Posts - Page 7 of 10

More ActiveAdmin Customizations with CanCan

Post author By Yoav Aner
Post date 10 August, 2012

Coming from Django, I was a little surprised/disappointed that permissions aren’t very tightly integrated with the Rails ActiveAdmin as they are with the django admin. Luckily, my search for better authorization for ActiveAdmin has led me to this very informative post by Chad Boyd. It makes things much easier so we can authorize resources more flexibly.

However, there were a couple of aspects that I still wasn’t 100% happy with:

When an unauthorized action is attempted, the user is simply redirected with an error message. I personally like to return a 403 response / page. Yes, I’m nitpicking. I know.
Default actions like Edit, View and Delete still appear. They are not dependent on the permission the user has. Clicking on those won’t actually allow you to do anything, but why have some option on the screen if they are not actually allowed??

So with my rather poor Ruby/Rails skill, and together with my much more experienced colleague, we’ve made a few tweaks to the proposal on Chad’s post to make it happen.

rails ruby Security Technology

Simple Detection of Comment Spam in Rails

Post author By Yoav Aner
Post date 4 August, 2012

It’s always nice to be able to get some feedback, or for users to make a contact via a simple Contact form. However, it didn’t take too long before spammers started hitting those forms too. It was quite interesting to see the kind of messages we started receiving. In a way, most of those submissions were more like stories, or snippets from an email to a friend. They didn’t have any of those very much expected keywords for fake watches or erectile dysfunction enhancers. Many didn’t even have any links either. So what were these messages then? My personal guess was that these were some kind of a reconnaissance attempts. The bots were sending innocent messages first to various online forms. Then I imagine they will crawl the site more, trying to see if those submissions appear elsewhere. If/when they do, they will hit those forms hard with the real spam content. In any case, these were all speculations that I didn’t really care to prove right or wrong. I just wanted to get rid of this junk. Fast.

linux Performance Technology

Bootstrap cloud shoot-out part II

Post author By Yoav Aner
Post date 20 July, 2012

A recent comment by Martyn on my cloud performance shoot-out post prompted me to do another round of testing. As the bootstrap process I described on the last post evolved, it’s always a good idea to test it anyway, so why not kill two birds with one stone? The comment suggested that the Amazon EC2 micro instance is CPU throttled, and that after a long period (in computer terms: about 20 seconds according to the comment), you could lose up to 99% of CPU power. Whereas on a small instance, this shouldn’t happen. So is EC2 small going to perform way-better than the micro instance? How is it going to perform against Linode or Rackspace equivalent VPS?

linux monitoring network Technology wordpress

Webfaction fail. over.

Post author By Yoav Aner
Post date 15 July, 2012

This post starts as a rant about webfaction, but somehow turns into a rave. I recently discovered (the hard way) that I can failover almost any site to a secondary host in a different data centre, all with a few scripts on a webfaction shared hosting account.

django monitoring python Technology

Fabric Installer for Graphite

Post author By Yoav Aner
Post date 1 May, 2012

fabric-graphite is a fabric script to install Graphite, Nginx, uwsgi and all dependencies on a debian-based host.

Why?

I was reading a few interesting posts about graphite. When I tried to install it however, I couldn’t find anything that really covered all the steps. Some covered it well for Apache, others covered Nginx, but had steps missing or assumed the reader knows about them etc.

I’m a big fan of fabric, and try to do all deployments and installations using it. This way I can re-run the process, and also better document what needs to be done. So instead of writing another guide, I created this fabric script.

linux Performance Technology

bootstrap shooting at the clouds

Post author By Yoav Aner
Post date 9 April, 2012

One of my primary aims when building a resillient cloud architecture, is being able to spawn instances quickly. Many cloud providers give you tools to create images or snapshots of existing cloud instances and launch them. This is great, but not particularly portable. If I have one instance on Linode and I want to clone it to Rackspace, I can’t easily do that.

That’s one of the reasons I am creating bootstrap scripts that completely automate a server (re)build process. Given an IP address and root password, the script should connect to the instance, install all necessary packages, pull the code from the repository, initialize the database, configure the web server and get the server ready for restore of user-data.

I’m primarily using fabric for automating this process, and use a standard operating system across different cloud providers. This allows a fairly consistent deployments across different providers. This also means the architecture is not dependent on a single provider, which in my opinion gives a huge benefit. Not only can my architecture run on different data centres or geographic locations, but I can also be flxeible in the choice of hosting providers.

All that aside however, building and refining this bootstrapping process allowed me to run it across different cloud providers, namely: Rackspace, Linode, and EC2. Whilst running the bootrstrapping process many times, I thought it might be a great opportunity to compare performance of those providers side-by-side. My bootstrap process runs the same commands in order, and covers quite a variety of operations. This should give an interesting indication on how each of the cloud providers performs.

optimization Technology wordpress

How much (cache) is too much?

Post author By Yoav Aner
Post date 17 March, 2012

One of the best rules of thumb I know is the 80/20 rule. I can’t think of a more practical rule in almost any situation. Combined with the law of diminishing returns, it pretty much sums up how the universe works. One case-study that hopes to illustrate both of these, if only a little, is a short experiment in optimization I carried out recently. I was reading so many posts about optimizing wordpress using nginx, varnish, W3-Total-Cache and php-fpm. The results on some of them were staggering in terms of improvements, and I was inspired to try to come up with a similar setup that will really push the boundary of how fast I can serve a wordpress site.

Spoiler – Conclusion

So I know there isn’t such a thing as too much cash, but does the same apply to cache?

Security

A different kind of spider

Post author By Yoav Aner
Post date 11 February, 2012

It’s always nice to discover a new tool or service that does things differently. Even if just a little. I remember when someone first told me about hipmunk. Just when I thought all flight search websites are pretty much the same, here’s one example of something different.

Arachni

Perhaps this wasn’t as obviously different as hipmunk is, but one of the tools I came across recently within the security testing world is Arachni. A number of things made it stand out a little. First of all, it is written in Ruby. That already sparked some curiosity. I’m not entirely sure why, but I guess I’m naturally more interested in programs and tools in Ruby and Python. The next thing that was evidently different from other web scanners was the fact that Arachni seems to be very pluggable and interface-able. Arachni appears to be geared towards interfacing with external scripts or programs though an API. One of its core features is its distributed architecture, allowing to launch many modules independently and control them programmatically.

After playing around with it, I came across some issues and couldn’t make it work as I expected. Most of them out of my own lack of knowledge or being lazy reading through the extensive documentation. Luckily, it didn’t take more than a few minutes after posting a question on github, that I received a response from Arachni’s creator, Tasos Laskos, aka Zapotek.
After chatting with Tasos a few times via email, I became even more intrigued about him and the project. I then decided it would be interesting to interview him for my blog. I have no experience interviewing people, but what the heck.

Tasos accepted my invitation for an interview, with the condition that it must be a text-based interview. So this interview was carried out via email alone. I personally suspect his voice is funny, but he (obviously) denied it :)
Tasos is certainly not an ordinary person. It becomes apparent when you read his blog, or even the documentation for Arachni. As you could see from the interview, Tasos appears to have very strong and clear opinions. He doesn’t mince his words, and very directly expresses what he thinks. Nevertheless, Tasos and Arachni seem to be doing something a little different, and there’s definitely more to wait for.

linux Security

updating lighttpd on debian squeeze against the BEAST

Post author By Yoav Aner
Post date 11 February, 2012

If you’re updating your debian stable (squeeze) and using Lighttpd as your web server, you might come across a security notice on how to fix your lighttpd against the BEAST attack.

lighttpd (1.4.28-2+squeeze1) stable-security; urgency=high

 This releases includes an option to force Lighttpd to honor the cipher order
 in ssl.cipher-list. This mitigates the effects of a SSL CBC attack commonly
 referred to as "BEAST attack". See [1] and CVE-2011-3389 for more details.

 To minimze the risk of this attack it is recommended either to disable all CBC
 ciphers (beware: this will break older clients), or pursue clients to use safe
 ciphers where possible at least. To do so, set

 ssl.ciphers =  "ECDHE-RSA-AES256-SHA384:AES256-SHA256:RC4:HIGH:!MD5:!aNULL:!EDH:!AESGCM"
 ssl.honor-cipher-order = "enable"

 in your /etc/lighttpd/conf-available/10-ssl.conf file or on any SSL enabled
 host you configured. If you did not change this file previously, this upgrade
 will update it automatically.

 [1] http://blog.ivanristic.com/2011/10/mitigating-the-beast-attack-on-tls.html

There’s a mistake on this note however. Instead of

django optimization python Security

Keep your hands off my tastypie

Post author By Yoav Aner
Post date 26 January, 2012

Update

Please note that since Tastypie v0.9.12 the authorization framework was rewritten. Lots of information on this post no longer applies. I’m hoping to write a follow-up post at some stage.

Original Post

I’ve been using tastypie, the very awesome django REST API framework for a little while now (btw, that’s not the official title, but it might as well be). I’m not going to write yet another comparison between tastypie and django-piston. My reasons for choosing tastypie were that its code looked nicer, and it seemed a much more active project.

One of the things that I immediately liked about tastypie, being a security-geek and all, was the security framework built into it. Primarily the authentication and authorization classes. They make it very easy to extend, and almost a no-brainer to apply to any resource. This means that providing resource-level authorization is also very easy and clean.

However, whilst working with tastypie and applying some authorization rules to my resources, I noticed a couple of pitfalls. Those are quite easy to miss if you’re not very familiar with the tastypie codebase. I wouldn’t say it’s a vulnerability or a bug as such, perhaps more of a (sub-optimal) design choice from a security-perspective. That said, if you use tastypie incorrectly, or unaware of those pitfalls, you might create a security vulnerability on your otherwise delicious API.