Can't get dns to work with cloud-init on debian11

ditzy-olive

I've read this post and also been trying my own research but I just can't get it to work.

https://xcp-ng.org/forum/topic/6777/cloud-init-network-config-not-applying-to-debian-11-6?_=1692953942818

This is my network cloud init configuration

network:
  version: 1
  config:
    - type: physical
      name: eth0
      subnets:
         - type: static
           address: 192.0.2.6/28
           gateway: 192.0.2.1
    - type: nameserver
      interface: eth0
      address:
        - 9.9.9.9
        - 1.1.1.1
      search:
        - example.com
    - type: physical
      name: eth1
      subnets:
         - type: static
           address: 10.10.10.6/24

The result is this file data in /etc/network/interfaces.d/50-cloud-init

auto lo
iface lo inet loopback
    dns-nameservers 9.9.9.9 1.1.1.1
    dns-search example.com

auto eth0
iface eth0 inet static
    address 192.0.2.6/28
    gateway 192.0.2.1

auto eth1
iface eth1 inet static
    address 10.10.10.6/24

how do I get the network in such a way that DNS also works? If I add my nameservers to /etc/resolv.conf everything works.
I'm also a bit confused as why I have eth0 as dhcp on in /etc/network/interfaces but nothing regarding eth1

This cloud-init stuff is driving me bananas!

olivierlambert

This is a Debian question You might check you have the resolvconf package installed, that's where it will check the DNS in the interfaces file and automatically fill the resolv file

ditzy-olive

@olivierlambert it's not that simple I guess. Because I can't install anything without having DNS during the cloud-init
Everything works fine if I use DHCP but this would result in eth0 being my internal network and default GW being via the internal router and eth1 having my public IP.
I want it the other way round

The second solution would be to use DHCP to get everything installed then nuke the whole cloud-init stuff and configure network manually. Bit of a pain I guess.
How are other people dealing with this whole clod-init on debian?

olivierlambert

Why not passing the content of the resolvconf file via Cloudinit?

ditzy-olive

@olivierlambert sure ... how?
I couldn't find out how to do that. Looking into that option right now but if you have some hints I would appreciate it.

olivierlambert

https://cloudinit.readthedocs.io/en/18.5/topics/examples.html#configure-an-instances-resolv-conf

ditzy-olive

@olivierlambert Thanks, just stumbled over this a few minutes ago and tried it, but doesn't work. According to https://www.digitalocean.com/community/tutorials/an-introduction-to-cloud-config-scripting#write-files-to-the-disk

This currently only works for RHEL-based distributions.

But this led me to write_files and this works:

write_files:
  - path: /etc/resolv.conf
    content: |
      domain exmple.com
      search example.com
      nameserver 192.168.20.1

this is the full configuration I use:

#cloud-config
hostname: {name}
timezone: Europe/Vienna
users:
  - default
  - name: johndow
    passwd: ****
    sudo: ALL=(ALL) NOPASSWD:ALL
    groups: users, admin, sudo
    shell: /bin/bash
    lock_passwd: true
    ssh_authorized_keys:
      - ssh-ed25519 AAAA****
write_files:
  - path: /etc/resolv.conf
    content: |
      domain example.com
      search example.com
      nameserver 192.168.20.1
package_update: true
packages:
  - sudo
  - htop
  - vim
  - python
  - tmux
package_upgrade: true
runcmd:
  - sudo reboot

the Network configuration looks like this:

  version: 2
  ethernets:
    eth0:
      match:
        name: eth0
      addresses:
        - 192.168.20.6/28
      gateway4: 192.168.20.1
    eth1:
      match:
        name: eth1
      addresses:
        - 10.10.10.6/24

but now it seems I forgot the MTU but this is a different story, thanks for the hint in the right direction.

olivierlambert

Good news! Keep us posted