There are three basic constraints:
1)How to apply conditions?
2)How to use loops,for that,what is the syntactical
structure we need to follow.
3)And how do you define variables and all other stuff in
ruby?
You can take this and directly apply in your recipe.
(ruby has programming language strength directly).
one is chef
documentation for ruby.
other one is:
ruby on windows
>> rubyinstaller for
windows. (google)
$ruby –v
and do
irb (Interactive
ruby,you can extract the interactions of the ruby over here).
Why do I need to
learn ruby?
Ansible internally
uses python ---. WE WRITE HERE PLAYBOOK
(WHICH MAY HAVE THERE,OWN LANGUAGE TO DEFINE THINGS)
Puppet internally
uses ruby à WE WRITE HERE MANIFESTS (WHICH MAY HAVE
THERE,OWN LANGUAGE TO DEFINE THINGS)
Where as in chef,you
directly ruby.
It is very easy to write ruby syntaxies.
Yum install httpd
Apt-get install
apache2
Some resource called
package.
-à
package ‘httpd: (centos) when run in redhat,this line should
be executed.
à package
‘apache2: (Ubuntu) ) when run in
debian,this line should be executed.
For these kind of loop,how do we control in loop.
(Generally,when you come with the programming language,all
of the 1o lines will be executed one after the other).
How to start the
services?
Service httpd start
Service apache2 start
If you want package for 10 times,you wont write package for
10 times,it’s a bad practice.you iterate the one package.
Where are ruby files
used?
Recipes is the place,where we use the ruby.
Attributes,roles,environment we use ruby in all these
places.
How to execute all the lines of the code.(write
syntaxies,that will execute one-after the other.
How to choose between the lines of the code.
FOR EXAMPLE:
A
B
C
D
If you want to execute all the four.
(but there will situations,where you want to execute
A,B and D,you want to skip C).
because for example it is RedHat.
(but there will situations,where you want to execute
A,B and C,you want to skip C).
because for example it is Debian.
One some cases,you want to execute A and B for 10times and C
for 15times.
How do you control
these executions?
We need to control the executions.
How do you maintain
this?
This is equivalent to the shell scripting.
Ruby is beyond that,there is a rubygem. (not covered)
We are getting in to key basic constraints of programming.
***** We are just
controlling the execution of lines:
whatever the
programming,we write,it will use read memory.
(do they use RAM or
do they use hard disk??).
RAM
Why do they RAM?
Because,harddisk is not meant for executions.(harddisk is
meant for storage).
Whenever your program executes.Memory will be created and
whatever values you give will be store in the memory.
Generally,if you know the RAM:
RAM Is nothing but a
slot of address spaces.
It will have,many address locations.(in hexadecimal).
For example,
If you want to store the 10,it will look the
address,something like this:
Xof334f
This might be the
address of your variable,where your storing.address of the data,wherever your
storing.
And everytime,this address is changed.
(you cannot get the same addresses on every machine).
Is it possible,to access the memory of the RAM by its
address,I don’t think so,we have that option,because it is quite dynamic,In my
machine,if I am running the game and launching my application,my execution will
be extremely at the end,because most of the RAM was used.lossed on lot of
memory.
When you accessed too much of data,the address you get is
different.
To access a storage location in RAM,going by a
address is a principle that works only on microprocessors.
(this works here in
8086 and 8051 microprocessor,because you know the addresses).
But here it is dynamic addresses.
What every programming language comes up is,it will define
something called as variable.
So the purpose of variable is to give,an alias to your
memory location.because for me it is difficult right,
For example on my machine,this is the address xof334f
On your machine,something it is like 0xfgc …
(this is not same and even if I execute again,I don’t know I
get the same addresses).
Every programming language,as a concept of referring to the
address in your memory,that is been done with the concept of variable.
For example:
If I write sometime like
a=10;
(your intension,to store the value called 10 in to the RAM).
When you store 10 in to the RAM,you get the address.
And from there,you define the address not from there,but you
will give the alias name as ‘a’.
For example
à a =a+1
(what your saying access a=10 and perform addition on that).
(11,assign this to the address,where it was present).
Basically,we are operating on memory.
Note:
Variable is nothing
but a reference to a memory location.
(it looks readable
and simple,in everyone’s machine).
(One thing is clear
that,we are allocating the memory right and we refer that by variables).
Next question:
how much memory we
have to allocate?
We cannot have integers throughout our program.
We use,many kinds of data.
The size of the data,is determined by what your storing.
That is,why
programming languages will have a
concept called the datatypes:
The primary reason
for datatypes is:
To tell your operating system,how much memory,do you need on
RAM.
For example:
Integer is a 32 bit.
Boolean(true/false) -à
1bit
Floating numbers.
Realnumbers.
Decimal points also.
Whenever you write something like int a.
Basically,your demanding 32 bit of space in the RAM.
So,we are having different kinds of data.
Note:
All of these
called,fixed lenght of datatypes.
But there are,majority of the data,what we used are not
fixed:
Example:
Using ruby,we are all writing library application,will every
book will have a name with same characters.every book title will have same
length?,similarly every book’s authors name,there are many factors,when you text,you
cannot fix.
So that’s way,they defined a variable called the `string`.
Note:
Whenever your
referring a string,your referring as,variable length datatype.
You will not be able
to determine the size of the string,until you assign a value.
For EXAMPLE:
WORKING NATURE OF
STRING:
String a = “hello”
So it requires the space of 5+1, 6 characters.
For each character,how much space it takes?
These calculations happened dynamically.
In simple,
How many kinds of
datatypes?
Fixed-length (integer,Boolean……etc),there
will be a number assigned to it and it is easy for the programming language to
ask for it).
Variable-length.
-à a = a.append(“hai”)
basically,I want to write hello hai
(initially,it requires 6 spaces and suddenly your asking same
variable,where it size was gone from
to appx 8 characters.
For example,each character is a byte,that means 6 now
demands 9 to 10 spaces.
Whenever you do operations on memory,you do that.
For example,
The above box is system allocation.
The first statement,you executed is a. it is 6 characters.
That is hello, --à you the space as `OUR` in figure
After that someone has space à
it is `Some`.
Now,your requirement
was changed from 6 characters to 9
(can you allocate
over there,I mean can you allocate sequentially,because your characters have to
be sequential,whenever you execute).
Now,what is the
problem,with that?
Whnever you use a string everytime,what happens generally
is,everytime a new memory will be allocated.
Whenever you change any change anything on the string.
Let it be increasing or let be decreasing.
That’s why strings are called as immutable datatypes.
Note:
Whatever,you operate,everytime a new memory will be
allocated.
(you have to be careful with the string,with this
understanding).
There will be multiple applications,who are requesting for
the RAM,the chrome browser which requires some memory,you launched word
application,you launched excel application they will also require some memory
right.
For example:
After your programming task is finished,somebody might be
asking for the memory.
(and you cannot guarantee,always the sequential amount of
characters).
Working with the
variable datatypes:
Generally,there are immutable because,especially when there
are growing or decreasing.loss on certain spaces.
Note:
We cannot have fixed spaces in any programming languages.
Note:
Strings are called as
immutable datatypes,
example:
whatever operation
you do on the string.
à a = a.append
à
a = a.remove (if you done,something,to
remove one character).
(these kind of operations ,your allocating a new memory
everytime).
Note:
So,whenever your working on string,be careful.
Note:
So,we have to write,these kind of operations in the `FOR loop`.
Note:
For example:
You cannot write
`while (true)`
a= a+1
where a is string,your application(programming) will be
crashing.
(because,your application is continuously increasing the
memory).
Then after the sometime,you get an error,how is your machine
is and a prompt running out of memory.
(Strings are always,variable-length).
Note:
While learning any programming language,the first thing,we
have to focus on what datatypes are available and how to apply.
And once you,know that,its just applying the syntaxies.
What are the
variableS that are supported in Ruby?
Fortunately,you noneed to be explicit about your datatypes in the ruby language.
For example: if write the code,
a =10 (there is no need tell that is an integer,ruby will
understand automatically).
a = 10.3 (in this
case,it will identify,being a float).
a = “hello”
(a can be only one datatype,)
I want to store one package name,if you have a variable,I
can store the package name.
Rather than,having “a” I will be writing:
Package_name=”httpd”
(this is what,we have to prefer).
Version_number=7.9
Or
We can give “7.9”
Version_number=”7.9”
(if you give 7.9 in quotes,is it a string or a number,it is
a string).
If it either ‘ ‘ or “
“ it is a string,with out quotes (Double/single) then it is a number.
Ruby datatypes
1)Strings
2)Numbers
3)Arrays
4)Hashes
5)Symbols.
We will be using
symbols a lot.
à action
:install (: the semicolon is
called the symbol here).
what is a ruby symbol
?
whenever you see the string,starting with the symbol that is called the ruby symbol.
(they have effective way of managing strings and symbols).
We can write in two ways,it gives the same result.
àaction
:install
àaction
“install”
(symbol is a better
way of handling,that’s what ruby believe).
The example are from irb (interactive ruby).
Irb<main>:008:0= :
Trying variables in
powershell
Irb<main>:008:0> no_of_installation=10
= > 10
Irb<main>:008:0> no_of_installation
= > 10
Irb<main>:008:0> no_of_installation=100
= > 100
(it gave me 100).
Irb<main>:008:0> package_name= “apache2”
= > “apache2”
Irb<main>:008:0> package_name= “httpd”
= > “httpd”
Irb<main>:008:0> package_name
= > “httpd”
(because that was the last executed state).
Lets us assume that,I have variable name as package_name
right.
I want to print which looks something like this:
I am going to install,(whatever name is there in the package
file) -à
apache2.
Note:
With in a string,you want to use a string,but that string
should not be hardcoded,you want to use it dynamically.
“I am going to install apache2 and count = your number of installations”.
Actually,you want to write a string which is dynamically
now.
I am not to install,whatever the variable name and count
=10.
(you have two variables and we are trying to create a
string,try to accomidate values of two variables).
This kind of things
are called as formatting/code substitutions.
Techincal term for
this process = interpolation.
How to do this in
ruby?
There is a standard syntax,which you need to follow:
(whenever your do
this code substitution/interpolation your strings cannot be in single quotes).
Note
Your string has to be
in double quotes.
Difference between
single quote strings and double quote strings in ruby
single quote strings
-à if your string is single quote,you cannot
interpole it.
(or you cannot substitute the values of other variables in
to this).
So for any kind of
substitution,we will use the double quotes.
Irb<main>:008:0> message = “I am going to install #{package_name}”
(In most of our configuration files right,we have to change
certain values).
This is something,we will be using a lot.
Irb<main>:008:0> message = “I am going to install #{package_name} and count =
(no_of_installations) [(another variable) that is
interpolation/substitution].
“I am going to install
httpd and count =100”
Note:
The syntax for the
code substitution is :
#{<variable_name>}
we need to use
this,in our strings,so that value of that string substituted.
One more explanation on that:
Sometimes,the data
which you want to access,might not be singular.
For example,you want
to install three installations.
You need to give the data,multiple in nature.
In this situation,we will be using the Array.
Basically,Array multiple data that has been present.
(I want to have multiple values in a variable)
because I want to install,multiple installations.
We would like to create a variable called
package_name
Irb<main>:008:0> package_name =
[“apache2”,”wget”,”tree”]
(these are the sofwares to be installed).
= > [“apache2”,”wget”,”tree”] (this is the output).
The first item we are giving is apache2 and the next item,we
want to give is the indexing.
[index is the postion
of item in the string].
Whenever the position,the array index,starts at zero.
We have to always
reduce the [postion-1].
First position is
apache.
Second position is wget.
Third position is tree.
“arrays index starts
from zero”
Irb<main>:008:0> package_names[0]
= = > “apache2”
Irb<main>:008:0> package_names[2]
= = > “tree”
Irb<main>:008:0> package_names[4]
= = > nil
(In array,we will
have,all the things with the datatype).
This is my arrays variable name packages_and_versions =
[“apache2”,”1.7”,”tomcat”,9].
We have a combination
of string and other datatypes.
Irb<main>:008:0> [“apache2”,”1.7”,”tomcat”,9].
= >
[“apache2”,”1.7”,”tomcat”,9].
(this is allowed).
Note: An array in
ruby,need not to be same datatype.can be of multiple datatypes.
In ‘C’ language
it is homogenous kind of datatype.(that means same datatype in an array).
But that is not the
case in ruby.
That is not the
case,even in python.
In ruby,
It is just collection of data.(it Is irrespective of
datatype).
How to implement all
the above things in to the recipe?
For example the below
one is the recipe:
#cookbook
#Recipe:: tomcat_install
apt_update ‘update
ubuntu’ do
action
:update
end
package ‘tomcat7’
do
action
:install
end
service ‘tomcat7’ do
action
:start
end
Note:
We are using the ‘tomcat7’ for several times,this creates
memory allocations in many places.
(even the value is same,we are creating two memory
locations).
Rather than,using this,create a variable.
Tomcat_pack_name = tomcat7
apt_update ‘update
ubuntu’ do
action
:update
end
package ‘Tomcat_pack_name’ do
action
:install
end
service ‘Tomcat_pack_name’
do
action
:start
end
now,we are having tomcat7 at one memory allocation,we are
saving some memory in the programming.
Whenever your seeing repetition of values,rather than
hardcoding them,putting them in the variable makes more sense.
(it just reads the variable value).
(These are dynamic languages,assign the value).
(it will indentify the value,which it wants to).
Arrays:
If you don’t want to
write in the square bracket syntax,you can also write:
%w (we can write it
by using the %w).
and write three of
the variables with spaces.
Note:
Whenever your seeing %w that means,he is giving,array
representation of w.
I want to define,details about this package:
Note:
Everytime,you do the irb,your past variables,will not exist
anymore.
Irb<main>:008:0>
package_ports = [“apache2”,8080, “tomcat”,8081,
“tree”, “wget”]
(for simplicity of that,we are writing two entries).
“” means those are the strings.
You have to write the program,which will identify the port
number of the apache2.
The logic is the:
The postion of our packages
name +1.
The problem with
this,kind of approach is your assuming conditions.
When you write only the package names in the Array
structure,that is the perfect approach.
When you try to mix
and match the structure,Array is not meant for
that:
Irb<main>:008:0>
package_ports = [“apache2”,8080, “tomcat”,8081,
“tree”, “wget”]
(for simplicity of that,we are writing two entries).
Array is not mean for
the above staructure.
Array means
collection of same to you.
It may not be same
datatype.
Probably you want to write student names.
If you want to tell
more than one thing in the structure:
(hash(= >) --à is the key value pair.
(hash(= >) -à start with the { (curl braces) and ends with
the } (curl braces).
And then you would
have a,
{
key = > [(this is the ruby hash) then we have the] value
key1 = > value1
key2 = > value2
key3 = > value3
.
.
}
This is the syntax.
If you want to say
about the employee
{
emp.id => 1234
name => Kaushik
postion => [“DevOps”
, “AWS”, “Bamboo”,”Docker”]
}
I want to write the
details of multiple employees.
(whenever I say it is multiple,it is an array).
[{
emp.id => 1234
name => Kaushik
postion => [“DevOps”
, “AWS”, “Bamboo”,”Docker”]
}
{
emp.id => 1235
name => John
postion => [“DevOps”
, “AWS”, “Bamboo”,”Docker”]
}
{
emp.id => 1235
name => ricky
}
(now ricky,does not have a postion,then ricky will get a
nil/null position).
Example for the
employee,using the variable and the key,value structure:
Irb<main>:008:0>
employee = [ “emp.id” => 1234, “name” => Kaushik ,
“postion” => [“DevOps” , “AWS”, “Bamboo”,”Docker”]
Irb<main>:008:0>
employee [emp.id]
1234
Irb<main>:008:0>
employee [name]
Kaushik
Whenever,you want to describe about the item,if your trying
to describe more than one item,then we will go for the hashes.
We uses the (hashes) in our programming language.
Note:
An hash can contain
an array and also array can contain a hash.
We use ruby hashes (
= > )a lot.
Especially,when we discuss the attributes.
Once,we know,how to write conditions,we discuss about the
attributes.
Describe,about some package,when we need to include multiple
things.
Array can be multiple items
(An item can be string,Boolean,…).
In hash,
We have a key and value.
Note:
The value of the
hash,can be another hash also.
(this is also
possible,if your describing about,more complicated).
Example:
If you want to include the address of the employee.
{
emp.id => 1235
name => John
postion => [“DevOps”
, “AWS”, “Bamboo”,”Docker”]
Address = > {
“Firstlane”
=> “”,
“city” => “”,
“state” => “”,
}
(the address can be hash also,it can be any datatype.(integer
is one way of representing data,array is one way of representing the data)).
what is the property
of any hash? => it should have a key and value.
Note:
A value of a hash can be other hash also.
How to test the hash?
Go to your powershell and
Ø
Facter
Then you will get all the details of the system in the
values of the hash (that is the key and value pair).
For example:
I want the
system_uptime (this is the key of the
hash).
>>>>>> facter system_uptime
{
days => 0,
hours => 1,
seconds => 6291,
uptime => “1.44 hours”
whenever you want to use this syntax in the programming
language,you have to use this syntax:
>>>>>> facter[“system_uptime”]
{
days => 0,
hours => 1,
seconds => 6291,
uptime => “1.44 hours”
}
if you want to this,in your recipe for some reason.(the
above syntax,should be followed).
>>>>>>
facts[“system_uptime”][“days”]
that is stored in to a variable called facts.
Note:
When we type the
facter we get all the information related
to the system and that is stored in a variable called the “facts”.
And after that we are using the hashes syntax
to find anything.
Note:
When we type the
facter in the linux machine,we get the complete information,related to the
machines and this information,we use in our recipes,to add more dynamic nature
to the code,this is the use of the hashes.
Example of ,how to
use the hash and facts in the chef-recipe:
#cookbook
#Recipe:: tomcat_install
facts[“os”][“name”]
apt_update ‘update
ubuntu’ do
action
:update
end
package ‘tomcat7’
do
action
:install
end
service ‘tomcat7’ do
action
:start
end
Note:
We have two recipes
and it has same variables,inside the recipes?
In this specific scenario,two recipes will be executing two
different memory spaces,so there is no need to worry about this.
Example:
It is like,two programs
having same variables.
