Turns out this was all just an illusion. [email protected] already has
"After=network-pre.target", i. e. is actual execution will already be
deferred until after network-pre.target. cloud-init-local.service is
Before=network-pre.target, so the effect of any hotplug event will sort
correctly.
I added a "ExecStart=/bin/sleep 5" to cloud-init-local.service, and this
shows that network-pre.target and ifup@ correctly blocks:
May 04 14:57:05 autopkgtest cloud-init[336]: [CLOUDINIT] stages.py[INFO]:
network config is disabled by /var/lib/cloud/data/upgraded-network
May 04 14:57:05 autopkgtest cloud-init[336]: Cloud-init v. 0.7.7 running
'init-local' at Wed, 04 May 2016 12:57:04 +0000. Up 3.64 seconds.
May 04 14:57:10 autopkgtest systemd[1]: Started Initial cloud-init job
(pre-networking).
May 04 14:57:10 autopkgtest systemd[1]: Reached target Network (Pre).
May 04 14:57:10 autopkgtest systemd[1]: Starting Raise network interfaces...
May 04 14:57:11 autopkgtest systemd[1]: Started ifup for ens3.
So there is nothing to fix in ifupdown, and it should be safe to drop
all the hackery in cloud-init: /run/cloud-init/network-config-ready from
cloud-init-local.service, the whole cloud-init-wait, and
/lib/udev/rules.d/79-cloud-init-net-wait.rules.
** Changed in: ifupdown (Ubuntu)
Status: In Progress => Invalid
** Changed in: cloud-init (Ubuntu)
Status: New => Triaged
** Summary changed:
- don't run [email protected] before networking.service
+ Drop unnecessary blocking of all net udev rules
** Description changed:
+ cloud-inits networking setup currently jumps through a lot of bad hoops
+ to make sure that ifup@ does not run until after cloud-init-
+ local.service. This includes blocking udev rules for an indefinite time,
+ which is racy, a potential deadlock, and highly non-elegant.
+
+ This is also not necessary: while ifupdown's net udev rule certainly can
+ fire before cloud-init-local, it only asynchronously starts
+ [email protected] which will be deferred until after network-pre.target and
+ thus after cloud-init-local.service.
+
+ -------
+ Original description, which turned out to be completely false and just us
being misled:
+
[email protected] can (and often does) run for a particular interface before
networking.service runs. This is brittle as during early boot ifup is
prone to fail: / might still be read-only, /var might not yet exist or
be writable, dhclient-enter-hooks.d/ or if-up.d/ hooks might silently
fail, etc. It is also unnecessary as networking.service will bring up
all "auto" and all present "allow-hotplug" interfaces anyway, and it
runs at the right time.
We should make either 80-ifupdown.rules or [email protected] ignore events
until networking.service is active, or wait until after it has run
(slower, but avoids race conditions when hotplug events happen while
networking.service is running). Thus we need to add
After=networking.service to [email protected], so that this only does stuff
after doing the "coldplug" configuration.
This also affects cloud-init's setup of networking: this currently jumps
through a lot of bad hoops to make sure that ifup@ does not run until
after cloud-init-local.service. This includes blocking udev rules for an
indefinite time, which is racy, a potential deadlock, and highly non-
elegant.
https://bugs.debian.org/752919 is related to this issue.
** Changed in: cloud-init (Ubuntu)
Assignee: (unassigned) => Scott Moser (smoser)
** Changed in: ifupdown (Ubuntu)
Assignee: Martin Pitt (pitti) => (unassigned)
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https://bugs.launchpad.net/bugs/1577844
Title:
Drop unnecessary blocking of all net udev rules
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