linuxexpert-practice-labs/labs/ex294/7-4-error-handling/README.md

EX294 7.4: Error handling

Recover from a failure with block and rescue, decide what counts as a failure, and stop a whole play when one host fails.

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) and node2 (10.99.1.12) are AlmaLinux 10 containers, in the group nodes. For a root shell on a node, sudo podman exec -it node1 bash.

Tasks

1. Write /home/greg/ansible/block.yml for all nodes: a block that tries to start a service that doesn't exist, a rescue that prints the failed task's name and message, and an always that appends a line to /var/log/block.log. The recap shows rescued=1 and failed=0 on every node, and the log file has the line.
2. Write /home/greg/ansible/grep.yml, which runs grep on the nodes for a pattern that isn't in the file, such as lab-pattern, in the file named by the variable grep_file (by default /etc/hosts). Make the task fail only if the file is missing: the playbook passes as it is, and fails with -e grep_file=/etc/no-such-file.
3. Write /home/greg/ansible/stop.yml: a play on all nodes with a task that fails on node1 only, then at least one more task. Make the play stop on every host as soon as node1 fails: the output shows NO MORE HOSTS LEFT, and the later tasks run on no host.

Hints

• In rescue, ansible_failed_task.name and ansible_failed_result.msg.
• lineinfile with create: true makes the log file if it's missing.
• grep exits 0 on a match, 1 on none and 2 on an error such as a missing file; register the result and use failed_when on its rc. ignore_errors doesn't change what a failure is.
• /bin/false with when: inventory_hostname == 'node1', and a play keyword from the chapter's table.