Category: Scripts and codes

Chef workstation and a basic cookbook

Since the main jobs of system administrator is to maintain systems, keep repeating ourselves which is kind boring as well as to dig into our memory of previous configurations that we have set up on a machine. No wonder, manual consistency configurations need to be checked on server configurations. It can be thousands of machines. Chef, is just another tool to get rid of these situations. It is a configuration management tool which is written in Ruby and Erlang for IT professional. Compared to Puppet which has only the Workstation and the Derver whilst Chef has three components that are the Chef Server, Chef workstation and Chef Node.

Photo credits: Linode.com
Photo credits: Linode.com

The cookbooks are written on the Workstation, and its then uploaded to the Chef server (service) which will be executed on the nodes. Chef nodes can be physical, virtual or directly on the cloud. Normally, chef nodes cannot communicate directly to the workstation. Let’s not focus on the installation.

Let’s first get into the workstation.

1.On the workstation download and install the Chef client from the client download page. In my case, i am on a Centos7 virtual machine.

[[email protected] ~]# wget https://packages.chef.io/stable/el/7/chef-12.12.15-1.el7.x86_64.rpm

2.After installation, you should notice the four utils already available: chef-apply chef-client chef-shell chef-solo

3. Now, we are going to create a cookbook. Since chef use the DSL – Domain specific language, the file created should end with the extension .rb Here is an example called file.rb. The first line means file resource which means a file is being created. The file resource will manage a file on the machine. The content of the file will be created with the line ‘Hello Tunnelix’

file 'file.txt' do
            content 'Hello Tunnelix'
 end

4. The tool chef-apply can be used to run it as follows:

Screenshot from 2016-08-07 21-49-07

5. You will also noticed that the file.txt has been created in the current directory as the path has not been specified.

Screenshot from 2016-08-07 21-50-24

Tips:

  • If the content of file.rb (refer to point 3) has not been modified and you fire a chef-apply again, you would notice a prompt that its already ‘up to date’ which means that it reduce the disk IO as well as the bandwidth. 
  • A string must be enclosed  in double quotes when using variables. You cannot use a single quote into another single quote. It won’t work!

Chef always check and refer to the resource and attributes in the cookbook to execute an order ; ie to cook a food. The thing is that Chef focus on the DSL with the aim to what the modifications need to be. Chef allows servers to be in a consistent state.


Running a server using Django

Running a server using Django is pretty easy. Django is a high-level Python Web framework that encourages rapid development and clean, pragmatic design. Built by experienced developers, it takes care of much of the hassle of Web development, so you can focus on writing your app without needing to reinvent the wheel. It’s free and open source. – Django.

Screenshot from 2016-04-23 18-59-12

1.To start with you will need to have Python which is already there by default on your linux machine. You will need to install Pip with the command. As i am on a Ubuntu machine im using the following commands.

apt-get install python-pip 

2. I am also running komodo-edit as editor. You easily install it with the following commands

add-apt-repository ppa:mystic-mirage/komodo-edit
apt-get update
apt-get install komodo-edit

3. Then, you will need to install django.

pip install django

4. Point yourself to a directory where you want to create your Django projects with the following commands. You would need to create a project. Here my project name is linuxproject. You would notice that a directory called linuxproject is created.

django-admin.py linuxproject

5. Get into the project directory. Here in my case its linuxproject. You should notice a manage.py file and a directory containing the project.

6. Now, open Komodo-edit. Create a new project in the same directory where your project has been created. Save the Django project with Komodo. It should looks something like this:

Screenshot from 2016-04-23 22-01-27

Save the project. launch the following command from terminal.

python manage.py migrate

Now, you can start your server with the following command

python manage.py runserver

You can now navigate to http://127.0.0.1:8000 In future articles, i will get into details of Django.


Starting up with Python – Part 16 – Last Part

Here we are with the last article “Starting up with Python”. This one will shed some ideas on Working with files, Reading and Writing and Writing lines in Python. You can view all the past Python articles here.

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39. Working with Files

To write to a file is pretty simple. I have the file toto which is blank at /python/toto. After using the close function the phrase hey hackers mauritius is written to toto.

>> fileop=open('/python/toto','w')
 >>> fileop.write('hey hackers mauritius')
 >>> fileop.close()

To read from the file do the following. The number 3 here means 3 byte

>> fileop=open('/python/toto','r')
 >>> fileop.read(3)
 'hey'

If you want to read the whole file, just put nothing inside the read function. Its important to close the function to prevent memory leaks.

>> fileop.read()
 ' hackers mauritius

40. Reading and Writing

Let’s not read line by line. Here is how you read a whole line

>> fileop=open('/python/toto','r')
>>> print fileop.readline()
hey hackers mauritius

You can also read line by line and put it into a list

>> fileop=open('/python/toto','r')
>>> print fileop.readlines()
['hey hackers mauritius\n', 'how are you doing\n', 'what are the new projects?\n']

To create a new file or overwrite a file with some lines do this

>> fileop=open('/python/toto','w')
>>> fileop.write('This is a new LINE\n')
>>> fileop.close()

41. Writing Lines

Let’s now create a list and store it into a temporary variable called listtest. listtest is now a list of all lines in toto.

>> fileop=open('/python/toto','r')
>>> listtest=fileop.readlines()
>>> listtest
['This is a new LINE\n']
>>> fileop.close()

We can also modify the same list. Here [1] is the second line as it starts with 0

>> filelist=open('/python/toto','r')
>>> listtest=filelist.readlines()
>>> listtest
['This is a new LINE\n', 'this is another line\n']
>>> filelist.close()
>>> listtest[1]="this is second line"
>>> listtest
['This is a new LINE\n', 'this is second line']

However, this has not been saved to the file. Let’s see how to save it.

>> filelist=open('/python/toto','w')
>>> filelist.writelines(listtest)
>>> filelist.close()

 

 


Starting up with Python – Part15

If you have been following the Python articles since some days, you would have noticed that things are getting more interesting. In case, you have missed the past articles here is a recap. In this article, i will get into Constructors, Import modules, reload modules and Getting modules info.

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35. Constructors

When an object is created, the methods need to be called but when a contructor is when the first object is created, the objects are automatically called.

Lets see a basic method and object analogy

>> class hackers:
... def mauritius(self):
... print "hackers mauritius"
... 


>> obj=hackers()
>>> obj.mauritius()
hackers mauritius

However, in constructors we want to automatically call the object.

In this example, you would notice a class called new and a method called __init__

>> class new:
... def __init__(self):
... print "hackers mauritius"
... print "this is a constructor"
... 
>>> newobject=new()
hackers mauritius
this is a constructor

36. Import Modules

In python, you can write modules and each time you can call it from anywhere in your code. So let’s create a module.

I created a file called hackers.py with the following simple data.

# cat hackers.py 
def testmod():
 print "this is hackers Mauritius"

This is how you can import different modules imported from a file. Modules can also be imported once per file.

>> import hackers
>>> hackers.testmod()
this is hackers Mauritius

37. Reload modules

However, if the source file is edited and you would import the same module, the result would be the same. To get result from the source file, use this parameter

>> import hackers
>>> hackers.testmod()
this is hackers Mauritius
>>> reload(hackers)
<module 'hackers' from 'hackers.py'>
>>> hackers.testmod()
this is hackers Worldwide

38. Getting modules info

To get modules info, there are in build module. For example, there is an inbuilt module called SQRT

>> import math
>>> math.sqrt(25)
5.0

To know what the module math contains, you can use the dir function

>> dir(math)
['__doc__', '__name__', '__package__', 'acos', 'acosh', 'asin', 'asinh', 'atan', 'atan2', 'atanh', 'ceil', 'copysign', 'cos', 'cosh', 'degrees', 'e', 'erf', 'erfc', 'exp', 'expm1', 'fabs', 'factorial', 'floor', 'fmod', 'frexp', 'fsum', 'gamma', 'hypot', 'isinf', 'isnan', 'ldexp', 'lgamma', 'log', 'log10', 'log1p', 'modf', 'pi', 'pow', 'radians', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'trunc']

There is also the help function. You just need to type this

>> help(math)

You would noticed  a list of what each modules does. However, before using a module you can use this 

>> math.__doc__
'This module is always available. It provides access to the\nmathematical functions defined by the C standard.'

It gives a quick summary of what the module does.

 

 


Starting up with Python – Part14

Welcome to another Python article on Subclasses / Superclasses. I will also get into Ovewrite Variable on Sub as well as Multiple Parent Classes. Here is a mind map of all articles related to Python.

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32.Subclasses

This is interesting when you can inherit a single parent class from a class.

>> class parentClass:
… var1=”country”
… var2=”region”

>>> class childClass(parentClass):
… pass

>>> parentObject=parentClass()
>>> parentObject.var1
‘country’
>>> childObject=childClass()
>>> childObject.var1
‘country’
>>> childObject.var2
‘region’

33. Overwrite Variable on Sub

We will now try to overwrite variable on subclass. I will create a parent class called hackers and the child class called project.

>> class hackers:
… var1=”country”
… var2=”age”

>>> class project(hackers):
… var2=”skills”

Let’s access var2 from the parent and the child.

>> parentobject=hackers()
>>> childobject=project()
>>> parentobject.var1
‘country’
>>> childobject.var2
‘skills

As we can see now if we try to overwrite its just by calling the variable in the class

>> childobject.var1
‘country’

This is cool if you have one huge class and if you want to change some few things in it.

34. Multiple Parent Classes

This is straight forward to use different items just by adding the name of your classes in your parameter.

>> class hackers:
… var1=”Mauritius”

>>> class skills:
… var2=”devops”

>>> class best(hackers,skills):
… var3=”we are hackers”

>>> childObject=best()
>>> childObject.var1
‘Mauritius’
>>> childObject.var2
‘devops’
>>> childObject.var3
‘we are hackers’