---
pattern_id: PAT-008
title: "Ansible default_ipv6 fact missing on fresh VMs → lablabs.rke2 role fails"
category: tooling
severity: medium
status: active
first_observed: 2026-07-21
last_updated: 2026-08-30
related_systems: [rke2-kubernetes]
related_solution_docs:
  - docs/solutions/bug-fixes/2026-07-21-ansible-rke2-default-ipv6-bug.md
related_skills: []
---

# Ansible default_ipv6 fact missing on fresh VMs → lablabs.rke2 role fails

## Symptom

The `lablabs.rke2` Ansible role fails on freshly provisioned VMs with a Jinja2 error:
```
ansible_facts['default_ipv6']['address']
```
The `default_ipv6` fact doesn't exist on VMs without IPv6 configured, causing the
`meta/argument_specs.yml` validation to crash.

## Root Cause

The `lablabs.rke2` role's `meta/argument_specs.yml` references
`ansible_facts['default_ipv6']['address']` with a hardcoded default. On fresh VMs
without IPv6, `ansible_facts['default_ipv6']` is undefined → Jinja2 raises
`UndefinedError`.

A `pre_task` setting `default_ipv6` via `combine()` doesn't help because the
argument_specs validation runs BEFORE pre_tasks — it re-collects facts and
overwrites the pre_task fix.

## Mitigation

Patch `meta/argument_specs.yml` directly in the role:
```yaml
# Replace:
default: "{{ ansible_facts['default_ipv6']['address'] }}"
# With:
default: "{{ ansible_facts.default_ipv6.address | default(None) }}"
```

Or: enable IPv6 on the target VMs (faster workaround, no role patching needed).

## Prevention

- Pin Ansible roles and patch argument_specs when they assume facts that may not exist
- Test roles on fresh VMs without IPv6 before production use
- Consider forking the role with the fix upstream

## Evidence

- Observed during GPU worker provisioning (worker-04/05, Jul 2026)
- Solution doc: `docs/solutions/bug-fixes/2026-07-21-ansible-rke2-default-ipv6-bug.md`
- Session: @session:default/20260721_115501_78b25032