notes: kubevirt networking fix for Ubuntu

Signed-off-by: Xe Iaso <me@xeiaso.net>

1 files changed, 45 insertions, 0 deletions

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+---
+title: "Fixing Kubevirt networking not working on reboot"
+date: 2024-09-26
+desc: "Turns out randomizing the MAC address on boot is a bad idea"
+---
+
+When you use Ubuntu on Kubevirt like I do, rebooting a VM or manually rescheduling pods means that the MAC address in the VM changes. This makes Ubuntu's netplan very unhappy and will result in your VM not acquiring an IP address over DHCP. This is not good for uptime.
+
+After searching the GitHub issue tracker, I found [this comment](https://github.com/kubevirt/kubevirt/issues/1646#issuecomment-433262034) from 2018 that suggested adding this netplan configuration file to the VM:
+
+```yaml
+network:
+  version: 2
+  ethernets:
+    id0:
+      dhcp4: true
+      match:
+        name: enp*
+```
+
+This does the trick, so my minimal cloud-init config for Ubuntu on Kubevirt VM looks like this:
+
+```yaml
+#cloud-config
+hostname: noble
+ssh_pwauth: True
+disable_root: false
+
+write_files:
+  - encoding: b64
+  content: bmV0d29yazoKICB2ZXJzaW9uOiAyCiAgZXRoZXJuZXRzOgogICAgaWQwOgogICAgICBkaGNwNDogdHJ1ZQogICAgICBtYXRjaDoKICAgICAgICBuYW1lOiBlbnAqCg==
+  owner: root:root
+  path: /etc/netplan/99-net-fix.yaml
+  permissions: '0644'
+
+users:
+  - name: xe
+    groups: [ wheel ]
+    sudo: [ "ALL=(ALL) NOPASSWD:ALL" ]
+    shell: /bin/bash
+    ssh_import_id:
+      - gh:xe
+```
+
+I've done reboot testing with my virtual machines and this seems to work consistently enough.