Two bugs found while rebuilding k8s-node4 (2026-05-26):
1. **runcmd YAML breakage**: `- $${containerd_config_update_command}`
interpolated a multi-line heredoc as bare list-item content. The
trailing lines lost their list-item prefix, breaking cloud-config
parsing. Cloud-init silently fell back to the minimal default
(hostname + package_upgrade only) — kubeadm join, containerd config,
kubelet tuning, iSCSI hardening, swap, ALL skipped. No error visible
in `cloud-init status`.
Fix: wrap the interpolation in `- |` literal block with `indent(4, ...)`.
2. **containerd v2 single-quote mismatch**: `containerd config default`
in v2 writes `config_path = ''` (single quotes), v1 writes `""` (double).
The sed pattern matched only double quotes → silent no-op on fresh
containerd 2.x nodes → registry-mirror hosts.toml ignored → all image
pulls hit upstream registries → DNS-to-MetalLB chicken-and-egg loop.
Fix: match any value with `config_path = .*`.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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