Category: Computers

Things dealing with the wonderful world of IT – software, hardware, cloud computing, or anything else that might fit.

Installing Heartbeat on Amazon’s EC2

I am currently working on setting up a small high availability server cluster on Amazon’s EC2 cloud. Such a setup requires several underlying technologies to work together. Common among these are a distributed file system, a load balancer, and some form of monitoring and resource control. This article looks at the one aspect of ‘monitoring’… Continue reading Installing Heartbeat on Amazon’s EC2

Rotating EBS Snapshots: ec2-prune-snapshots

Following the significant disruption of EBS volumes in April, the importance of backups was once again brought to the forefront. Amazon’s method of generating EBS backups is the ‘snapshot’ – a differential backup stored in S3. While Amazon provides tools for creating snapshots (either command line, or via their API), a script that is quite… Continue reading Rotating EBS Snapshots: ec2-prune-snapshots

VirtualStore – A few more hidden files

Having not used Windows 7 much (and having skipped over Vista), I was rather surprised to discover that I was unable to locate files that were saved by a particular program. In this case, the program saved the files in its application folder, under %programfiles%. Now, having no clue about the virtualization in effect, I… Continue reading VirtualStore – A few more hidden files

Generating a pure-ftpd RPM for Amazon’s Linux

The only ftp server the amzn repository has is vsftpd. While, as the name suggests, vsftpd is supposed to be ‘very secure’ many other ftp servers have a comparable track record for security. Of these, pure-ftpd is easily configured and offers a wealth of features. Pure-FTPd is easily configured, and as it comes with an… Continue reading Generating a pure-ftpd RPM for Amazon’s Linux

ec2-consistent-snapshot on Amazon’s Linux AMI

Update: the complementary article to this one, on Rotating EBS snapshots has now been posted. After the recent failure of EBS volumes on Amazon’s cloud, backup is quite likely something to be considering. If, during the aforementioned incident, recent snapshots of the affected EBS volumes were available, it might have been possible to relaunch instances… Continue reading ec2-consistent-snapshot on Amazon’s Linux AMI

Rebuild Icon Cache

Recently, after upgrading a program (FileZilla in this case), the program’s icon would not display on the desktop (Windows 7). Even deleting and recreating the shortcut resulted in a broken icon (although, the shortcut itself worked fine). No amount of refreshing the desktop made a difference. The quick fix was to rebuild the icon cache,… Continue reading Rebuild Icon Cache

DKIM/Domainkeys signing via DKIMproxy

With the ever increasing volume of SPAM being transmitted, many email services look toward more elaborate ways to authenticate email. Beyond the obvious – content – two commonly used methods (perhaps with some variations), include sender policy framework (SPF), and DomainKeys Identified Mail (DKIM). Both of these require the use of DNS records to function.… Continue reading DKIM/Domainkeys signing via DKIMproxy

Prime Factoring with PHP

A surprisingly large number of math based computer problems appear to require factorization, finding prime number, or prime factoring. Presented below is a reasonably fast algorithm for prime factoring a number – it is limited to the integer size on PHP (231-1). It should be a fairly trivial exercise to modify the function below to… Continue reading Prime Factoring with PHP

Setting up Subversion

Subversion is a versatile version control system. This article looks at how to set up subversion on Amazon’s Linux (RHEL/CentOS derived), and the necessary setup for using it with Apache (proxied through Nginx), as well as the setup of a repository, and the use of hooks to automatically update a live (non-production) working copy. Basic… Continue reading Setting up Subversion

Setting up NodeJS

It is quite unfortunate that one only has a finite number of hours to dedicate to learning new things, for inevitably there are things we skim over, or worse yet, don’t even know exist. Today, as I was looking for efficient ways of implementing server push for a project of mine, I came across NodeJS.… Continue reading Setting up NodeJS

Setting Windows’ Time Service’s Update Frequency

There are some instances when it is desirable to change the default interval between synchronizations by the Windows Time Service (i.e. NTP). For instance, I recently encountered a computer where the clock would run a few seconds fast each day (it was not a battery problem), for a quick fix, it was easy to simply have the… Continue reading Setting Windows’ Time Service’s Update Frequency

Escalating Consequences with IPTables

I have previously written a bit about using IPTables to limit brute-force attacks. For the past month, that system has been working quite well. The typical attack pattern resembled that in [graph 1, graph2]. A few days ago, however, an attack was implemented which ‘fell under the radar’, so to speak – instead of being… Continue reading Escalating Consequences with IPTables