Posts tagged: apache

Generate a self-signed certificate

By , Monday 20th May 2013 9:21 am

Quickly generate a self-signed certificate on the command line. Noting this information as the original source has disappeared and its handy to have around.

mkdir -p /etc/certs
openssl req -new \
            -x509 \
            -days 3650 \
            -nodes \
            -out    "/etc/certs/EXAMPLE.COM.pem" \
            -keyout "/etc/certs/EXAMPLE.COM.key" \
            -batch -subj "/CN=EXAMPLE.COM"

# ensure that the files are readable 
chmod o+r /etc/certs/EXAMPLE.COM.*

Apache proxy with digest authentication

By , Sunday 27th March 2011 12:57 pm

This post will quickly show you how to set up proxying with basic authentication using apache.

In my case I wanted to have transmission bit torrent client available over the internet so I could check on the state and adminster torrent downloads (such as the latest fedora release) as required. Transmission itself runs its web client on port 9091 by default. Rather than bother opening up more ports on my firewall and adding the nessecary port forwarding rules I decided I’d just proxy the calls through to transmission via apache using mod_proxy.

Continue reading 'Apache proxy with digest authentication'»

Office Grid Computing using Virtual environments – Part 5

By , Friday 4th December 2009 11:03 pm


I work in a company where we run many batch jobs processing millions of records of data each day and I’ve been thinking recently about all the machines that sit around each and every day doing nothing for several hours. Wouldn’t it be good if we could use those machines to bolster the processing power of our systems? In this set of articles I’m going to look at the potential benefits of employing an office grid using virtualised environments.

In Part 4 we looked at using tools to ensure that we’re running the latest version of the code and data sources so that obtained results are always up-to-date with the latest business information and logic.


Before deploying your grid system if there’s one thing you do and one thing alone it’s benchmark your current system! No matter what you tell colleagues about how much extra work your system is going to do unless you have numbers to back this up your guarantees are nothing. So,

  • how many records can you process currently? Per Day? Per Hour?
  • How long does it typically take to turn around a job?
  • How much more capacity do you have?

There’s also additional questions:

  • If your processing server (or one of your processing servers) goes down how will this affect your capabilities, will you be crippled?
  • What advantages do you hope/expect to get from a grid system?
  • Are your office machines capable of running the jobs?
  • Are your (or can you jobs be converted) to wrok in this style of running?

The last major point is to take your time on any major change like this. Update your processing code to work using the new methodology, benchmark again. Possibly set up your processing server to run a virtual machine, after all your processing server will just be another worker (just a very powerful one relatively). Allow the new process to settle.


My suggestion would be to pop into the office one weekend perform all the installations and setup. Do this just before a fortnight’s holiday and leave so other poor chap to deal with the consequences… maybe not…

Deployment for a system like this needs to be slow. Despite it being relatively simple to set up this system will affect your entire office infrastructure (well the digital one). Firstly, roll out to a couple of machines at a time, monitor network traffic, how the worker hosts perform on a day-to-day basis. You may need to alter your job configuration in response to your findings.

Once the system has settled with a few machines (lets say 10% of all office machines, i.e. 5) keep monitoring network traffic and host machine performance.  Next benchmark again, you should now be processing 33% more jobs than your first benchmarks. Check this is so, or that you’re at least in this ballpark. If not, investigate what is going on before moving on. Repeat this cycle until you happily have all office machines running without killing individual machine performance or grinding your network to a standstill.

At all times keep benchmarking, even after all deployments are made. Check how new code updates affect speed of your system, check all workers are reporting in and processing jobs. Slowly (very slowly) increment your job configuration to get the best from your workers and network.


What if you want to stop your workers from running at some time? They are all out there running, regenerating, and trying their best to process data like hungry insects. The answer may seem obvious but its worth adding just in case its overlooked. Simply edit your processing script with an exit(0) or die() or some other statement to kill your processing job. An important reason why we always try to update to the latest processing script before any run!

Demonstration System

In order to write this set of short articles I created a very small grid to demonstrate the technologies and methodologies. I read lots of articles, tutorials, and used various tools to setup and monitor what was going on. By no means have I gone out and saturated a whole office with traffic and nor have I had access to a regular staff members PC to see how host performance was affected.

My demonstration system was very humble indeed. I used my regular desktop set up as a job control server. On this I had installed mySQL server installed set up as a master in replication, PHP,  and SVN linked through apache (for access via worker VM).

I then created a centOS worker machine on VirtualBox on a 6 year old windows XP laptop. I setup scheduled tasks as specified after copying the VM onto the machine and let it go.

The virtual machine was set up with PHP, subversion, and mySQL. I checked out a branch named ‘worker’ from my job control servers repository and made sure it could be updated using ‘svn update’. Next I setup mySQL as a slave and checked that data was replicating from mySQL on the job control server down to the worker VM. After all this I setup the bash script and the cron job.

My processing script basically went along the lines of this (very simple stuff):

  • Read in the name field
  • Counted the number of similar names in a table from the data source held on the VM
  • Counted the number of names as above but splitting the name by spaces (i.e. forename, middle, surname)
  • Repeated this process 1,000 times

Each job took approximately 20 minutes to run. At one point I opened several copies of the worker VM on the windows laptop and watched the jobs be checked off by each of the worker IP addresses. At this point I also confirmed that replication automatically restarted.

Leaving the laptop to idle resulted in a worker starting to process jobs from the job control server. When resuming laptop usage there was a delay of about 30-60 seconds, this is a fair amount of time and staff would need to be made aware that their machine may pause for a short while when returning to the machine. Newer machines may not have a pause of this long. The benefit of the amount of processing performed by these machines during idle periods would more that outweigh staff members having to wait a short period (say 1 minute) on arriving at their machines of a morning (I frequently wait longer that this for a Windows Defender update to take place) provided they were made aware of this (useful time to grab a morning coffee!).

Overall I feel confident that I have demonstrated the technologies that could be used to create such a system. I have shown that such a system does work on a (very) small scale and with some more experimenting could be scaled up utilise the resources of an office’s machines. If I don’t get to the point of doing this I would be very interested to know/see when someone else does.

Conclusions / Evaluation

The next obvious step would be to actually get a real world example and start to deploy a system such as this within an office environment and see what happens. Asking a business to commit to this without a trail blazing company to prove the technology and effectiveness may be a little difficult. Grid/Distributed computing is very popular is some circles and has some large applications (BIONC, SETI@Home, Folding@Home, etc). I did not, however, find a smaller scale and simple system like this in my searches that could be rolled out within an office environment.

I created a basically free system using mostly open source software and tools available in almost any office. The technologies were basically demonstrated and show to perform and work as expected. Hopefully I have show that with not much work and with a very simple setup you can deploy an office grid computing system that is powerful, cheap,  and scalable all at the same time.

Once a system is up and running there is almost no end to the amount of customisation and improvements you can make. For example statistics / benchmarking can easily be added showing the worth of such a system every day. New machines can be added quickly and easily as and when they arrive with upgrades to existing hardware bolstering your processing power.

I hope you’ve enjoyed reading this series of articles and its given you food for thought on running an office grid system. The solution presented here won’t necessarily work in all situations but should be adaptable to allow you to get your data processing done using your own solution.

Please feel free to send me any comments, corrections, or improvements and I’ll do my best to keep this article updated to match.

[notice] child pid XXXX exit signal Segmentation fault (11)

By , Sunday 11th October 2009 6:09 pm

If you’ve recently upgraded PHP or Apache you maybe coming up against the issue of your webserver returning blank pages, and throwing error messages into your logs with no idea why, here’s one possible way to fix it…

I’ve had this problem a couple of times recently after upgrading Apache or PHP on a virtual machine. The first time I noticed the error I simply reverted to a backup of my VM but the second time I realised I’d have to look into the issue.

The first time I noticed the issue some of my web pages were being served as blank files while the others worked absolutely fine. After some investigation I noted that apache was writing out to /var/log/http/error_log with the following message repeatidly:

[notice] child pid XXXX exit signal Segmentation fault (11)

There’s not allot to go by on-line, and most of the pages about it trail off to nothing. That said, I narrowed down the issue to PHP crashing when trying to unneeded dynamic libraries.

Looking at my php.ini (/etc/php.ini) I commented out all of the dynamic libraries loaded planning on commenting them back in as required. The two I had to take out where and

Once these were removed all my web pages were being served fine, just as before the PHP/Apache update.

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