Network Configuration

  • Default Behavior
  • Disabling Network Configuration
  • Fallback Networking
  • Network Configuration Sources
  • Network Configuration Outputs
  • Network Output Policy
  • Network Configuration Tools
  • Examples

Default Behavior

Cloud-init ‘s searches for network configuration in order of increasing precedence; each item overriding the previous.

Datasource

For example, OpenStack may provide network config in the MetaData Service.

System Config

A network: entry in /etc/cloud/cloud.cfg.d/* configuration files.

Kernel Command Line

ip= or network-config=<YAML config string>

User-data cannot change an instance’s network configuration. In the absense of network configuration in any of the above sources , Cloud-init will write out a network configuration that will issue a DHCP request on a “first” network interface.

Disabling Network Configuration

Users may disable Cloud-init ‘s network configuration capability and rely on other methods, such as embedded configuration or other customizations.

Cloud-init supports the following methods for disabling cloud-init.

Kernel Command Line

Cloud-init will check for a parameter network-config and the value is expected to be YAML string in the Networking Config Version 1 format. The YAML string may optionally be Base64 encoded, and optionally compressed with gzip.

Example disabling kernel command line entry:

network-config={config: disabled}

cloud config

In the combined cloud-init configuration dictionary.

network:
  config: disabled

If Cloud-init ‘s networking config has not been disabled, and no other network information is found, then it will proceed to generate a fallback networking configuration.

Fallback Network Configuration

Cloud-init will attempt to determine which of any attached network devices is most likely to have a connection and then generate a network configuration to issue a DHCP request on that interface.

Cloud-init runs during early boot and does not expect composed network devices (such as Bridges) to be available. Cloud-init does not consider the following interface devices as likely ‘first’ network interfaces for fallback configuration; they are filtered out from being selected.

  • loopback: name=lo
  • Virtual Ethernet: name=veth*
  • Software Bridges: type=bridge
  • Software VLANs: type=vlan

Cloud-init will prefer network interfaces that indicate they are connected via the Linux carrier flag being set. If no interfaces are marked connected, then all unfiltered interfaces are potential connections.

Of the potential interfaces, Cloud-init will attempt to pick the “right” interface given the information it has available.

Finally after selecting the “right” interface, a configuration is generated and applied to the system.

Network Configuration Sources

Cloud-init accepts a number of different network configuration formats in support of different cloud substrates. The Datasource for these clouds in Cloud-init will detect and consume Datasource-specific network configuration formats for use when writing an instance’s network configuration.

The following Datasources optionally provide network configuration:

For more information on network configuration formats

Network Configuration Outputs

Cloud-init converts various forms of user supplied or automatically generated configuration into an internal network configuration state. From this state Cloud-init delegates rendering of the configuration to Distro supported formats. The following renderers are supported in cloud-init:

  • ENI

/etc/network/interfaces or ENI is supported by the ifupdown package found in Ubuntu and Debian.

  • Netplan

Since Ubuntu 16.10, codename Yakkety, the netplan project has been an optional network configuration tool which consumes Networking Config Version 2 input and renders network configuration for supported backends such as systemd-networkd and NetworkManager.

  • Sysconfig

Sysconfig format is used by RHEL, CentOS, Fedora and other derivatives.

Network Output Policy

The default policy for selecting a network renderer in order of preference is as follows:

  • ENI
  • Sysconfig
  • Netplan

When applying the policy, Cloud-init checks if the current instance has the correct binaries and paths to support the renderer. The first renderer that can be used is selected. Users may override the network renderer policy by supplying an updated configuration in cloud-config.

system_info:
  network:
    renderers: ['netplan', 'eni', 'sysconfig']

Network Configuration Tools

Cloud-init contains one tool used to test input/output conversion between formats. The tools/net-convert.py in the Cloud-init source repository is helpful for examining expected output for a given input format.

CLI Interface :

% tools/net-convert.py --help
usage: net-convert.py [-h] --network-data PATH --kind
                      {eni,network_data.json,yaml} -d PATH [-m name,mac]
                      --output-kind {eni,netplan,sysconfig}

optional arguments:
  -h, --help            show this help message and exit
  --network-data PATH, -p PATH
  --kind {eni,network_data.json,yaml}, -k {eni,network_data.json,yaml}
  -d PATH, --directory PATH
                        directory to place output in
  -m name,mac, --mac name,mac
                        interface name to mac mapping
  --output-kind {eni,netplan,sysconfig}, -ok {eni,netplan,sysconfig}

Example output convertion V2 to sysconfig:

% tools/net-convert.py --network-data v2.yaml --kind yaml \
    --output-kind sysconfig -d target
% cat target/etc/sysconfig/network-scripts/ifcfg-eth*
# Created by cloud-init on instance boot automatically, do not edit.
#
BOOTPROTO=static
DEVICE=eth7
IPADDR=192.168.1.5/255.255.255.0
NM_CONTROLLED=no
ONBOOT=yes
TYPE=Ethernet
USERCTL=no
# Created by cloud-init on instance boot automatically, do not edit.
#
BOOTPROTO=dhcp
DEVICE=eth9
NM_CONTROLLED=no
ONBOOT=yes
TYPE=Ethernet
USERCTL=no