Running Ad-hoc Commands
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In this lesson, we'll focus on executing ad-hoc commands in Ansible. Ad-hoc commands are a quick and easy way to perform tasks without writing a full playbook. Specifically, we'll learn how to use an ad-hoc command to delete the file we created in our previous lesson. By the end of this lesson, you'll understand how to use Ansible for simple, direct task execution across your managed nodes.
What are Ad-hoc Commands?
Ad-hoc commands in Ansible allow you to execute simple tasks at the command line without needing to write a playbook. They are great for tasks you need to perform quickly, but they are not idempotent like a playbook, so they should be used judiciously.
Using ansible-doc for Module Information
Before we run our ad-hoc command, let's first understand how to use the ansible-doc command to get information about the file module. The file module is versatile and can be used for various file operations, including creating, deleting, or modifying files and directories.
To view the documentation for the file module, run:
ansible-doc filePro tip: You can search the file by pressing '/' and then typing in a search query. Pressing 'n' will show the next occurrence of your search pattern.
This command will display detailed information about the file module, including how to specify the path to a file and set its state. Look for the state option and notice how setting it to absent will remove a file.
Deleting the File with an Ad-hoc Command
Now, let's use an ad-hoc command to delete the file /tmp/ansible_created_this_file.txt that we created earlier. The command is as follows:
ansible all -m file -a "path=/tmp/ansible_created_this_file.txt state=absent"Here's what this command does:
When I execute the command, I see the following output:
Here is a breakdown of the output we see:
Verifying File Removal
After executing the ad-hoc command, it's good practice to verify that the command did what we expected and the file has indeed been removed on all hosts.
First, check on the controller node:
ls /tmpThis will list the contents of the /tmp directory on the controller. Ensure that ansible_created_this_file.txt is no longer listed.
Next, verify on the managed nodes. Assuming you have two managed nodes named managed-node-1 and managed-node-2, run:
ssh managed-node-1 -t "ls /tmp"
ssh managed-node-2 -t "ls /tmp"These commands will SSH into each managed node and list the contents of the /tmp directory, allowing you to confirm that the file has been removed on both nodes.
As you can see, the files have been deleted all hosts in our Ansible inventory!
Important: Ad-hoc commands are NOT idempotent
Remember, while ad-hoc commands are powerful, they lack the idempotency and organization of playbooks, making them more suited for one-off or immediate tasks.
Idempotence is the property of certain operations in mathematics and computer science whereby they can be applied multiple times without changing the result beyond the initial application.
Conclusion
Ad-hoc commands in Ansible provide a quick and efficient way to perform tasks without the need for a full playbook. They are particularly useful for straightforward tasks like file manipulation.
Understanding how to use ansible-doc is also an important skill. It allows you to explore the capabilities and options of various Ansible modules directly from the command line, aiding in both ad-hoc commands and playbook development.
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