Managed nodes are the remote systems that Ansible automates and orchestrates. Each managed node must meet certain requirements and displays important characteristics that ensure seamless automation and control:

• No Agent Required: Managed nodes operate agentlessly—there is no need to install any special software or agent on the node. Ansible connects remotely via standard protocols like SSH (for Linux/UNIX) or WinRM (for Windows).
• Remote Connectivity: The control node communicates with managed nodes over the network, most often using SSH. Reliable and secure remote access is fundamental for orchestration.
• OS Flexibility: Ansible supports a wide range of operating systems, allowing managed nodes to run various distributions, including Linux, BSD, UNIX, MacOS, and Windows.
• Python (or PowerShell for Windows): Most managed nodes require Python (usually already available by default on UNIX-like systems). Windows managed nodes require PowerShell and WinRM for communication.
• Minimal Configuration: Managed nodes do not require extensive setup beyond enabling remote connectivity and ensuring the control node has adequate permissions (such as SSH key-based authentication or Windows credentials).
• Independence from Control Node: Managed nodes remain autonomous and only receive instructions from the control node when necessary; they are not dependent on the control node for continued operation.
• Inventory Inclusion: Each managed node must be listed or referred to in the Ansible inventory file in order to be targeted by playbooks and tasks.

Ansible uses inventory files to define the set of managed nodes it can interact with. One of the most common formats is INI-style inventory, which groups hosts and allows for the definition of variables. Below is a basic structure and use-case example:

[webservers]
web01 ansible_host=192.168.10.11
web02 ansible_host=192.168.10.12

[dbservers]
db01 ansible_host=192.168.10.21 ansible_user=postgres
db02 ansible_host=192.168.10.22 ansible_user=postgres

[loadbalancers]
lb01 ansible_host=192.168.10.31 ansible_connection=ssh

[all:vars]
ansible_user=admin
ansible_ssh_private_key_file=~/.ssh/id_rsa
ansible_python_interpreter=/usr/bin/python3

• [webservers], [dbservers], [loadbalancers]: These define logical groups of hosts. You can target these groups in playbooks.
• ansible_host: This variable overrides the hostname with an IP or DNS address for remote connectivity.
• ansible_user: Defines the login user Ansible should use for the specified host or group.
• ansible_connection: Specifies the connection type (e.g., SSH, WinRM).
• [all:vars]: Sets global variables applied to all hosts, helping reduce redundancy in the inventory.

This example showcases a clear, organized way to define multiple nodes and their characteristics using the INI format.

Before Ansible can successfully manage a node, certain prerequisites and best practices should be met. Here is a step-by-step checklist to prepare your managed nodes:

1. Ensure Network Connectivity:
   • Verify that the managed node is reachable from the control node, typically over SSH (Linux/UNIX) or WinRM (Windows).
2. Install Required Language Runtime:
   • For Linux/UNIX: Make sure Python (2.7 or 3.5+) is installed. Most distributions include Python by default.
   • For Windows: Ensure PowerShell and WinRM are properly configured.
3. Create an Ansible User:
   • Add a dedicated system user (commonly "ansible") on the managed node for automation tasks.
   • Set a strong password or configure key-based authentication for this user.
   • Grant sudo privileges if tasks require elevated permissions (follow recommended security policies).
4. Configure Authentication:
   • Set up SSH public key authentication from the control node to the managed node for the Ansible user (Linux/UNIX).
   • For Windows, configure WinRM and provide valid credentials with administrative rights.
5. Install and Verify Dependencies:
   • For Linux/UNIX nodes, confirm that Python dependencies required by your playbooks or roles are installed.
   • For network devices or special platforms, install any necessary modules or collections compatible with Ansible.
6. Update the System:
   • Ensure the managed node is up to date with the latest security patches and package updates.
7. Inventory Entry:
   • Verify the managed node is listed in your Ansible inventory file, with the correct IP address, hostname, and required variables defined.
8. Test Connection:
   • From the control node, use Ansible to run a simple ping module test: ansible all -m ping.
   • Resolve any issues that prevent communication or privilege escalation (sudo).

Completing this checklist ensures each managed node is properly prepared for reliable automation with Ansible.

Targeting managed nodes with Ansible playbooks is both flexible and precise. This example demonstrates how to define plays that run against different groups or specific hosts defined in your inventory.

1. Target a Group of Hosts:
   • Define which hosts the play should run against using the hosts: keyword. This can reference an inventory group, such as webservers.

   ---
   - name: Restart webservers
     hosts: webservers
     tasks:
       - name: Restart Apache service
         ansible.builtin.service:
           name: httpd
           state: restarted
   

2. Target a Single Host:
   • Use the hostname from your inventory to target a single node directly.

   ---
   - name: Configure single node
     hosts: web01
     tasks:
       - name: Check disk usage
         ansible.builtin.command: df -h
   

3. Target Multiple Groups or Hosts:
   • Specify more than one group or individual host, separated by commas.

   ---
   - name: Update all web and database servers
     hosts: webservers,dbservers
     tasks:
       - name: Ensure NTP is installed
         ansible.builtin.yum:
           name: ntp
           state: present
   

4. Exclude Hosts Using Patterns:
   • You can use patterns to include or exclude nodes. For example, target all hosts except one.

   ---
   - name: Apply changes everywhere except one node
     hosts: all:!web02
     tasks:
       - name: Display hostname
         ansible.builtin.command: hostname
   

This approach allows for powerful targeting strategies, enabling automation across specific managed nodes or groups as needed. Adjust the hosts: directive in your playbook to match your organizational needs and inventory structure.

Successfully managing nodes with Ansible requires more than just proper configuration — it involves following best practices that promote maintainability, reliability, and scalability. Below are key recommendations to optimize your managed node strategy:

1. Use Descriptive Inventory Groups:
   • Organize your inventory logically by function (e.g., [webservers], [dbservers]) or environment (e.g., [production], [staging]).
2. Limit Privilege Escalation:
   • Use become only when necessary, and restrict administrative access tightly. Avoid running tasks as root unless required.
3. Use SSH Key Authentication:
   • Leverage secure SSH key pairs for Linux/UNIX systems instead of passwords to reduce the risk of credential leaks.
4. Keep Nodes Updated:
   • Ensure your managed nodes have current operating system updates, including Python and libraries required for your playbooks.
5. Avoid Hardcoding Credentials:
   • Use Ansible Vault or environment variables to securely manage sensitive data such as API keys, passwords, and tokens.
6. Validate Node Readiness:
   • Run connection checks like ansible all -m ping regularly to confirm nodes are reachable and responsive before deploying configurations.
7. Use Host-Specific Variables Sparingly:
   • Favor group variables over host variables unless specific customization is needed. This keeps your inventory files easier to manage at scale.
8. Enforce Consistent Python Versions:
   • Ensure nodes run the same or compatible versions of Python to prevent playbook inconsistencies.

Applying these practices across all managed nodes helps ensure your Ansible automation environment is secure, stable, and future-ready.

Understanding managed nodes in Ansible requires familiarity with a few key Ansible concepts. Here are short descriptions of the foundational terms and how they relate to managed nodes:

• Control Node: The system where Ansible is installed and from which automation is initiated. The control node sends instructions to managed nodes but is not itself managed by Ansible.
• Managed Node (Host): Any device—such as a server, network appliance, or virtual machine—that is configured, maintained, or automated by Ansible. The managed node receives instructions from the control node, and no special software is required on these nodes.
• Inventory: A file or source (in INI, YAML, or dynamic script format) that lists all managed nodes Ansible can target. Inventory files let you group nodes, assign variables, and define connection details.
• Modules: Discrete units of code that Ansible executes on managed nodes to perform tasks such as installing packages, configuring services, or copying files.
• Tasks: The smallest unit of action in Ansible, describing a single operation (often using a module) executed on a managed node.
• Playbook: A YAML-formatted file that defines and orchestrates a set of plays and tasks across one or more managed nodes. Playbooks ensure consistent automation and repeatability.
• Roles: A way to organize playbooks and tasks into reusable groups, making it easier to maintain complex automation projects across many managed nodes.
• Collections: Bundles of related content (roles, modules, plugins, documentation, and more) for more robust and portable automation.
• Facts: Data collected from managed nodes during execution, such as OS type, IP addresses, or available memory. Facts help make playbooks dynamic and adaptable.
• Variables: Define values that tailor the behavior of playbooks, roles, or tasks for specific managed nodes or environments.
• Templates: Files with placeholders that Ansible fills in using variables or facts to create dynamic, context-aware configuration files for managed nodes.
• Plugins: Extensions that enhance Ansible’s core capabilities, such as new connection types, output formatting, or data manipulation, helping manage nodes in more sophisticated scenarios.

Referencing these concepts ensures clarity when discussing managed nodes and enables more effective Ansible automation design and execution.