[Bug 1551419] Re: Fix UUID endianness patch breaks cloud-init on Azure

[Dan Watkins]

** Description changed:

  On Azure, cloud-init relies on the system-uuid as based by SMBIOS a
  unique ID for a cloud instance.  If this ID ever changes, then cloud-
  init will attempt to reprovision the VM.
  
  This recent kernel patch in the Ubuntu kernel incorrectly modifies the
  endianness for some SMBIOS fields, which has the effect causing cloud-
  init to think that the system-uuid has changed:
  http://kernel.ubuntu.com/git/ubuntu/ubuntu-
  trusty.git/commit/drivers/firmware?id=3ec24c55be6c543797ba3ee9a227a5631aef607e
  
  cloud-init needs to consider both the reported UUID and the "first three
  fields endian-reversed" UUID as the same, so that users shifting between
  unaffected kernels and affected kernels, or affected kernels and fixed
  kernels do not see their instances reprovisioned.
  
  [Impact]
  
  The impact is that cloud-init attempts to reprovision VMs when they
  reboot to use the new kernel, often causing the customer to lose access
  to their VM.
  
  Once the kernel is fixed, rebooting from an affected kernel to the new
  kernel will have the same effect.
  
  [Test Case]
  
  Failure:
  
  1) Boot an Azure instance using an image with a pre-broken kernel (e.g. b39f27a8b8c64d52b05eac6a62ebad85__Ubuntu-14_04_3-LTS-amd64-server-20160201-en-us-30GB)
  2) Upgrade the kernel and reboot.
  3) SSH to the instance; you will observe that you are prompted to change SSH host keys because cloud-init has run again.
  
  Success (upgrade from not broken->broken):
  
  1) Boot an Azure instance using an image with a pre-broken kernel (e.g. b39f27a8b8c64d52b05eac6a62ebad85__Ubuntu-14_04_3-LTS-amd64-server-20160201-en-us-30GB)
  2) Install the new version of cloud-init.
  3) Upgrade the kernel and reboot.
  4) Observe that you are not prompted when SSHing to instance, as cloud-init has not run again.
+ 5) Make a note of the instance ID in use (i.e. the target of /var/lib/cloud/instance
+ 6) Reboot again.
+ 7) Observe that the instance ID has not changed.
  
  Success (upgrade from broken->fixed):
  1) Boot an Azure instance using an image with a broken kernel (e.g. b39f27a8b8c64d52b05eac6a62ebad85__Ubuntu-14_04_4-LTS-amd64-server-20160222-en-us-30GB)
  2) Install the new version of cloud-init.
  3) Upgrade to the fixed kernel (once it is available) and reboot.
  4) Observe that you are not prompted when SSHing to instance, as cloud-init has not run again.
  
  Success (upgrade from not broken->fixed):
  1) Boot an Azure instance using an image with a pre-broken kernel (e.g. b39f27a8b8c64d52b05eac6a62ebad85__Ubuntu-14_04_3-LTS-amd64-server-20160201-en-us-30GB)
  2) Install the new version of cloud-init.
  3) Upgrade to the fixed kernel (once it is available) and reboot.
  4) Observe that you are not prompted when SSHing to instance, as cloud-init has not run again.
  
  [Regression Potential]
  
  The change is limited to the Azure data source.  It affects how instance
  IDs are determined, but the change does so in a limited way.

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https://bugs.launchpad.net/bugs/1551419

Title:
  Fix UUID endianness patch breaks cloud-init on Azure

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