cloud-init – How Cloud-Init Queries DHCP During Preseed

cloud-initpreseed

We are running a preseeded Ubuntu installation from disk using ubuntu autoinstall (https://ubuntu.com/server/docs/install/autoinstall)

Since upgrading to 20.04.6, we are facing issues when the cloud-init mechanism detects a DHCP server on the network, which crashes the installation.

Is it possible to disable any networking during cloud-init?

Our grub.cfg looks like this:

menuentry "custom install " {
    set gfxpayload=keep
    linux   /casper/vmlinuz quiet autoinstall ds=nocloud\;s=/cdrom/nocloud/ ---
    initrd  /casper/initrd
}

Best Answer

If you'd like to disable cloud-init networking using the kernel cmdline, add:

network-config=disabled

Documentation for disabling network-config in cloud-init can be found at https://cloudinit.readthedocs.io/en/latest/reference/network-config.html#disabling-network-configuration

Related Solutions

Set hostname using cloud-init

Write something like below, change the permission so content will be persistent.

write_files:
  - path: /<your path>/hostname.cfg
    permissions: '<your permission>'
    content: |
      preserve_hostname: true

Other way will be make your host file immutable after first time creation.

Debian 10 cloud-init waiting for DHCP on boot with static network configuration

I encountered the sample problem -- using a static network configuration (NoCloud provider meta-data ENI, or network-config v1/v2) does not disable the DHCP client.

Seems a network config is applied from a template (/etc/network/cloud-interfaces-template) before the cloud-init configuration is written.

auto $INTERFACE
allow-hotplug $INTERFACE

iface $INTERFACE inet dhcp

You can test that this template is the culprit by changing the cloud-image before first start:
(patching the image as changing network config in e.g. bootcmd is too late.)

qemu-nbd --connect=/dev/nbd0 /tmp/debian-10-genericcloud-amd64-20210208-542.qcow2
fdisk /dev/nbd0 -l
mkdir /tmp/nbd
mount /dev/nbd0p1 /tmp/nbd
sed -i 's/dhcp/manual/' /tmp/nbd/etc/network/cloud-interfaces-template
umount /tmp/nbd
rmdir /tmp/nbd
qemu-nbd --disconnect /dev/nbd0

I still need to find a way to apply this change or prevent the use of this template with cloud-init though.

That template seems to be processed by /etc/network/cloud-ifupdown-helper, so that script could be changed or influenced perhaps.

Best Answer

Related Solutions

Set hostname using cloud-init

Debian 10 cloud-init waiting for DHCP on boot with static network configuration

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