Inventories

Inventories are a fundamental doc entrypoint for our infrastructures.

They contain a lot of informations, including:

- ansible_user
- configuration variables in [group_name:vars]
- host grouping eg. by geographical zones in [group_name:children]

Files:

inventory



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cd /notebooks/exercise-05



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!cat inventory

The ansible executable can process inventory files



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!ansible -i inventory --list-host all

Exercise

Use ansible to show:

- all hosts of the web group.



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# Use this  cell for the exercise



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# The ping module is very useful. 
# Use it whenever you want to check connectivity!
!ansible -m ping -i inventory web_rome

Inventory scripts



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#To create custom inventory scripts just use python ;) and set it in
!grep inventory  ansible.cfg # inventory = ./docker-inventory.py

Exercise

in the official ansible documentation find at least 3 ansible_connection=docker parameters



In [ ]:

    
"""List our containers. 

  Note: this only works with docker-compose containers.

"""
from __future__ import print_function
# 
# Manage different docker libraries
#
try:
    from docker import Client
except ImportError:
    from docker import APIClient as Client


c = Client(base_url="http://172.17.0.1:2375")

# Define a function to make it clear!
container_fmt = lambda x: (
    x['Names'][0][1:],
    x['Labels']['com.docker.compose.service'], 
    x['NetworkSettings']['Networks']['bridge']['IPAddress'],
)

for x in c.containers():
    try:
        print(*container_fmt(x), sep='\t\t')
    except KeyError:
        # skip non-docker-compose containers
        pass



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# Ansible accepts
import json

inventories = {
    'web': {
        'hosts': ['ws-1', 'ws-2'],
    },
    'db': {
        'hosts': ['db-1', 'db-2'],
    }
}

# like this 
print(json.dumps(inventories, indent=1))



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# You can pass variables to generated inventories too
inventories['web']['host_vars'] = {
    'ansible_ssh_common_args': ' -o GSSApiAuthentication=no'
}
print(json.dumps(inventories, indent=1))

Exercise:

Reuse the code in inventory-docker.py to print a json inventory that:

connects via docker to "web" hosts
connects via ssh to "ansible" hosts

Test it in the cell below.

NOTE: there's a docker inventory script shipped with ansible



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!ansible -m ping -i inventory-docker-solution.py all

Exercise

Modify the inventory-docker.py to skip StrictHostKeyChecking only on web hosts.



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# Test here your inventory

Configurations

You may want to split inventory files and separate prod and test environment.

Exercise:

split inventory in two inventory files:

prod for production servers
test for test servers

Then use ansible -i to explicitly use the different ones.



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# Use this cell to test the exercise

group_vars and host_vars

You can move variables out of inventories - eg to simplify inventory scripts - and store them in files:

under group_vars for host groups
under host_vars for single hosts



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!tree group_vars

If you have different inventories, you can store different set of variable in custom files. The all ones will be shared between all inventories

Exercise:

edit group_vars/all and move there all common variables from inventory



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# Test here the new inventory file

Inventory variables can store almost everything and even describe the architecture of your deployment



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!cat group_vars/example

We can even mix and mojo group_vars and inventory, as we'll see in the next lessons.

host_vars

Host vars can be used in automated or cloud deployments where:

every new host or vm, at boot, populate its own entries in host_vars (Eg. via file)
ansible is run after that setup and uses host_vars to configure the server and expose that values to the other machines.