3.0 - Ansible Inventory¶

03.1 - Ansible Inventory¶

Introduction¶

Ansible can work with one or multiple systems in the system at the same time
This requires it to establish connection via SSH (Linux) or Powershell Remoting (Windows)
This makes Ansible agentless - no additional packages are required for connection to be established to the target machines, unlike similar tools.
Information regarding the target machines is noted in an Inventory file, stored by default in /etc/ansible/hosts , an example follows:
Servers can be listed one after another as standalone entries or as part of a group, denoted by [groupname]
Aliases for hosts, for ease of reference, can be added in a manner similar to:

<alias> ansible_host=server.company.com

Other parameters are available for use in inventory files, such as:
ansible_connection - ssh/winrm/localhost
- Determines how ansible connects to the target server - Linux or Windows-based system, or applying changes to localhost
ansible_port - 22/5896
- 22 for SSH by default
ansible_user - root/administrator
- User logging in to make changes, set to root by default
ansible_ssh_pass - Password
- ssh password for linux - NOT RECOMMENDED to do this in plaintext, ssh key-based passwordless authentication should be used, especially in production environments.

03.2 - Demo: Ansible Inventory¶

Introduction¶

Verify connection between ansible-controller and targets 1-2 via ssh
Create an inventory.txt file and add details regarding ansible-target1 in a format similar to:

<hostname> ansible_host=<IP> ansible_ssh_pass=<password>

Once complete, run the following command:

ansible target1 -m ping -i inventory.txt

This calls ansible to use the ping module to test the connection to the host target1 based on the inventory file inventory.txt's information.
A successful message will be similar to:

ansible-target1 | SUCCESS => {
    "ansible_facts": {
        "discovered_interpreter_python": "/usr/bin/python"
    },
    "changed": false,
    "ping": "pong"
}

Repeat for the second target machine.
Note, if SSH has not been successful for any of the target machines, this will fail.
Alternatively, changes can be made to the /etc/ansible/ansible.cfg by uncommenting the line that asks "host key check

Exercises¶

We have a sample inventory file with 3 servers listed. Add a fourth server by the name server4.company.com.

## Sample Inventory File

server1.company.com
server2.company.com
server3.company.com
server4.company.com

We have added aliases named web1 , web2 and web3 for the first three servers. Update server4 to have an alias db1

## Sample Inventory File

web1 ansible_host=server1.company.com
web2 ansible_host=server2.company.com
web3 ansible_host=server3.company.com
db1 ansible_host=server4.company.com

The web servers are linux, but the db server is windows. Add additional parameters in each line to add ansible_connection, ansible_user and password. Use the below table for information about credentials.

Alias	Host	Connection	User	Password
web1	server1.company.com	SSH	root	Password123!
web2	server2.company.com	SSH	root	Password123!
web3	server3.company.com	SSH	root	Password123!
db1	server4.company.com	Windows	administrator	Password123!

Note: For linux use ansible_ssh_pass and for windows use ansible_password. Connector for windows is winrm

web1 ansible_host=server1.company.com ansible_connection=ssh ansible_user=root ansible_ssh_pass=Password123!
web2 ansible_host=server2.company.com ansible_connection=ssh ansible_user=root ansible_ssh_pass=Password123!
web3 ansible_host=server3.company.com ansible_connection=ssh ansible_user=root ansible_ssh_pass=Password123!
db1 ansible_host=server4.company.com ansible_connection=winrm ansible_user=administrator ansible_password=Password123!

We have created a group for web servers. Similarly create a group for database servers named db_servers and add db1 server to it.

## Web Servers
web1 ansible_host=server1.company.com ansible_connection=ssh ansible_user=root ansible_ssh_pass=Password123!
web2 ansible_host=server2.company.com ansible_connection=ssh ansible_user=root ansible_ssh_pass=Password123!
web3 ansible_host=server3.company.com ansible_connection=ssh ansible_user=root ansible_ssh_pass=Password123!

## Database Servers
db1 ansible_host=server4.company.com ansible_connection=winrm ansible_user=administrator ansible_password=Password123!

[web_servers]
web1
web2
web3

[db_servers]
db1

1.

Let us now create a group of groups. Create a new group called all_servers and add the previously created groups web_servers and db_servers to it.

Note: Syntax:

[parent_group:children]

child_group1

child_group2

## Web Servers
web1 ansible_host=server1.company.com ansible_connection=ssh ansible_user=root ansible_ssh_pass=Password123!
web2 ansible_host=server2.company.com ansible_connection=ssh ansible_user=root ansible_ssh_pass=Password123!
web3 ansible_host=server3.company.com ansible_connection=ssh ansible_user=root ansible_ssh_pass=Password123!

## Database Servers
db1 ansible_host=server4.company.com ansible_connection=winrm ansible_user=administrator ansible_password=Password123!

[web_servers]
web1
web2
web3

[db_servers]
db1

[all_servers:children]
web_servers
db_servers

Try and represent the data given in the below table in Ansible Inventory format

Server Alias	Server Name	OS	User	Password
sql_db1	sql01.xyz.com	Linux	root	Lin$Pass
sql_db2	sql02.xyz.com	Linux	root	Lin$Pass
web_node1	web01.xyz.com	Win	administrator	Win$Pass
web_node2	web02.xyz.com	Win	administrator	Win$Pass
web_node3	web03.xyz.com	Win	administrator	Win$Pass

Group the servers together based on this table

Group	Members
db_nodes	sql_db1, sql_db2
web_nodes	web_node1, web_node2, web_node3
boston_nodes	sql_db1, web_node1
dallas_nodes	sql_db2, web_node2, web_node3
us_nodes	boston_nodes, dallas_nodes

sql_db1 ansible_host=sql01.xyz.com ansible_connection=ssh ansible_user=root ansible_ssh_pass=Lin$Pass
sql_db2 ansible_host=sql02.xyz.com ansible_connection=ssh ansible_user=root ansible_ssh_pass=Lin$Pass
web_node1 ansible_host=web01.xyz.com ansible_connection=winrm ansible_user=administrator ansible_password=Win$Pass
web_node2 ansible_host=web02.xyz.com ansible_connection=winrm ansible_user=administrator ansible_password=Win$Pass
web_node3 ansible_host=web03.xyz.com ansible_connection=winrm ansible_user=administrator ansible_password=Win$Pass

[db_nodes]
sql_db1
sql_db2

[web_nodes]
web_node1
web_node2
web_node3

[boston_nodes]
sql_db1
web_node1

[dallas_nodes]
sql_db2
web_node2
web_node3

[us_nodes:children]
boston_nodes
dallas_nodes

3.3 - Inventory Format¶

Introduction¶

Ansible inventory formats offer differ from scenario to scenario.
For small-scale projects, simpler formats are likely required as only a small number of servers are used.
For large-scale projects, there are likely resources spread worldwide carrying out a multitude of functions.
Small projects therefore could get away with simple .ini formats, whilst a yaml-based inventory would be suitable for large-scale projects.

Ini Format¶

The most simple and straightforward format.

[webservers]
web1.example.com
web2.example.com

[dbservers]
db1.example.com
db2.example.com

Servers are grouped under []

YAML Format¶

More structured than the .ini format. An example follows:

all:
  children:
    webservers:
      hosts:
        web1.example.com
        web2.example.com
    dbservers:
      hosts:
        db1.example.com
        db2.example.com

Inventory format should be chosen based on project needs.

3.4 - Grouping and Parent-Child Relationshops¶

Introduction¶

It's important to utilise grouping in inventory files for ease of life and reduction of human error.
Typically, servers are grouped based on aspects such as location and functionality.
In the event of sub-grouping, parent-child relationships can be utilised in Ansible.
For example web servers could act as one group, which could be further split into subgroups based on locations.

Ini Format¶

Subgroups are defined by being listed under [<group name>:children]

[webservers:children]
webservers_us
webservers_eu

[webservers_us]
web1_us.example.com
web2_us.example.com

[webservers_eu]
web1_eu.example.com
web2_eu.example.com

YAML Format¶

all:
  children:
    webservers:
      children:
        webservers_us:
          hosts:
            web1_us.example.com:
              ansible_host: <ip address>
            web2_us.example.com:
              ansible_host: <ip address>
        webservers_eu:
          hosts:
            web1_eu.example.com:
              ansible_host: <ip address>
            web2_eu.example.com:
              ansible_host: <ip address>