Ansible – Part 4 – Managing Inventory

Inventory File

An inventory file is a simple and plain text file where we store those host information ansible has to deal with. It can be simple in any format (YAML, ini, etc). Default inventory file location is /etc/ansible/hosts but you can specify a different inventory file in your ansible config file (as above) or using the -i option on the command line.

[[email protected] ~]# ansible all -m ping -i myinventory

Here see a sample inventory file.

[myself]
localhost

[intranetweb]
servera.techbeatly.com
serverb.techbeatly.com

[database]
db101.techbeatly.com

[everyone:children]
myself
intranetweb
database

You can see, this is a simple one in ini format and contains few hosts and groups. Group myself contains only one host which is localhost. (Not a mandatory one, I have given as an example). intranetweb group containers 2 servers – servera.techbeatly.com and serverb.techbeatly.com. db101.techbeatly.com is under database group. And finally we have group everyone with all other groups as children.

Lets check what ansible can understand from this inventory file.

[[email protected] ansible]# ansible all --list-hosts
  hosts (4):
    db101.techbeatly.com
    localhost
    servera.techbeatly.com
    serverb.techbeatly.com
    
[[email protected] ansible]# ansible intranetweb --list-hosts
  hosts (2):
    servera.techbeatly.com
    serverb.techbeatly.com    

Here see some of the sample ansible --list-host pattern for reference.

ansible db1.example.com -i inventory --list-hosts
ansible -i inventory --list-hosts 172.25.252.44
ansible -i inventory --list-hosts all
ansible -i inventory --list-hosts london
ansible -i inventory --list-hosts environments
ansible -i inventory --list-hosts ungrouped
ansible -i inventory --list-hosts '.example.com'
ansible -i inventory --list-hosts '.example.com,!.lab.example.com'
ansible -i inventory --list-hosts lb1.lab.example.com,s1.lab.example.com,db1.example.com
ansible -i inventory --list-hosts '172.25.'
ansible -i inventory --list-hosts 's'
ansible -i inventory --list-hosts 'prod,172,lab'
ansible -i inventory --list-hosts 'db,&london'

If you are adding a lot of hosts following similar patterns, you can add as below rather than listing each hostname:

[webservers]
www[01:50].example.com
[databases]
db-[a:f].example.com

192.168.0.[10:20]
[a:c].dns.example.com

Dynamic Inventory

Inventory can be static (like ini or YAML format) or dynamic via inventory scripts. For those working on cloud or container based environment, you will not be able to manage inventory with a static source. In that case you need a dynamic inventory system with scripts.

There are few sample inventory scripts available by community; check this repo for samples : https://github.com/ansible/ansible/tree/devel/contrib/inventory

[[email protected] dep-dynamic]$ inventory/myinventory.py --list
{"webservers": {"hosts": ["servera.teachbeatly.com"], "vars": {}}}

Let’s learn about ad-hoc commands in next chapter.

See all parts of  Automation with Ansible Guides here

Gini Gangadharan

Gineesh Madapparambath | Backpacker, Foodie, Techie | techbeatly.com|rovervibes.com

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