How to Use Static and Dynamic Inventories in Ansible?

Ansible is a powerful automation tool that allows you to manage and configure systems, deploy software, and orchestrate advanced IT tasks such as continuous deployments or zero downtime rolling updates. One of the key components of Ansible is the inventory file, which describes the hosts and groups of hosts upon which commands, modules, and tasks in a playbook operate.

In this article, we'll explore how to use both static and dynamic inventories in Ansible, complete with examples and their outputs.

Static Inventories

Static inventories are the simplest way to manage and organize your servers. They are defined in INI or YAML format and remain unchanged unless manually modified. Here's an example of a static inventory in INI format:

[webservers]
webserver1.example.com
webserver2.example.com

[dbservers]
dbserver1.example.com

In this example, we have two groups ? webservers and dbservers. Each group contains the hostnames of the servers in that group.

You can use these groups in your playbooks to target specific servers for different tasks:

- hosts: webservers
  tasks:
    - name: ensure apache is at the latest version
      ansible.builtin.yum:
        name: httpd
        state: latest

Using Variables in Static Inventory

You can define variables directly in your static inventory file. These variables can be used in your playbooks:

[webservers]
webserver1.example.com http_port=80 max_clients=200

[dbservers]
dbserver1.example.com mysql_port=3306

In your playbook template, you can reference these variables:

Listen {{ http_port }}
MaxClients {{ max_clients }}

Using Child Groups and Aliases

Static inventories support hierarchical organization through child groups and host aliases:

[atlanta]
host1
host2

[raleigh]
host3
host4

[southeast:children]
atlanta
raleigh

[webservers]
web1 ansible_host=webserver1.example.com
web2 ansible_host=webserver2.example.com

The southeast group includes all hosts from both atlanta and raleigh groups, while aliases like web1 provide readable names for actual hostnames.

Dynamic Inventories

While static inventories are easy to understand, they become difficult to manage as infrastructure scales. Dynamic inventories are scripts that automatically generate inventory data from external sources like cloud providers, databases, or APIs.

AWS Dynamic Inventory

To use AWS dynamic inventory, install the required dependencies and configure access:

pip install boto3
export AWS_ACCESS_KEY_ID=your_access_key
export AWS_SECRET_ACCESS_KEY=your_secret_key

Create an AWS inventory configuration file aws_ec2.yml:

plugin: aws_ec2
regions:
  - us-west-2
  - us-east-1
filters:
  instance-state-name: running
keyed_groups:
  - key: tags.Environment
    prefix: env
  - key: instance_type
    prefix: type

Use the dynamic inventory in your playbooks:

ansible-playbook -i aws_ec2.yml playbook.yml

Docker Dynamic Inventory

For Docker containers, create a docker.yml inventory file:

plugin: docker_swarm
docker_host: unix://var/run/docker.sock
compose:
  ansible_host: ansible_docker_swarm_node_attributes.Addr
keyed_groups:
  - key: ansible_docker_swarm_node_attributes.Role
    prefix: role

Run playbooks against Docker containers:

ansible-playbook -i docker.yml playbook.yml

Comparison

Conclusion

Static inventories work well for small, stable environments with predictable infrastructure, while dynamic inventories excel in cloud and containerized environments where infrastructure changes frequently. Choose based on your environment's scale, change frequency, and complexity requirements.