Ansible Conditional Statements
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In this lesson, you will learn how to create and run a new Ansible playbook that will demonstrate the use of boolean variables and conditional statements.
By the end of this lesson, you'll understand how to control the execution of tasks based on the value of a boolean variable.
Creating the Playbook with Boolean Variable
Start by creating a new playbook file named conditional_test.yml.
nano conditional_test.ymlIn this playbook, we will target all hosts and define a boolean variable create_file at the top, which will control whether a file should be created or removed.
---
- hosts: all
vars_files:
- secret.yml
vars:
create_file: True
tasks:Let's add a debug message that will show the value of our variable create_file:
- name: Should the file exist?
debug:
msg: "File should exist: {{ create_file }}"Next, add a task to create the file conditional_test_file.txt in the home directory when create_file is true:
- name: Create the file
file:
path: ~/conditional_test_file.txt
state: touch
when: create_file == TrueThis task uses the file module to create a file, and it executes when create_file is true (yes). The state: touch parameter ensures that the file is created if it doesn't exist.
Now, let's add a task to remove the file if create_file is false:
- name: Remove the file
file:
path: ~/conditional_test_file.txt
state: absent
when: not create_file == TrueThis task also uses the file module but with state: absent to remove the file if it exists. It executes when create_file is false (no).
Running the Playbook
With the playbook ready, you can execute it to see the conditional logic in action. To test both conditions, first run the playbook with create_file set to yes, and then change it to no and run it again.
Use this command to run the playbook:
ansible-playbook conditional_test.ymlNow you should see the debug messages stating True for the variable value, the task for creating the file should be changed, and the task for removing the file should be skipped:
Verifying the Results
After running the playbook with create_file set to yes, check that the file was created on the managed nodes:
ansible all -m command -a "ls ~/conditional_test_file.txt" -e @secret.yml
When you set create_file to False and rerun the playbook, use the same command to verify that the file has been removed. Remember that we can supply command line (called extra) variables using the -e argument. You can use this to set create_file to yes or no.
See the JSON example below {create_file: no}:
ansible-playbook conditional_test.yml -e '{create_file: False}'This time, the create file is skipped
Notice that I am supplying the extra variables in JSON format. This is because I am passing a boolean value. If I specify -e "create_file = True", the True will be passed in string format, not as a boolean, since the variable type boolean True is not the same value as the string type "True". This breaks our conditional logic since it expects a boolean value for that variable, not a string value.
If you try this, you'll notice that the file is still deleted if you attempt to set the value like so (this passes a string value):
ansible-playbook conditional_test.yml -e "create_file=True"But, if you pass your extra args in JSON format, it will parse the variable type of True correctly as a boolean:
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