Running Ansible in CHECK/DIFF mode

Ansible Check and Diff modes

Check mode

check mode is a way for Ansible to do a "Dry Run" and validate your playbook without making any actual changes to remote systems. Simply adding --check to the end of your ansible-playbook command will run ansible in check mode. This is a great way to test your playbook during the development cycle.

Here is an example of running an ansible play in checkmode

ansible-playbook -i hosts -K playbook-apt-install.yml --check

After running in check mode, you should see output similar to below.

PLAY RECAP ******************************************************************************************************************
node3                      : ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

Diff mode

diff mode gives a verbose before-and-after comparison of changes being made.

Here's how to run it.

ansible-playbook -i hosts -K playbook-apt-install.yml --check

You will get output like below in regards to what changes on the system will be made.

TASK [ensure NMAP is installed.] ********************************************************************************************
Suggested packages:
  ncat ndiff zenmap
The following NEW packages will be installed:
0 upgraded, 1 newly installed, 0 to remove and 85 not upgraded.

Combining Check and Diff

Although not required, it's common practice to combine both check and diff together. This way you can do a Dry Run of your playbook AND get all the changes that would be made.

ansible-playbook -i hosts -K playbook-apt-install.yml --check --diff