[Bug 974284] Re: invoking dhclient3 with -1 causes issue if no dhcp server available

[Stéphane Graber]

16:58 < smoser> ie, to safeguard for the power failure case, where 5 minutes wasn't enough, but 5 minutes and 3 seconds would have been.
16:59 < stgraber> so we want dhclient to try for $TIMEOUT, if it gets a lease during that time, background itself and get into a renewal/retry loop, if it doesn't, then ???
16:59 < stgraber> for ??? I tend to prefer failing as I really don't want to run the ifupdown hooks unless we have a working connection
17:00 < stgraber> but you clearly prefer continuing regardless that'll make all the upstart jobs trigger as well as all upstart hooks (even though you don't have network access)


So to make this happen we'd need to patch isc-dhcp-client to add a new parameter (to avoid regressing -1 or the default mode) that essentially only triggers the initial wait for lease part of -1 but not the exit on failure to renew part.

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https://bugs.launchpad.net/bugs/974284

Title:
  invoking dhclient3 with -1 causes issue if no dhcp server available

Status in “isc-dhcp” package in Ubuntu:
  Confirmed

Bug description:
  In bug 838968, we modified ifupdown to invoke dhclient3 with '-1' as a
  parameter [1], and subsequently changed the default timeout of
  dhclient in isc-dhcp3 to from 60 seconds to 300 seconds [2].

  The reason for this is that we now have a reliable "static-networking-
  up" event that can be used for upstart jobs to start on, when static
  networking is up.  Here, static is any networking with an entry in
  /etc/network/interfaces.

  That event is used by cloud-init and other things that depend on
  network.

  The fallout of this is that if for some reason a server (or cloud-
  instance, or anything really), boots and does not obtain a dhcp
  address in 5 minutes, then it will give up forever.  The previous
  behavior is that it would try forever.

  This scenario isn't terribly unrealistic.  A power fail could take out
  a dchp server, cause a fsck, while the server came up 5 minutes before
  the dhcp server was up.

  Issue was originally raised in #openstack-dev by rmk around
  2012-04-05T06:42:19 [3]

  --
  [1] http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/precise/ifupdown/precise/revision/56
  [2] http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/precise/isc-dhcp/precise/revision/32
  [3] http://eavesdrop.openstack.org/irclogs/%23openstack-dev/%23openstack-dev.2012-04-05.log

  Releated bugs:
    * bug 838968: static-network-up event does not wait for interfaces to have an address

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