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

[Stéphane Graber]

** Description changed:

- 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].
+ [rational]
+ A patch was designed to fix this bug back in precise but because of where it was put in debian/patches/00list it was actually being reverted at build time and so never fixing that bug.
+ 
+ In quantal, the reverting code in debian/rules is now gone, so it's been
+ applied ever since the 4.2 merge, so far without hearing any problem
+ with it.
+ 
+ [test case]
+  1) Start dhclient -1 <interface> on a working network
+  2) Unplug the network cable or stop the DHCP server
+  3) Wait for the lease to expire
+  4) Check that dhclient tries to get a new lease and when failing, keeps trying
+ 
+ The original behaviour of -1 would make 4) try just a single time, then
+ give up, causing dhclient to remove all addresses and exit on a machine
+ that was unable to reach its dhcp server for >= expiry.
+ 
+ [regression potential]
+ This change is definitely causing a slight change in behaviour, though based on this bug report and others, it's believe to be the wanted behaviour of -1 for most of our users.
+ The change itself has been applied to quantal without any regression and was tested on 12.04 in the past (before I messed up the ordering in the final upload ...).
+ The code change itself just makes "-1" use the same renewal behaviour as when called without "-1" (but still follows the standard "-1" behaviour for the first request).
+ 
+ 
+ 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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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:
  Fix Released
Status in “isc-dhcp” source package in Precise:
  Confirmed
Status in “isc-dhcp” source package in Quantal:
  Fix Released

Bug description:
  [rational]
  A patch was designed to fix this bug back in precise but because of where it was put in debian/patches/00list it was actually being reverted at build time and so never fixing that bug.

  In quantal, the reverting code in debian/rules is now gone, so it's
  been applied ever since the 4.2 merge, so far without hearing any
  problem with it.

  [test case]
   1) Start dhclient -1 <interface> on a working network
   2) Unplug the network cable or stop the DHCP server
   3) Wait for the lease to expire
   4) Check that dhclient tries to get a new lease and when failing, keeps trying

  The original behaviour of -1 would make 4) try just a single time,
  then give up, causing dhclient to remove all addresses and exit on a
  machine that was unable to reach its dhcp server for >= expiry.

  [regression potential]
  This change is definitely causing a slight change in behaviour, though based on this bug report and others, it's believe to be the wanted behaviour of -1 for most of our users.
  The change itself has been applied to quantal without any regression and was tested on 12.04 in the past (before I messed up the ordering in the final upload ...).
  The code change itself just makes "-1" use the same renewal behaviour as when called without "-1" (but still follows the standard "-1" behaviour for the first request).

  
  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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