DevOps Classroom Series – 07/Aug/2020

Inventory Parsing

• Inventory is basic building block of Ansible architecture
• when we execute ansible or ansible-playbook an inventory must be referenced.
• Location of inventory can be referenced with -i or –inventory-file argument or ansible will pick up inventory from the path defined in ansible.cfg (/etc/ansible/ansible.cfg)
• Inventories can be static or dynamic.
• In enterprise we have different inventory files for different environments like
  • QA
  • Staging
  • Dev
  • Production

ansible-playbook -i staging/hosts deploy-app-service.yaml

ansible-playbook -i qa/hosts deploy-app-service.yaml

ansible-playbook -i dev/hosts deploy-app-service.yaml

ansible-playbook -i production/hosts deploy-app-service.yaml

Static Inventory

• Static inventory has a static list of hosts (defined by hostnames or ip addresses) in an ini format in file.
• The following are some of the inventory types which we have used
  • inventory with only host names

  localhost
  

  • inventory with group names and hosts under groups

[centos]
172.31.4.122 

[ubuntu]
172.31.3.192 

* inventory with group names and groups with children and

[centos]
172.31.4.122 

[ubuntu]
172.31.3.192 

[webserver:children]
centos
ubuntu

Inventory ordering

• A Play level keyword, order was added in Ansible, which can have following values
  • inventory: This is default option & it means the hosts will be processed as written in inventory file
  • reverse_inventory: The hosts will be processed in the reverse order to what is specified in inventory
  • sorted: The hosts will be processed in alphabetically sorted order name
  • reverse_sorted: The hosts will be processed in reverse alphabetically sorted order name
  • shuffle: The hosts will be processed in a random order
• Lets create an inventory

localhost
172.31.4.122 
172.31.3.192 

• Lets create a playbook

---
- name: testing order
  hosts: all
  tasks:
    - name: ping the host
      ping:

• Now lets change the order

---
- name: testing order
  hosts: all
  order: sorted
  tasks:
    - name: ping the host
      ping:

• To test this try executing commands with this

ansible-playbook -f 1 -i trailinventory ping.yaml

Inventory variable data

• Inventories provide more than just system names and groupings. Data necessary for groups and hosts also can be passed along. The data may include
  • Host specific data
  • Group Specific data
  • Behavioral parameters to tune how Ansible interacts
• Lets create an inventory

localhost   package_name="test"
172.31.4.122 package_name="testing"
172.31.3.192 package_name="not testing"

• Lets create a playbook with a module called as debug Refer Here

---
- name: testing variables
  hosts: all
  tasks:
    - name: print the variable
      debug:
        var: package_name

• Now lets execute the playbook
• Now lets introduce groups and group variables

[local]
localhost

[centos]
172.31.4.122
localhost

[ubuntu]
172.31.3.192

[webserver]
172.31.3.192
172.31.4.122

[all:vars]
package_name="from all"

• Now execute playbook
• Now lets change inventory as shown below & re-execute

[local]
localhost

[local:vars]
package_name="from local"

[centos]
172.31.4.122
localhost

[centos:vars]
package_name="from centos"

[ubuntu]
172.31.3.192

[ubuntu:vars]
package_name="from ubuntu"

[webserver]
172.31.3.192
172.31.4.122

[webserver:vars]
package_name="from webserver"

[all:vars]
package_name="from all"

• Now lets change the inventory as shown below & execute

[local]
localhost package_name="localhost"

[local:vars]
package_name="from local"

[centos]
172.31.4.122 package_name="172.31.4.122"
localhost

[centos:vars]
package_name="from centos"

[ubuntu]
172.31.3.192 package_name="172.31.3.192"

[ubuntu:vars]
package_name="from ubuntu"

[webserver]
172.31.3.192
172.31.4.122

[webserver:vars]
package_name="from webserver"

[all:vars]
package_name="from all"

• Now lets execute the following command

ansible-playbook -i inv4 -e "package_name=extravars" playbook1.yaml

• In ansible when we run playbooks & if the same variable is defined at multiple, ansible has some kind of priority system which we will be learning "Ansible variable precedence"

Next steps

• Understanding Behavioral parameters
• Variable files
• Dynamic inventories
• Playbook parsing & ordering