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Three optional Ansible playbooks can live in a scenario directory. The runner discovers and invokes them automatically at the right point in the execution cycle.

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Execution Flow

2501-runner run -s <scenario>
        │
        ▼
┌───────────────┐
│  Pre-flight   │  verify DB, gateway/engine, ansible availability
└───────┬───────┘
        │
        ▼
┌───────────────┐
│   Provision   │  resolve host + agent from DB, flush agent memory
└───────┬───────┘
        │
        ├─── restore.yml ──► silent pre-clean (errors suppressed)
        │
        ▼
┌───────────────┐
│    Prepare    │  run prepare.yml  →  introduce the failure condition
└───────┬───────┘    (abort if fails)
        │
        ▼
┌───────────────┐
│    Execute    │  dispatch task via gateway / task / ticket
│               │  agent investigates and acts on the target host
└───────┬───────┘
        │
        ▼
┌───────────────┐
│   Validate    │  evaluate pattern_match / task_count / status rules
│               │  run validate.yml  →  check actual machine state
└───────┬───────┘
        │
        ▼
┌───────────────┐
│    Restore    │  run restore.yml  →  reset host to clean baseline
└───────┬───────┘    (non-fatal if fails)
        │
        ▼
┌───────────────┐
│    Report     │  print summary, persist ScenarioReport to DB
└───────────────┘

​
prepare.yml

Runs before the agent executes. Use it to introduce the failure condition the scenario is benchmarking. Before prepare.yml runs, the runner silently executes restore.yml with errors suppressed. This clears leftover state from any previous failed run so each execution starts from a known baseline: even when the prior run was interrupted mid-way. If prepare.yml itself fails, execution is aborted and the scenario is marked as failed. 
---
- name: Deploy broken nginx configuration
  hosts: all
  become: true
  tasks:
    - name: Ensure nginx is installed
      apt:
        name: nginx
        state: present
        update_cache: true

    - name: Write a config with a syntax error (missing semicolon after listen 80)
      copy:
        dest: /etc/nginx/sites-available/default
        content: |
          server {
            listen 80
            root /var/www/html;
            index index.html;
          }

    - name: Attempt reload: this will fail, which is intentional
      systemd:
        name: nginx
        state: restarted
      ignore_errors: true

​
restore.yml

Runs after validation, during cleanup. Use it to reset the host to a clean baseline. Restore failures are non-fatal: the runner logs a warning and continues. Write your restore playbooks defensively with ignore_errors: true on steps that may fail on an already-clean host. 
---
- name: Reset nginx to clean state
  hosts: all
  become: true
  tasks:
    - name: Stop nginx
      systemd:
        name: nginx
        state: stopped
        enabled: false
      ignore_errors: true

    - name: Remove injected config
      file:
        path: /etc/nginx/sites-available/default
        state: absent
      ignore_errors: true

​
validate.yml

Runs after execution as part of the validation phase. Use it to verify that the agent’s actions actually worked: service status, file contents, port availability, process list. Declared in scenario.json as an ansible validator: 
{
  "label": "Nginx is healthy",
  "validator": "ansible",
  "ansiblePath": "validate.yml"
}
A non-zero exit code fails the resolution gate and marks the scenario as failed. 
---
- name: Verify nginx is healthy
  hosts: all
  become: true
  tasks:
    - name: Config syntax is valid
      command: nginx -t

    - name: Service is active
      command: systemctl is-active nginx

    - name: Port 80 is responding
      uri:
        url: http://localhost:80
        status_code: [200, 301, 302]

​
Using Environment Variables

Variables from /etc/2501/env.runner are available in all playbooks via lookup('env', ...): 
- name: Clone a private repository
  git:
    repo: "https://{{ lookup('env', 'GH_TOKEN') }}@github.com/your-org/fixtures.git"
    dest: /opt/fixtures

​
inventory.ini

The runner needs an Ansible inventory to know which hosts to target and how to reach them. Place an inventory.ini file in the scenario directory: the runner detects it automatically and passes it to every ansible-playbook call for that scenario. Standard Ansible INI format: 
[web]
sandbox-web-01 ansible_host=10.0.1.10 ansible_user=ubuntu ansible_port=22

[db]
sandbox-db-01 ansible_host=10.0.1.20 ansible_user=ubuntu ansible_port=22

[all:vars]
ansible_ssh_private_key_file=/etc/2501/keys/sandbox.pem
The hostnames must match the logical names used in scenario.json so the runner can correlate them correctly.
If no inventory.ini is present, ansible-playbook runs without an explicit inventory. Your playbooks won’t be able to reach any hosts. Always include inventory.ini when your scenario has playbooks.