Kevin Tran duykhoa

Virtual Hosts on nginx (CSC309)

When hosting our web applications, we often have one public IP address (i.e., an IP address visible to the outside world) using which we want to host multiple web apps. For example, one may wants to host three different web apps respectively for example1.com, example2.com, and example1.com/images on the same machine using a single IP address.

How can we do that? Well, the good news is Internet browsers

Chapter 1 - Object Oriented Design

The purpose of design is to allow you to do design later, and it's primary goal is to reduce the cost of change.

SOLID Design:

Single Responsibility Principle: a class should have only a single responsibility
Open-Closed Principle: Software entities should be open for extension, but closed for modification (inherit instead of modifying existing classes).
Liskov Substitution: Objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program.
Interface Segregation: Many client-specific interfaces are better than one general-purpose interface.

Puppet Cheat Sheet

Validate manifests

Puppet Lint

http://puppet-lint.com/

Installing of Fedora:

Description

This simple script will take a picture of a whiteboard and use parts of the ImageMagick library with sane defaults to clean it up tremendously.

The script is here:

#!/bin/bash
convert "$1" -morphology Convolve DoG:15,100,0 -negate -normalize -blur 0x1 -channel RBG -level 60%,91%,0.1 "$2"

Results

Opening and closing an SSH tunnel in a shell script the smart way

I recently had the following problem:

From an unattended shell script (called by Jenkins), run a command-line tool that accesses the MySQL database on another host.
That tool doesn't know that the database is on another host, plus the MySQL port on that host is firewalled and not accessible from other machines.

We didn't want to open the MySQL port to the network, but it's possible to SSH from the Jenkins machine to the MySQL machine. So, basically you would do something like

ssh -L 3306:localhost:3306 remotehost

In Rails 3

NOTE: This post now lives (and kept up to date) on my blog: http://hakunin.com/rails3-load-paths

If you add a dir directly under app/

Do nothing. All files in this dir are eager loaded in production and lazy loaded in development by default.

If you add a dir under app/something/

Setting up a SSL Cert from Comodo

I use Namecheap.com as a registrar, and they resale SSL Certs from a number of other companies, including Comodo.

These are the steps I went through to set up an SSL cert.

Purchase the cert

Each of these commands will run an ad hoc http static server in your current (or specified) directory, available at http://localhost:8000. Use this power wisely.

Discussion on reddit.

Python 2.x

$ python -m SimpleHTTPServer 8000

	require 'fileutils'

	desc "Create nondigest versions of all ckeditor digest assets"
	task "assets:precompile" => :environment do
	fingerprint = /\-([0-9a-f]{32})\./
	for file in Dir["public/assets/ckeditor/*/"]
	# Skip file unless it has a fingerprint
	next unless file =~ fingerprint

	# Get filename of this file without the digest

	require 'mina/bundler'
	require 'mina/rails'
	require 'mina/git'
	require 'mina/rvm'

	# Usually mina focuses on deploying to one host and the deploy options are therefore simple.
	# In our case, there is a number of possible servers to deploy to, it is therefore necessary to
	# specify the host that we are targeting.
	server = ENV['server']
	# Since the same host can have multiple applications running in parallel, it is necessary to