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Ansible Inventory

Table of Contents

Introduction

This document described the implementation of the Ansible Inventory on this project.

It used a mix of a passwordstode database and static files to maintain all host information and properties.

Introduction to Ansible Inventory

Ansible can work against multiple systems or machines in an infrastructure, called hosts at the same time, using a list or group of lists know as an inventory.

Once the inventory is defined, you can select the hosts or groups where you want that Ansible runs against. The inventory is comprised of several files and scripts located under the k8s-infra/ansible/inventory folder.

The two most important files are: * hosts.yml: YAML file with group structure information as well as group variable assignment * pass_inventory.py: Python script that dynamically builds the inventory from the passwordstore project. This task is done automatically when Ansible is executed.

Remark: More information on the Ansible Inventory and how to build it is defined within the [Ansible User Guide](https://docs.ansible.com/ansible/latest/user_guide/intro_inventory.html).

hosts.yml file

This file contains static information for the inventory such as: * Group * Group hierarchy * Group variables * Host-Group assignment - although we won’t use it in this project

Here is a sample of a hosts yaml file designed using YAML.

all: # keys must be unique, i.e. only one 'hosts' per group
    hosts:
        host1:
        host2:
            host_var: value
    vars: # variables for group all (i.e. variables that will be inherited from all hosts)
        group_all_var: value
    children: # child groups. key order does not matter, indentation does
        other_group: # other_group is a child of the all group
            children: # group hierarchy can go on...
                group_x:
                    hosts:
                        host5:
                group_y:
                    hosts:
                        host6:
            vars:
                g2_var2: value3
            hosts:
                host4:
                    ansible_host: 127.0.0.1
        last_group:
            hosts:
                host1:
            vars:
                group_last_var: value

More information on these documents are available:

This project already includes a static inventory, at the ../inventory/hosts.yml file.

Groups

Ansible hosts can be grouped into…​well groups. This allows the execution of playbooks and the definition of variables in a common matter for different hosts.

Group definition is done inside the ansible/inventory/hosts.yml file using yaml format. In this file are the definitions of groups as well as the variable values assigned to each group.

Host group assignment is made in passstore by managing entries in the provider/host/groups folder being each entry a group to which the host belongs.

├── provider
|   ├── host_1
│   │   ├── groups
│   │   │   ├── group_1
│   │   │   ├── group_2
│   │   │   ├── group_3
|   ├── host_2
│   │   ├── groups
│   │   │   ├── group_2
│   │   │   ├── group_3

For instance, we wanted to define the ports that a k8s master needs to open. This has been done in the hosts.yml file having the following variable assigned to the masters group, which is also inside a group structure so other variables are inherited.

firewalld_public_ports:
  - 6443/tcp
  - 10250/tcp
  - 10255/tcp
  - 8472/udp
  - 30000-32767/tcp

For information regarding actually managing host-group assignment check the [passstore_manage_host_groups section](#passstore_manage_host_groups).

pass_inventory.py Inventory Python script

This Python script build the Ansible Inventory from the passwordstore database.

To collect information on a host execute the following command.

./ansible/inventory/pass_inventory.py --host (1)

  1. Name of the host in the Ansible inventory.

Example

./ansible/inventory/pass_inventory.py --host ocp-xyz-tmp-bootstrap-server

To list all the inventory simply execute with the --list attribute.

./ansible/inventory/pass_inventory.py --list