The Problem

Your playbook uses pre_tasks for setup before roles, but issues occur:

bash
fatal: [server]: FAILED! => {"msg": "pre_tasks failed before roles could execute"}

Or handlers notified in pre_tasks don't run until after roles:

yaml
pre_tasks:
  - name: Configure
    template: ...
    notify: restart service
# Handler doesn't run until after all roles complete

Or pre_tasks don't run at all when expected.

Why This Happens

pre_tasks errors stem from:

Handler timing - Handlers from pre_tasks wait until roles complete.

Variable scope - Variables not available when pre_tasks need them.

pre_tasks failure stops roles - If pre_tasks fail, roles never execute.

Serial interaction - pre_tasks run for each serial batch.

Condition confusion - Conditions on pre_tasks vs play.

Understanding pre_tasks

pre_tasks run before roles in a play:

```yaml - hosts: webservers pre_tasks: - name: Setup before roles debug: msg: "Pre-task running"

roles: - webserver

tasks: - name: After roles debug: msg: "Regular task" ```

Execution order: pre_tasks -> roles -> tasks -> handlers

Diagnosing the Issue

Run with verbose output:

bash
ansible-playbook playbook.yml -vv

Check execution order:

bash
ansible-playbook playbook.yml --list-tasks
# Shows pre_tasks first, then role tasks

Debug handler notifications:

```yaml pre_tasks: - name: Notify handler command: /opt/setup.sh notify: my_handler register: notify_check

  • debug:
  • msg: "Handler notified: {{ notify_check }}"
  • `

The Fix

Fix 1: Flush Handlers in pre_tasks

Handlers from pre_tasks wait for roles - flush explicitly:

```yaml - hosts: webservers pre_tasks: - name: Update config template: src: app.conf.j2 dest: /etc/app.conf notify: restart app

  • name: Flush handlers before roles
  • meta: flush_handlers
  • # Handler runs now, before roles

roles: - deploy_app # App already restarted, roles proceed with running service ```

Fix 2: Handle pre_tasks Failure Gracefully

pre_tasks failure stops entire play - use block/rescue:

```yaml - hosts: webservers pre_tasks: - name: Setup with error handling block: - name: Critical setup command: /opt/critical-setup.sh

  • name: Optional setup
  • command: /opt/optional-setup.sh
  • ignore_errors: yes

rescue: - name: Handle setup failure debug: msg: "Setup failed, continuing with degraded state"

roles: - app # Roles run even if optional setup failed ```

Fix 3: Define Variables for pre_tasks

Variables must exist before pre_tasks:

```yaml # WRONG - variable undefined for pre_tasks - hosts: webservers pre_tasks: - name: Use undefined variable debug: msg: "{{ app_name }}"

vars: app_name: myapp # Defined after pre_tasks block

# CORRECT - vars before pre_tasks - hosts: webservers vars: app_name: myapp

pre_tasks: - name: Use defined variable debug: msg: "{{ app_name }}" ```

Fix 4: pre_tasks with Serial

pre_tasks run for EACH serial batch:

yaml
- hosts: webservers
  serial: 3
  pre_tasks:
    - name: Setup
      debug:
        msg: "Pre-task for {{ inventory_hostname }}"
      # Runs 4 times if 10 hosts (4 batches)

For one-time pre_task with serial:

yaml
- hosts: webservers
  serial: 3
  pre_tasks:
    - name: One-time setup
      command: /opt/global-setup.sh
      run_once: yes
      # Runs once, not per batch

Fix 5: pre_tasks Conditions

Conditions apply to individual pre_tasks:

```yaml - hosts: webservers pre_tasks: - name: Conditional pre-task debug: msg: "Only for Debian" when: ansible_os_family == "Debian"

  • name: Always runs
  • debug:
  • msg: "No condition"
  • `

Play-level conditions don't affect pre_tasks:

yaml
- hosts: webservers
  when: some_condition  # This doesn't affect pre_tasks
  pre_tasks:
    - name: Still runs
      debug:
        msg: "pre_tasks ignore play-level when"

Fix 6: Gather Facts in pre_tasks

Disable default fact gathering, gather in pre_tasks:

```yaml - hosts: webservers gather_facts: no pre_tasks: - name: Gather facts selectively setup: filter: ansible_os_family # Faster than full fact gathering

  • name: Use minimal facts
  • debug:
  • msg: "{{ ansible_os_family }}"
  • `

Fix 7: pre_tasks Common Patterns

Load balancer removal before deployment:

```yaml - hosts: webservers pre_tasks: - name: Disable in load balancer command: lb-cli disable {{ inventory_hostname }} delegate_to: lb-server

  • name: Wait for connections drain
  • wait_for:
  • port: 80
  • state: drained
  • timeout: 30

roles: - deploy

post_tasks: - name: Enable in load balancer command: lb-cli enable {{ inventory_hostname }} delegate_to: lb-server ```

Database migration before app update:

```yaml - hosts: appservers pre_tasks: - name: Run migrations command: /opt/app/migrate.sh delegate_to: db-server run_once: yes

roles: - app-update ```

Fix 8: Verify Facts for pre_tasks

Check facts exist before using:

```yaml - hosts: webservers pre_tasks: - name: Verify required facts assert: that: - ansible_os_family is defined - ansible_default_ipv4.address is defined fail_msg: "Required facts not available" success_msg: "Facts verified"

roles: - configure ```

Verifying the Fix

Test pre_tasks execution order:

```yaml # test_pre.yml - hosts: localhost gather_facts: no pre_tasks: - name: Pre-task 1 debug: msg: "First pre-task"

  • name: Pre-task 2
  • debug:
  • msg: "Second pre-task"

roles: - role: test_role # Create a simple test role

tasks: - name: Regular task debug: msg: "After roles" ```

Run:

bash
ansible-playbook test_pre.yml -v

Expected order: `` TASK [Pre-task 1] *********************************************************** TASK [Pre-task 2] *********************************************************** TASK [test_role : main] *********************************************************** TASK [Regular task] ***********************************************************

Prevention

Document pre_tasks purpose:

yaml
- hosts: webservers
  # pre_tasks: Remove from load balancer before deployment
  pre_tasks:
    - name: Disable in LB
      ...

Add pre-flight checks:

yaml
pre_tasks:
  - name: Verify prerequisites
    assert:
      that:
        - required_var is defined
      fail_msg: "Prerequisites not met"