Inventory

The inventory is an important place; setting up the inventory, group vars and host vars correctly helps to keep your data dry, ensures that it’s easy to find data and that you are able to continue with the correct structure for years to come.

Inventory file

The inventory file describes the targets available.

Text or executable?

Remember that a non-executable file (a text file) is simply read, where as an executable file will be executed and the output is used as an inventory. The executable version would be called a “dynamic inventory”.

A non-executable file is a text file, that contains the hosts and groups the hosts. We’ll be using this type of inventory in the next chapters.

A few examples of dynamic inventory scripts:

• AWS
• Azure
• GCP

Formats

The inventory file can be written in INI, YAML and even JSON.

I would advice to use the INI-format as it’s pretty easy to read and write.

Locations

By default the inventory is placed in /etc/ansible/hosts. This would be a system-wide inventory, which is not very common to use.

You can override the inventory by specifying the -i parameter:

ansible-playbook -i /path/to/inventory my_playbook.yml

I would recommend to place an ansible.cfg, referring to an inventory in the project or repository you are working on.

Here is an example of an inventory in the INI-format:

ansible.cfg

[defaults]
inventory = inventory

inventory/hosts

[webservers]
node-a
node-b

[databaseservers]
node-c
node-d

[development]
node-a
node-c

[production]
node-a
node-d

[applicationx:children]
webservers
databaseservers

Good to know:

• Hosts can be in multiple groups.
• You can place variables and values in an inventory, host_vars or group_vars would be a better place.
• You can make cross-selections. This is described in the targeting chapter.
• Groups-in-groups are possible, using :children.
• If ansible.cfg refers to an inventory, this inventory can be a file or directory.
• You can use -i to override the inventory. A drawback is that these “runtime” options are not stored as code.

Assignment

Create a new directory somewhere on your system, and create a new file in that directory called ansible.cfg file that refers to an inventory file.

Write an inventory (the solution I used will use ini format, you can pick a different format) with the following groups:

• webservers
• databaseservers
• netherlands
• switzerland

Add the following hosts:

• node-1 (a Dutch webserver)
• node-2 (a Swiss webserver)
• node-3 (a Dutch database server)
• node-4 (a Swiss database server)

Make a group of groups: europe that contains netherlands and switzerland.

Verify

Run ansible all --list-hosts. You should see this output:

  hosts (4):
    node-1
    node-2
    node-3
    node-4

Run ansible-inventory --list. You should see this output:

{
    "_meta": {
        "hostvars": {}
    },
    "all": {
        "children": [
            "ungrouped",
            "webservers",
            "databaseservers",
            "europe"
        ]
    },
    "databaseservers": {
        "hosts": [
            "node-3",
            "node-4"
        ]
    },
    "europe": {
        "children": [
            "netherlands",
            "switzerland"
        ]
    },
    "netherlands": {
        "hosts": [
            "node-1",
            "node-3"
        ]
    },
    "switzerland": {
        "hosts": [
            "node-2",
            "node-4"
        ]
    },
    "webservers": {
        "hosts": [
            "node-1",
            "node-2"
        ]
    }
}

Run ansible-inventory --graph. You should see this output:

@all:
  |--@ungrouped:
  |--@webservers:
  |  |--node-1
  |  |--node-2
  |--@databaseservers:
  |  |--node-3
  |  |--node-4
  |--@europe:
  |  |--@netherlands:
  |  |  |--node-1
  |  |  |--node-3
  |  |--@switzerland:
  |  |  |--node-2
  |  |  |--node-4@all:
  |--@ungrouped:
  |--@webservers:
  |  |--node-1
  |  |--node-2
  |--@databaseservers:
  |  |--node-3
  |  |--node-4
  |--@europe:
  |  |--@netherlands:
  |  |  |--node-1
  |  |  |--node-3
  |  |--@switzerland:
  |  |  |--node-2
  |  |  |--node-4

Solution

The solution can be found in the solution directory.

NOTE: This assignment is required for further chapters.