linuxexpert-practice-labs/labs/ex294/7-3-conditionals/README.md

EX294 7.3: Conditionals

Make tasks run only where they apply: on hosts that have a disk, on hosts in a group with enough memory, and when an extra variable asks for it.

Before you start

This VM is the control node. The lab creates the user greg (password Lab-Pass-1) and installs ansible-core. Work as greg, in /home/greg/ansible: its ansible.cfg reads the inventory inventory, logs in to the nodes as devops with greg's SSH key, and becomes root.

The managed nodes node1 (10.99.1.11), node2 (10.99.1.12) and node3 (10.99.1.13) are AlmaLinux 10 containers. node1 is in the group webservers, node2 and node3 in dbservers. Containers share the VM's memory and disks, so the lab gives each node its own memory size and disks, as Ansible's facts see them: look with ansible all -m setup -a 'filter=ansible_memtotal_mb' and filter=ansible_devices. For a root shell on a node, sudo podman exec -it node1 bash.

Tasks

1. Write /home/greg/ansible/disk.yml, which prints a message of your choice on hosts that have a disk vdc, and the message Disk vdc does not exist on the others. Each host prints exactly one of the two.
2. Write /home/greg/ansible/mariadb.yml, with one play that targets all, to install mariadb-server only on hosts in the dbservers group with at least 2 GiB of memory. Run it; the task is skipped on the web servers.
3. Write /home/greg/ansible/upgrade.yml with a task that prints Upgrading and runs only when -e upgrade=true is given. It's skipped with -e upgrade=false and without -e.

Hints

• 'vdc' in ansible_facts['devices']; a when needs no braces.
• 'dbservers' in group_names, ansible_facts['memtotal_mb'] >= 2048; a list under when means all of them.
• Extra vars are strings: upgrade | default(false) | bool.
• Run with -v to see false_condition on skipped hosts.