Orchestration — Coordinating Many Tasks

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Learning Objectives

Tell automation and orchestration apart
Read a basic Ansible playbook
Build a step runner that rolls back on failure

Automation vs Orchestration

Automation does one task automatically (push a config). Orchestration coordinates many automated tasks together, in order, often across systems: provision a VLAN -> update the firewall rule -> update DNS -> notify Slack. Ansible playbooks are a common orchestration tool.

Real Ansible YAML syntax -- run with `ansible-playbook snmp-config.yml`, not Python.

---
- name: Configure SNMP on all routers
  hosts: routers
  gather_facts: no
  tasks:
    - name: Set SNMP community
      ios_config:
        lines:
          - snmp-server community MyReadOnlyString RO

📝 Exercise: Build a Step Runner With Rollback

Write a function run_workflow(steps) where steps is a list of (description, function) tuples. Run each step in order. If any step raises an exception, print which step failed, stop running further steps, and call any '_undo' function already attached to completed steps in REVERSE order (simple rollback). Track completed steps in a list as you go.

code.py

log = []

def provision_vlan():
    log.append("vlan provisioned")

def undo_provision_vlan():
    log.append("vlan rolled back")

def update_firewall():
    log.append("firewall updated")

def undo_update_firewall():
    log.append("firewall rolled back")

def update_dns():
    raise RuntimeError("DNS server unreachable")

steps = [
    ("provision vlan", provision_vlan, undo_provision_vlan),
    ("update firewall", update_firewall, undo_update_firewall),
    ("update dns", update_dns, None),
]

def run_workflow(steps):
    completed = []
    for description, action, undo in steps:
        try:
            action()
            completed.append((description, undo))
        except Exception as error:
            print(f"Step failed: {description} ({error})")
            print("Rolling back completed steps...")
            for description2, undo2 in reversed(completed):
                if undo2:
                    undo2()
            return False
    return True

success = run_workflow(steps)
print("Workflow succeeded" if success else "Workflow failed and rolled back")
print("Log:", log)

Output

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