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AI for OpenStack Difficulty: Advanced ClaudeChatGPT

Magnum Kubernetes Cluster Debug Prompt

Diagnose Magnum K8s cluster creation/scale failures — cluster template, COE driver, Heat stack interaction, node not joining, certificate issues.

Target user
OpenStack operators running Magnum for K8s clusters
Difficulty
Advanced
Tools
Claude, ChatGPT

The prompt

You are a senior OpenStack engineer who has run Magnum-provisioned Kubernetes clusters in production. You can debug failures at the Magnum → Heat → Nova → Neutron → cloud-init layer chain.

I will provide:
- The symptom (cluster creation failed, scaling failed, master/worker not joining, kubectl-not-working)
- `openstack coe cluster show <id>`
- The cluster template (`openstack coe cluster template show`)
- Heat stack status (`openstack stack show` of underlying stack)
- Magnum / Heat logs

Your job:

1. **Understand the stack**:
   - **Magnum** receives cluster create request → spawns a Heat stack
   - **Heat stack** creates Nova instances (master + workers)
   - Instances boot from a glance image + run **cloud-init** to install / configure k8s
   - Magnum monitors cluster status; updates `openstack coe cluster` status
2. **For "cluster create failed"**:
   - Check Heat stack status: `openstack stack show <stack-id>`
   - Resource failures cascade — find first one
   - Common: Nova quota, Neutron port allocation, image issue
3. **For "nodes Booting but not joining cluster"**:
   - Cloud-init failure on the node
   - SSH or console into a worker, check `/var/log/cloud-init.log` and `/var/log/cloud-init-output.log`
   - Common: image missing K8s components, kubeadm join token expired, master API not reachable
4. **For cluster template selection**:
   - `coe = kubernetes`
   - `image_id` — must have K8s components AND cloud-init
   - `network_driver` — flannel, calico, cilium
   - `volume_driver` — cinder for CSI
   - `master_lb_enabled = true` for HA masters
5. **For certificate / kubectl access**:
   - `openstack coe cluster config <id>` downloads kubeconfig
   - Cert authority generated at cluster create
   - Cert rotation: regenerate via Magnum or manually
6. **For scaling**:
   - `openstack coe cluster resize <id> --node-count N`
   - Triggers Heat stack update; new nodes provisioned and joined
   - Failure usually = same root causes as create
7. **For Magnum + Octavia (master LB)**:
   - Master LB enables multi-master HA
   - Failure of LB blocks cluster
8. **For upgrade**:
   - `openstack coe cluster upgrade <id> --cluster-template <new-template>`
   - Rolling replace of masters then workers

Mark DESTRUCTIVE: deleting a cluster (drops all workloads), force-deleting failed cluster (orphans Heat stack), modifying cluster template that's referenced by running clusters (doesn't auto-update).

---

Symptom: [DESCRIBE]
Cluster state:
```
[PASTE `openstack coe cluster show <id>`]
```
Cluster template:
```
[PASTE]
```
Heat stack:
```
[PASTE `openstack stack show <stack-id>`]
```
Cloud-init logs from a failing node:
```
[PASTE]
```

Why this prompt works

Magnum delegates a lot to Heat which delegates to Nova. A failure can be 4 layers deep. This prompt walks the chain.

How to use it

  1. Always check Heat stack first — Magnum reports a generic failure; Heat shows specific.
  2. For cloud-init issues, console-access into the failing node.
  3. Check image — must have all expected components.
  4. For scaling, treat as create of the new nodes.

Useful commands

# Cluster
openstack coe cluster list
openstack coe cluster show <id>
openstack coe cluster template show <template>

# Get kubeconfig
openstack coe cluster config <id> > kubeconfig
export KUBECONFIG=$PWD/kubeconfig
kubectl get nodes

# Heat stack underlying
STACK_ID=$(openstack coe cluster show <cluster-id> -f value -c stack_id)
openstack stack show $STACK_ID
openstack stack event list $STACK_ID --nested-depth 5

# Scaling
openstack coe cluster resize <id> --node-count 5

# Upgrade
openstack coe cluster upgrade <id> --cluster-template <new-template-id>

# Logs (Magnum)
sudo journalctl -u magnum-api -n 100 --no-pager
sudo journalctl -u magnum-conductor -n 100 --no-pager

# Cloud-init on a node (SSH to node)
sudo less /var/log/cloud-init.log
sudo less /var/log/cloud-init-output.log

# K8s side (after node joins)
ssh ubuntu@<master-ip>
sudo systemctl status kubelet
sudo journalctl -u kubelet -n 100

Common findings this catches

  • Heat stack failed at OS::Nova::Server → Nova quota or scheduler issue.
  • All workers boot but don’t join → kubeadm join token expired (15 min default); image issue.
  • Master LB not creating → Octavia not configured or quota.
  • Cluster ACTIVE but kubectl fails → API not reachable from outside (security group, FIP).
  • Cluster template changes ignored → existing clusters not updated; upgrade required.
  • Cinder CSI not working → cluster template lacks volume_driver=cinder or Cinder unhealthy.
  • Scaling down stuck → drain step failed; pods can’t reschedule.

When to escalate

  • Magnum cluster types not supported in your release — engage upstream.
  • Custom Magnum image building — coordinate platform team.
  • Multi-tenant K8s sharing — review isolation; Magnum gives basic.

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