Netplan does not support any pre/post-up/down hooks on its own, but is
referring to a mapping table from ifupdown to its two backend renderers
“NetworkManager-dispatcher” and “networkd-dispatcher”, which we are
currently updating to better explain the details, pitfalls and
differences: https://github.com/canonical/netplan.io/pull/245
It’s not a 1:1 mapping, as the three hook dispatchers behave slightly
differently, especially wrt. Networkd-dispatcher being a pure listener, running
hook scripts asynchronous, whereas ENI and NM handle the hook scripts natively
and allow them to interject the interface configuration process.
Also, systemd-networkd does not keep an internal state (in contrast to
ENI & NM) but relies on the kernel’s netlink state, thus uses different
stages and cannot implement a “pre-down” hook at all.
Unfortunately, this is the best we can do for now, without requiring
upstream changes to systemd, inroducing a possibility to block network
configuration, controlled by external hooks, which the systemd devs want
to avoid, due to performance concerns.
** Changed in: netplan
Status: New => Fix Committed
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https://bugs.launchpad.net/bugs/1664818
Title:
Not possible to render pre-up, pre-down, post-up, or post-down
snippets
Status in netplan:
Fix Committed
Status in systemd package in Ubuntu:
Triaged
Bug description:
Many configurations require scripts to run before or after an
interface comes up or down.
Example: I had a situation where I needed to render a post-up script
to monitor an interface with ifupdown (and with the interface set to
manual mode, because if the link was down I didn't want to require
DHCP to run before the system continued booting). This is similar to
what NetworkManager does in order to launch (or kill) a DHCP client.
Other use cases involve setting up custom routes (such as when complex
logic involving metrics or source routing is required) or anything
else the designers of the netplan rendering engine didn't think of,
such as invoking workarounds or special settings required for a
particular NIC or environment, iptables rules that should be added or
removed, etc.
A follow-on issue is, it should be possible to ask that custom scripts
run if the *link* is detected to come up or down. But I'll be happy if
netplan first can simply replicate the custom-script-invoking behavior
of ifupdown.
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