[Bug 1577844] Re: don't run ifup at .service before networking.service

[Martin Pitt]

** No longer affects: ifupdown (Debian)

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https://bugs.launchpad.net/bugs/1577844

Title:
  don't run ifup at .service before networking.service

Status in cloud-init package in Ubuntu:
  Triaged
Status in ifupdown package in Ubuntu:
  Invalid

Bug description:
  ifup at .service 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 ifup at .service 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 ifup at .service, 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.

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