[enhancement]: Disable IPv4 to setup a IPv6 only network by cloud-init

ruishuangvmw commented 4 weeks ago

Hi, Can I disable IPv4 and configure an IPv6-only network on some mainstream Linux by cloud-init? My datastore uses https://cloudinit.readthedocs.io/en/latest/reference/network-config-format-v1.html format config file.

Subnet types are one of the following:
dhcp4: Configure this interface with IPv4 dhcp.
dhcp: Alias for dhcp4.
dhcp6: Configure this interface with IPv6 dhcp.
static: Configure this interface with a static IPv4.
static6: Configure this interface with a static IPv6.
ipv6_dhcpv6-stateful: Configure this interface with dhcp6.
ipv6_dhcpv6-stateless: Configure this interface with SLAAC and DHCP.
ipv6_slaac: Configure address with SLAAC.

The above subnet type has no disable ipv4 options currently. And from the testing, the nic was configured either DHCP or static. Thanks,

blackboxsw commented 2 weeks ago

Thank you @ruishuangvmw for filing this bug and making cloud-init better. I believe the absence of dhcp4/static config config type would be enough to prevent IPV4 configuration in the target Linux image on boot.

This details of this bug are a bit vague and I'm not quite certain from the bug where things are not working for you.

Provided those types you mentioned in the bug and our docs, we can see cloud-init rendering the appropriate network config content for the supported network backends: ENI (/etc/network/interfaces), sysconfig, netplan and network manager.

Here are some example network config files that represent configuration which does not setup IPV4-based config.

static ipv6 network v1 config

cat > static-ipv6.yaml <<EOF
network:
  config:
    - mac_address: aa:12:bc:34:ee:ac
      name: eno3
      subnets:
      - address: fd00::12/64
        dns_nameservers: ['fd00:2::15']
        gateway: fd00::1
        ipv6: true
        routes:
        - netmask: '32'
          network: 'fd00:12::'
          gateway: 'fd00::2'
        type: static6
      type: physical
  version: 1
EOF

IPv6 DHCP network v1 config

network:
  config:
    - mac_address: aa:12:bc:34:ee:ac
      name: eno3
      subnets:
      - type: dhcp6
      type: physical
  version: 1

To check the network config files that cloud-init would generate without having to boot a machine you can run the net-convert command either on a system which has cloud-init installed, or from a clone of our cloud-init repo:

# on a system with cloud-init pre-installed render example netplan configuration for iPV6 static config file ./out.d/etc/netplan 50-cloud-init.yaml:
cloud-init devel net-convert --kind=yaml --network-data=ipv6.yaml --output-kind=netplan --directory=out.d --distro debian

# In a cloned cloud-init source repository, render example dhcp6-only config sysconfig files in out.d/etc/network/sysconfi for RedHat/suse systems:
git clone https://github.com/canonical/cloud-init.git
cd cloud-init
PYTHONPATH=. python3 -m cloud-init.cmd.main devel net-convert --kind=yaml --network-data=dhcp6.yaml --output-kind=sysconfig --directory=out.d --distro rhel

If a specific rendered network config does not work for your desired Linux distribution and/or desired network backend (network-manager, networkd, sysconfig, networkd. netplan, eni) please add the details of that source network config v1 and the problematic --output-kind that is causing issues in your environment.

I'll make this issue as incomplete until we have more specifics to help us understand what isn't working in your environment.

Some things to validate on a deployed instance:

[ -f run/cloud-init/network-config.json] && echo /run/cloud-init/network-config.json
grep "Applying network" /var/log/cloud-init.log
ip -a
ip route
ip -6 route

ruishuangvmw commented 2 weeks ago

Thank @blackboxsw for your reply. Great! This v1 config work on my testbed, and it could disable IPv4 network on RHEL, Debian and SLES OS. I will close this issue since I think cloud-init's existing features already meet our requirements. Thanks again

canonical / cloud-init