Wednesday, September 14, 2011


you are so cool.

require 'rubygems'
gem 'nokogiri'
require 'nokogiri'

xml = <<-EOXML

doc = Nokogiri::XML(xml)
ps = doc.xpath('//p')

@p = ps.first
def take field

puts "phone: #{take :phone}"
puts "fax: #{take :fax}"

$ ruby nokogiri-xpath.rb
phone: 12345
fax: 67890

Wednesday, August 31, 2011

rvm and ree 1.8.7 on wheezy

(actually it is on Linux Mint Debian, but should be the same afaik)

so you want to do this:
but for ree 1.8.7?

Then here is the patch for you.


* patch built with
diff -crB
and edited manually

* rvm puts sources in ~/.rvm/src

Saturday, August 27, 2011

Unexpected offering order for ssh keys on Linux Mint Debian

I've many different ssh keys in ~/.ssh, which I used happily through .ssh/config or -i option on Debian Lenny.

Recently I've installed Linux Debian Mint and I was no longer able to access some hosts. The reason was that ssh is offering all the keys in ~/.ssh without giving precedence to the specified key. So, ssh may disconnect for "Too many authentication failures" if the right key happens to be at the bottom of the list.

My workaround was to move most keys in another directory, and update .ssh/config and scripts accordingly.
It works but I'm not fully satisfied with it.

Friday, September 3, 2010

EC2 and its goodness

Recently, together with my favourite system administrator Emanuele, I had the occasion to migrate a small size structure to EC2. Actually Emanuele did most of the work but I believe my contribute was important too :-) .

We wanted to keep the base costs as low as possible and, at the same time, have a system able to scale on traffic peaks. Moreover we wanted a system easy to upgrade and adapt to the changing requirements. Not much original indeed.

I believe that the final result is quite interesting and I want to summarize it here.

We have an ELB and a main instance behind it. The instance is able to serve the web sites alone but when necessary the system can add additional application servers to help it.

System configuration is done with chef and poolparty so we can terminate it and create a new one in minutes. That's especially useful to create a temporary staging environment to test new upgrades.
Applications deployments is done in the same way and we can host many distinct applications on the same cloud.

Scaling triggers didn't fulfill well our requirements, so we fall back implementing a monitor script that leverages AWS service and controls how we scale up and down the system. This script allows us non-linear scaling (i.e. scaling up or down a variable number of instances depending on situation) and to consider many metrics in scaling conditions.

Although AWS has added support for configurable reverse DNS records since March 2010 we still think it is advantageous to delegate emails delivery to Google Apps. Postfix relays outgoing emails to Google smtp servers using the credentials associated to the sender of the message.
To cope with Google Apps limits we record the number of messages sent by an address and we can switch to another address of the same type in case we reach a predefined quota. For example we can send thousand messages with and then send other thousand messages with and so on.

To speed up the initialization of a new application server we can create and use a custom AMIs which are almost ready to run. That doesn't conflict with chef which is able to skip already done
configuration steps and to quickly complete the setup.
Updating the auto-scaling group in order to use the new AMI is a bit tricky but can be done without affecting the production system or the ELB and related CNAME DNS records.

System backups are based on EBS snapshots. We create monthly, weekly, daily and 3-hourly snapshots and we prune the oldest ones of any type independently.

That's all folks, add a comment if you want to know more.

Saturday, June 26, 2010

Twitter XAuth for Ruby scripts

This post explains very well what is going on:

Now, if you have a script to post to Twitter everytime an item is added in your Ruby CMS, you are wondering how to apply what Steve Reynolds suggests, aren't you?

1. register a Twitter application,
2. ask Twitter team to enable XAuth in such application. They'll enable it for a limited period of time.
3. use XAuth to create as many OAuth access tokens you need:
require 'oauth'
consumer = consumer_key, consumer_secret, {:site => ''}
hash.each do |k, v|
puts k
token = consumer.get_access_token(nil, {},
:x_auth_username => v[:username], :x_auth_password => v[:password], :x_auth_mode => client_auth')
puts %Q(
:oauth_access_token => '#{token.token}',
:oauth_access_secret => '#{token.secret}'
puts "exception: #{$!.message}"
puts '-----'
4. store the tokens everywhere you like (I casted them in an initializers)
5. initialize your Twitter client using OAuth and the stored tokens, for example:
auth =, consumer_secret)
auth.authorize_from_access(@opts[:oauth_access_token], @opts[:oauth_access_secret])
twitter =

Tuesday, April 6, 2010


I don't have much motivation and time to blog but at least the blog is ready :-)