Mark D Horn
5.1 KiB
Network configuration with micro-config-drive (ucd)
Goal of this document
As most cloud-based VMs and containers are deployed in a typical DHCP-enabled environment, and all major Linux distributions are by default configured to use DHCP, there is very little need for users to delve into network configuration details in most cases.
However, in certain environments and more complex uses cases, users may wish to manually configure networking to extend the basic default network setup, or enable extra functionality.
Ucd does not provide any direct functionality to perform network configuration changes, but indirectly it allows the user to do almost everything that the underlying Linux OS allows through 2 simple mechanisms. This document describes those and provides a few basic clues and pointers that demonstrate this functionality.
Introduction
Micro-config-drive does not offer any specific functionality to facilitate network configuration, but offers various generic tools that make this relatively easy to do.
On Linux distributions that use systemd and systemd-networkd,
one can provide simple network configuration files to systemd-networkd
that will instruct it to set up the network as you need.
Other distributions may rely on NetworkManager or other network
configuration services. In general, these will work in a similar way
but may require use of the runcmd directive instead. These
services are not covered by this document.
General Use
As systemd-networkd uses plain text configuration files, we use the
cloud-config directive write_files to output these networkd
configuration files. This can be done by including the following text
in a user data file:
#cloud-config
write_files:
-
path: /etc/systemd/network/<name1>.<network|link|netdev>
content: |
<content of networkd config file>
We can repeat sections like these in case we want to provide multiple configuration files to networkd:
#cloud-config
write_files:
-
path: /etc/systemd/network/<name1>.<network|link|netdev>
content: |
<content of networkd 1 config file>
-
path: /etc/systemd/network/<name2>.<network|link|netdev>
content: |
<content of networkd 2 config file>
Once the proper network configuration files are written out, we may have to restart the network daemon as follows:
#cloud-config
service:
restart: systemd-networkd
Combined, we just append these two parts to have it all written and executed immediately in the order provided:
#cloud-config
write_files:
-
path: /etc/systemd/network/<name1>.<network|link|netdev>
content: |
<content of networkd 1 config file>
-
path: /etc/systemd/network/<name2>.<network|link|netdev>
content: |
<content of networkd 2 config file>
service:
restart: systemd-networkd
Typical Use Cases
Dynamic IP Address
Most distributions provide default networking configurations for DHCP networking, and they usually include a standard DHCP configuration file that largely look as follows:
/usr/lib/systemd/network/80-dhcp.network:
[Match]
Name=en*
[Network]
DHCP=both
[DHCP]
UseDomains=yes
UseMTU=yes
Static IP Address
If one needs to use a static IP address, this can be done as follows:
/etc/systemd/network/enp1s0.network:
[Match]
Name=enp1s0
[Network]
Address=10.0.0.5/24
Gateway=10.0.0.1
Creating a bridged interface
Creating a bridge creates a new virtual netdev, so we have to create
a .netdev file, and declare the bridge interface in it.
/etc/systemd/network/br0.netdev:
[NetDev]
Name=br0
Kind=bridge
Subsequently, we can add any ethernet device to this bridge:
/etc/systemd/network/en.netdev:
[Match]
Name=en*
[Network]
Bridge=br0
And finally, we can instruct the system to get a DHCP lease and assign it to the bridge interface:
/etc/systemd/network/br0.network:
[Match]
Name=br0
[Network]
DHCP=both
All combined, this would look as follows in YAML:
#cloud-config
write_files:
-
path: /etc/systemd/network/br0.netdev
content: |
[NetDev]
Name=br0
Kind=bridge
-
path: /etc/systemd/network/en.netdev
content: |
[Match]
Name=en*
[Network]
Bridge=br0
-
path: /etc/systemd/network/br0.network
content: |
[Match]
Name=br0
[Network]
DHCP=both
service:
restart: systemd-networkd
See Also
The following documentation is not exhaustive and covers a few, more common use cases. Additional documentation is available on several places on the internet that may be useful to the reader.
- https://www.freedesktop.org/software/systemd/man/systemd.network.html
- https://wiki.archlinux.org/index.php/Systemd-networkd
About
This documentation is part of micro-config-drive, see https://github. com/clearlinux/micro-config-drive. For bugs, please e-mail dev@lists.clearlinux.org or visit the https://clearlinux.org/ website. dev@lists.clearlinux.org or visit the https://clearlinux.org/ website. dev@lists.clearlinux.org or visit the https://clearlinux.org/ website.