, I've marked four points I think we know something about. We can unproject all eight corners of the frusum, and the centres of the near and far ends. So we know point 1, 3 and 4. We also know that point 2 is the same distance from 3 as 4 is from 3. So then we can compute the nearest point on the line 1 to 4 to point 2 in order to get the centre? But the actual math and code escapes me. I want to draw models (which are approximately spherical and which I have a miniball bounding sphere for) as large as possible. Update: I've tried to implement the incircle-on-two-planes approach as suggested by bobobobo and Nathan Reed : function getFrustumsInsphere(viewport,invMvpMatrix) { var midX = viewport[0]+viewport[2]/2, midY = viewport[1]+viewport[3]/2, centre = unproject(midX,midY,null,null,viewport,invMvpMatrix), incircle = function(a,b) { var c = ray_ray_closest_point_3(a,b); a = a[1]; // far clip plane b = b[1]; // far clip plane c = c[1]; // camera var A = vec3_length(vec3_sub(b,c)), B = vec3_length(vec3_sub(a,c)), C = vec3_length(vec3_sub(a,b)), P = 1/(A+B+C), x = ((A*a[0])+(B*a[1])+(C*a[2]))*P, y = ((A*b[0])+(B*b[1])+(C*b[2]))*P, z = ((A*c[0])+(B*c[1])+(C*c[2]))*P; c = [x,y,z]; // now the centre of the incircle c.push(vec3_length(vec3_sub(centre[1],c))); // add its radius return c; }, left = unproject(viewport[0],midY,null,null,viewport,invMvpMatrix), right = unproject(viewport[2],midY,null,null,viewport,invMvpMatrix), horiz = incircle(left,right), top = unproject(midX,viewport[1],null,null,viewport,invMvpMatrix), bottom = unproject(midX,viewport[3],null,null,viewport,invMvpMatrix), vert = incircle(top,bottom); return horiz[3]<vert[3]? horiz: vert; } I admit I'm winging it; I'm trying to adapt 2D code by extending it into 3 dimensions. It doesn't compute the insphere correctly; the centre-point of the sphere seems to be on the line between the camera and the top-left each time, and its too big (or too close). Is there any obvious mistakes in my code? Does the approach, if fixed, work?

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  • What features does D3D have that OpenGL does not (and vice versa)?

    - by Tom
    Are there any feature comparisons on Direct3D 11 and the newest OpenGL versions? Well, simply put, Direct3D 11 introduced three main features (taken from Wikipedia): Tesselation Multithreaded rendering Compute shaders Increased texture cache Now I'm wondering, how does the newest versions of OpenGL cope with these features? And since I have this feeling that there are features that Direct3D lacks from OpenGL's side, what are those?

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  • Oracle Partner Tier1, inc. Launches the Tier1 Private Oracle Cloud

    - by Catalin Teodor
    Tier1, Inc. announced the availability of the Tier1 Private Oracle Cloud, the most optimized and protected computing environment for Oracle Applications and databases. Leveraging Oracle's Virtual Compute Appliance (VCA) technology, it’s the only virtual environment certified to use Oracle Trusted Partitions – the Tier1 Private Cloud provides the flexibility to license Oracle software on a virtual CPU basis. Read more!

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  • Implementing the Reactive Manifesto with Azure and AWS

    - by Elton Stoneman
    Originally posted on: http://geekswithblogs.net/EltonStoneman/archive/2013/10/31/implementing-the-reactive-manifesto-with-azure-and-aws.aspxMy latest Pluralsight course, Implementing the Reactive Manifesto with Azure and AWS has just been published! I’d planned to do a course on dual-running a messaging-based solution in Azure and AWS for super-high availability and scale, and the Reactive Manifesto encapsulates exactly what I wanted to do. A “reactive” application describes an architecture which is inherently resilient and scalable, being event-driven at the core, and using asynchronous communication between components. In the course, I compare that architecture to a classic n-tier approach, and go on to build out an app which exhibits all the reactive traits: responsive, event-driven, scalable and resilient. I use a suite of technologies which are enablers for all those traits: ASP.NET SignalR for presentation, with server push notifications to the user Messaging in the middle layer for asynchronous communication between presentation and compute Azure Service Bus Queues and Topics AWS Simple Queue Service AWS Simple Notification Service MongoDB at the storage layer for easy HA and scale, with minimal locking under load. Starting with a couple of console apps to demonstrate message sending, I build the solution up over 7 modules, deploying to Azure and AWS and running the app across both clouds concurrently for the whole stack - web servers, messaging infrastructure, message handlers and database servers. I demonstrating failover by killing off bits of infrastructure, and show how a reactive app deployed across two clouds can survive machine failure, data centre failure and even whole cloud failure. The course finishes by configuring auto-scaling in AWS and Azure for the compute and presentation layers, and running a load test with blitz.io. The test pushes masses of load into the app, which is deployed across four data centres in Azure and AWS, and the infrastructure scales up seamlessly to meet the load – the blitz report is pretty impressive: That’s 99.9% success rate for hits to the website, with the potential to serve over 36,000,000 hits per day – all from a few hours’ build time, and a fairly limited set of auto-scale configurations. When the load stops, the infrastructure scales back down again to a minimal set of servers for high availability, so the app doesn’t cost much to host unless it’s getting a lot of traffic. This is my third course for Pluralsight, with Nginx and PHP Fundamentals and Caching in the .NET Stack: Inside-Out released earlier this year. Now that it’s out, I’m starting on the fourth one, which is focused on C#, and should be out by the end of the year.

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  • Ways to serve AWS from another domain

    - by mplungjan
    I have installed Ghost on AWS (it is running node) I very much dislike the URL they gave me http://ec2-nn-nnn-nnn-nnn.us-west-2.compute.amazonaws.com/ghost/ I own a domain and linux hosting (but not a VPS) - what would be a practical way to serve my blog via URLS on my own (sub) domain? I can use php and access .htaccess on my domain - possibly do things on the ASW instance too (let me know what to look for)

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  • Pay in the future should make you think in the present

    - by BuckWoody
    Distributed Computing - and more importantly “-as-a-Service” models of computing have a different cost model. This is something that sounds obvious on the surface but it’s often forgotten during the design and coding phase of a project. In on-premises computing, we’re used to purchasing a server and all of the hardware infrastructure and software licenses needed not only for one project, but several. This is an up-front or “sunk” cost that we consume by running code the organization needs to perform its function. Using a direct connection over wires you’ve already paid for, we don’t often have to think about bandwidth, hits on the data store or the amount of compute we use - we just know more is better. In a pay-as-you-go model, however, each of these architecture decisions has a potential cost impact. The amount of data you store, the number of times you access it, and the amount you send back all come with a charge. The offset is that you don’t buy anything at all up-front, so that sunk cost is freed up. And financial professionals know that money now is worth more than money later. Saving that up-front cost allows you to invest it in other things. It’s not just that you’re using things that now cost money - it’s that the design itself in distributed computing has a cost impact. That can be a really good thing, such as when you dynamically add capacity for paying customers. If you can tie back the cost of a series of clicks to what a user will pay to do so, you can set a profit margin that is easy to track. Here’s a case in point: Assume you are using a large instance in Windows Azure to compute some data that you retrieve from a SQL Azure database. If you don’t monitor the path of the application, you may not know what you are really using. Since you’re paying by the size of the instance, it’s best to maximize it all the time. Recently I evaluated just this situation, and found that downsizing the instance and adding another one where needed, adding a caching function to the application, moving part of the data into Windows Azure tables not only increased the speed of the application, but reduced the cost and more closely tied the cost to the profit. The key is this: from the very outset - the design - make sure you include metrics to measure for the cost/performance (sometimes these are the same) for your application. Windows Azure opens up awesome new ways of doing things, so make sure you study distributed systems architecture before you try and force in the application design you have on premises into your new application structure.

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