Ad-hoc commands in Ansible are simple, one-time commands that you can run without writing a playbook. They are useful for quick tasks, such as checking the status of a service, copying files, or managing packages. This section will cover the basics of using ad-hoc commands, including practical examples and exercises to help you get hands-on experience.

1. Ad-Hoc Command Structure: The basic structure of an ad-hoc command is:

   ansible <host-pattern> -m <module> -a "<module-arguments>"
   

   • <host-pattern>: Specifies the target hosts.
   • -m <module>: Specifies the module to use.
   • -a "<module-arguments>": Specifies the arguments for the module.

2. Commonly Used Modules:

   • ping: Checks the connectivity of the hosts.
   • command: Executes commands on the remote hosts.
   • shell: Executes shell commands on the remote hosts.
   • copy: Copies files to the remote hosts.
   • yum/apt: Manages packages on the remote hosts.

The ping module is used to check the connectivity of the hosts.

Explanation:

• all: Targets all hosts in the inventory.
• -m ping: Uses the ping module.

The command module is used to run commands on the remote hosts.

Explanation:

• webservers: Targets the webservers group in the inventory.
• -m command: Uses the command module.
• -a "uptime": Runs the uptime command on the remote hosts.

The shell module is used to run shell commands on the remote hosts.

Explanation:

• dbservers: Targets the dbservers group in the inventory.
• -m shell: Uses the shell module.
• -a "df -h": Runs the df -h command on the remote hosts.

The copy module is used to copy files to the remote hosts.

Explanation:

• all: Targets all hosts in the inventory.
• -m copy: Uses the copy module.
• -a "src=/etc/hosts dest=/tmp/hosts": Copies the /etc/hosts file to /tmp/hosts on the remote hosts.

The yum or apt module is used to manage packages on the remote hosts.

Explanation:

• webservers: Targets the webservers group in the inventory.
• -m yum: Uses the yum module (use apt for Debian-based systems).
• -a "name=httpd state=present": Installs the httpd package on the remote hosts.

Use the ping module to check the connectivity of all hosts in your inventory.

Use the shell module to check the disk usage on all hosts in the dbservers group.

Use the copy module to copy a file from your local machine to the /tmp directory on all hosts.

Use the yum or apt module to install the nginx package on all hosts in the webservers group.

• Incorrect Module Name: Ensure you use the correct module name. For example, use yum for Red Hat-based systems and apt for Debian-based systems.
• Quoting Arguments: Always quote the arguments passed to the -a option to avoid issues with spaces and special characters.
• Inventory File: Ensure your inventory file is correctly configured and accessible.

Ad-hoc commands are a powerful feature in Ansible that allow you to perform quick tasks without writing a playbook. By mastering ad-hoc commands, you can efficiently manage and troubleshoot your infrastructure. In the next section, we will dive deeper into Ansible modules and how to use them effectively.