[PPT] - Ansible in Operatjon Bruce Becker: Coordinator, SAGrid

SLIDE 1

Bruce Becker: Coordinator, SAGrid | bbecker@csir.co.za | http://www.sagrid.ac.za

Ansible in Operatjon

SLIDE 2

Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 2

Learning Goals

Manage inventory
Ansible ad-hoc commands
Write & run Playbooks
Understanding of variables
Loops and conditjons

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 3

Inventories

A list of hosts, groups and aspects of hosts
Can be dynamic or statjc
Groups defjned by brackets [

] and by name

Describe systems
Decide what systems you are controlling at what tjmes and for what

purpose (roles)

Groups can be nested with :

c h i l d r e n

Hosts can be in more than one group
server could be both a webserver and a dbserver.
variables will come from all of the groups they are a member of

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 4

Statjc Inventories

Statjc inventory : simplest, most common form
Add a group
Add host variables

l

c

a l h

s

t l

c

a l h

s

t [ C e n t O S ] l

c

a l h

s

t L

c

a l h

s

t a n s i b l e _ s s h _ h

s

t = 1 2 7 . . . 1 [ C e n t O S ] l

c

a l h

s

t

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 5

Dynamic Inventories

Statjc inventories negate the environment of the

cloud

Can use almost data source to generate dynamic

inventories

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 6

Lesson 1: Run an empty play

1. g

i t i n i t

2. Confjgure an inventory fjle
3. Create at least one group (by OS)
4. Start a playbook
5. Run the empty playbook against all hosts

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 7

Host selectjon

Host selectjon can be done by incuding or excluding

groups and single hosts

Selectjon can be done by passing :
a

l l / *

Groups names
Exclusion (a

l l : ! C e n t O S )

Intersectjon (w

e b s e r v e r s : & s t a g i n g )

Regex

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 8

Executjng - Tasks

Ad-Hoc: commands which execute single tasks
Tasks: leverage an Ansible module, which is

executed on the target host

Modules:
(Mostly) writuen in Python
Shipped via SSH to the target host
Return JSON, interpreted by Ansible for outcome
Removed once executed

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 9

Executjng - Modules

Modules are the ”Batueries included” of Ansible
Core modules provided by Ansible and ”extras”

by the community

Well-documented
Web :

htup:/ /docs.ansible.com/ansible/modules_by_category .html

CLI : a

n s i b l e

d
c
l

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 10

Hands-on session Ansible ad-hoc commands

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 11

Ad-hoc actjons

1. Check facts on all hosts

1 . A n s i b l e a l l

i

i n v e n t

r

y

m

s e t u p

2. Copy a fjle
3. Install nginx and add a user
4. Clone a git repo to a path
5. Ensure that htupd is present and started
6. Background operatjons, with polling

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 12

Orchestratjon

The true power of ansible comes from

abstractjon and orchestratjon, using playbooks

Playbook is a set of ordered tasks, combined with

selected targets

Playbooks provide ready-made strategies for

bringing (groups of) hosts to a desired state

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 13

Roles

Roles provide a way to encapsulate and re-use

code

Instead of writjng lots of tasks, your playbook can

be more readable and understandable to someone else :

h
s

t s : d i r a c u s e r : a n s i b l e s u d

:

t r u e r

l

e s :

b
t

s t r a p

c
m

m

n
c

e r t i f i c a t e s

d

i r a c

Roles are applied in order Roles may have dependencies

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 14

Roles and fjlesystem structure

s i t e . y m l r

l

e s / r

l

e 1 / f i l e s / t e m p l a t e s / t a s k s / h a n d l e r s / v a r s / m e t a /

Roles are usually

placed in a ”library” in a sub-directory.

Each role has a

standard structure

Roles can be

scafgolded using a n s i b l e

g

a l a x y

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 15

Creatjng new roles with Galaxy

A new role can be created using

a n s i b l e

g

a l a x y i n i t < r

l

e n a m e >

Ensure that you create the role in the ”roles” directory,
r you won't be able to simply call them by name in the

playbooks.

Ansible Galaxy creates all the fjles you need to get

started, including a README and a meta fjle

Roles can be shared and discovered via

htup:/ /galaxy.ansible.com

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 16

Variables

While automatjon exists to make it easier to make things

repeatable, all of your systems are likely not exactly alike.

The behaviour or state of confjgured machines may change

and impact the desired state of other services, dynamically

Certain confjguratjon fjles may exist as templates, which

need instantjatjon, based on their context

Variables in Ansible are how we deal with difgerences

between systems and states

Variables allow you to ”program” with conditj

tjons and loops

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 17

Settjng Variables

Variables in Ansible help you to contextualise and

abstract roles.

Variables can be defjned in several areas
Inventory
Playbook
Files and Roles
Command Line
Facts

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 18

Variable Hierarchy

1) Command line variables have the highest precedence. - e 2) 'most everything else' come next.

1)Role vars 2)Task and play variables

3) Variables defjned in inventory.

1)Host and group vars

4) Next comes facts discovered about a system. 5) Default vars defjned in roles have the lowest priority

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 19

Host Variables

Host variables are assigned in the inventory
Arbitrary variables can be assigned to individual

hosts

There are also variables which change the way

Ansible behaves when managing hosts e.g

http://docs.ansible.com/ansible/intro_inventory.html#host-variables

9 . 1 4 7 . 1 5 6 . 1 7 5 \ a n s i b l e _ s s h _ p r i v a t e _ k e y _ f i l e = ~ / . s s h / a n s i b l e

d

e f a u l t . k e y \ a n s i b l e _ s s h _ u s e r = c e n t

s

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 20

Group Variables

Hosts are grouped according to aspects, or any desired

grouping

Ansible allows you to defjne group variables which are

available for any host in a group

Group variables can be defjned in the inventory:

[ w e b s e r v e r s : v a r s ] h t t p _ p

r

t = 8

Or in separate fjles under group_vars

g r

u

p _ v a r s / w e b s e r v e r s →

h

t t p _ p

r

t = 8

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 21

Facts

Facts are discovered about the play hosts at the start
f each play
Unless turned ofg with g

a t h e r _ f a c t s = f a l s e

Facts can be cached
Facts uses the setup module, which uses various tools

such as f a c t e r and o h a i to obtain facts about hosts

Facts are useful in determining the state of the

machines in the play

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 22

Registering and using variables

Variables can be statjcly set in the inventory,

roles or plays, but can also be picked up based on the events of the play

Use register to set transient variables

r e g i s t e r : n e w v a r

Call variables using {

{ n e w v a r } }

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 23

Example – Ensure that EPEL is available only on RedHat machines

Vars set in role/x/vars:
e

p e l _ p a c k a g e : ' 6 ' : h t t p : / / f t p . f a u . d e / e p e l / 6 / x 8 6 _ 6 4 / e p e l

r

e l e a s e

6
8

. n

a

r c h . r p m ' 7 ' : h t t p s : / / f t p . f a u . d e / e p e l / 7 / x 8 6 _ 6 4 / e / e p e l

r

e l e a s e

7
5

. n

a

r c h . r p m b a s e _ p a c k a g e s :

h

t t p d

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 24

Example – Ensure that EPEL is available only on RedHat machines

Use the facts and role variables in a task
a

n s i b l e _ d i s t r i b u t i

n

_ m a j

r

_ v e r s i

n

: discovered fact

e

p e l _ p a c k a g e : role variable

e

p e l i n s t a l l : registered variable

n

a m e : E n s u r e t h a t E P E L i s p r e s e n t a n d c

n

f i g u r e y u m : n a m e : " { { e p e l _ p a c k a g e [ a n s i b l e _ d i s t r i b u t i

n

_ m a j

r

_ v e r s i

n

] } } " s t a t e : p r e s e n t r e g i s t e r : e p e l i n s t a l l

n

a m e : R e

g

e n e r a t e m e t a d a t a y u m : n a m e : ' * ' s t a t e : l a t e s t w h e n : e p e l i n s t a l l . c h a n g e d

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 25

Magic Variables

Some variables are automatjcally created and

fjlled by Ansible :

i

n v e n t

r

y _ d i r

i

n v e n t

r

y _ h

s

t n a m e

i

n v e n t

r

y _ h

s

t n a m e _ s h

r

t

i

n v e n t

r

y _ f i l e

p

l a y b

k

_ d i r

p

l a y _ h

s

t s

h
s

t v a r s

g

r

u

p s

g

r

u

p _ n a m e s

a

n s i b l e _ s s h _ u s e r

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 26

Variable from a n s i b l e _ f a c t s

" a n s i b l e _ f a c t s " : { " a n s i b l e _ a l l _ i p v 4 _ a d d r e s s e s " : [ " 1 9 2 . 1 6 8 . 2 . 2 2 " , " 1 7 2 . 1 7 . 4 2 . 1 " ] , " a n s i b l e _ d e f a u l t _ i p v 4 " : { " a d d r e s s " : " 1 9 2 . 1 6 8 . 2 . 2 2 " , " a l i a s " : " w l a n " , " g a t e w a y " : " 1 9 2 . 1 6 8 . 2 . 1 " , " i n t e r f a c e " : " w l a n " , " m a c a d d r e s s " : " 3 c : a 9 : f 4 : d : 7 4 : c 8 " , " m t u " : 1 5 , " n e t m a s k " : " 2 5 5 . 2 5 5 . 2 5 5 . " , " n e t w

r

k " : " 1 9 2 . 1 6 8 . 2 . " , " t y p e " : " e t h e r " } } ,

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 27

Calling complex variables

Ansible uses mostly JSON to manage variables.
Variables can have arbitrary complexity.
Variables can be dereferenced using two

difgerent syntaxes :

{

{ a n s i b l e _ e t h [ " i p v 4 " ] [ " a d d r e s s " ] } }

{

{ a n s i b l e _ e t h . i p v 4 . a d d r e s s } }

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 28

Conditjons

Ansible provides a means to apply boolean or other conditjons on

variables

Usually used in tasks or templates with the Jinja w

h e n statement – e.g.

n

a m e : " s h u t d

w

n D e b i a n f l a v

r

e d s y s t e m s " c

m

m a n d : / s b i n / s h u t d

w

n

t

n

w

w h e n : a n s i b l e _

s

_ f a m i l y = = " D e b i a n "

Use parentheses () to group conditjons:

w h e n : a n s i b l e _ d i s t r i b u t i

n

= = " C e n t O S " a n d ( a n s i b l e _ d i s t r i b u t i

n

_ m a j

r

_ v e r s i

n

= = " 6 "

r

a n s i b l e _ d i s t r i b u t i

n

_ m a j

r

_ v e r s i

n

= = " 7 " )

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 29

Loops

Ansible loops are useful for writjng cleaner

playbooks and templates.

Ansible provides several ways to loop:
Standard Loops
Nested Loops
Looping over Hashes
Looping over Fileglobs
Looping over Parallel Sets of

Data

Looping over Subelements
Looping over Integer Sequences
Random Choices
Do-Untjl Loops
Finding First Matched Files
Iteratjng Over The Results of a

Program Executjon

http://docs.ansible.com/ansible/playbooks_loops.html

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 30

Example: Loops in templates

An easy way to generate an /

e t c / h

s

t s fjle { % f

r

h

s

t i n g r

u

p s [ ' h e a d

n
d

e s ' ] % } { { h

s

t v a r s [ h

s

t ] [ ' a n s i b l e _ e t h ' ] [ ' i p v 4 ' ] [ ' a d d r e s s ' ] } } { { h

s

t } } { % e n d f

r

% }

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 31

Example: Loop over a list

A list variable can be used in a task to perform

several similar actjons using the same module:

n

a m e : I n s t a l l b a s e p a c k a g e s y u m : n a m e : " { { i t e m } } " s t a t e : p r e s e n t w i t h _ i t e m s :

t

h i s _ p a c k a g e

t

h a t p a c a k g e

a

n

t

h e r p a c k a g e

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Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 32

Recap

We have writuen our fjrst inventory and started to manage
ur machines with Ansible
Ad-hoc commands are once-ofg ways to perform tasks on

sets of hosts

Playbooks are more complex groupings of tasks which

defjne the desired states of our managed hosts

Playbooks depend on variables, which have a hierarchical

precedence and allow proper contextualisatjon of the tasks

Ansible has the powerful feature of variables, including the

possibility to have conditjonal statements and loops.

SLIDE 33

Bruce Becker: Coordinator, Africa-Arabia ROC | bbecker@csir.co.za 33