[Bug 684804] [NEW] cloud-init should fetch image-data as well as user-data

[Alex Bligh]

Public bug reported:

Binary package hint: cloud-init

cloud-init should fetch data specific to the image (and the platform)
prior to fetching user-data, and treat it the same way.

It should be an objective of ubuntu cloud images that they will run on
multiple cloud platforms without customization. As cloud platforms
differ, if the image is not customized, it is necessary for the image to
perform certain platform-specific operations on first boot. These tend
to be image specific too. An example would be to map PV driver disks.

Currently cloud-init sucks down and run a user-data script if supplied. It gets this by default by reading
  http://169.254.169.254/user-data
Cloud platform providers cannot provide data there because there is no agreed format for user-data (i.e. not every user uses the MIME format ubuntu's cloud-init uses), meaning that (a) we would corrupt the user-data blob, and (b) even prepending another MIME part, we'd run into problems with bad MIME etc.

It is suggested that instead cloud-init FIRST gets a user-data script from
   http://169.254.169.254/image-data
or similar. This would be platform specific data (as opposed to instance specific data) that would be run first. This could do platform specific stuff (for instance, change UUID, use custom first password code, disable bits of udev, and so forth).

Added to the end of the URL would be GET parameters describing the
operating system type, release, etc. that could be used to help the
platform provider interpret what they should send down (although this
could form part of the metadata of the image itself, in a situation
where a server is e.g. installed manually on a blank disk it won't be
there).

This should be a pretty trivial addition to cloud-init.

** Affects: cloud-init (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/684804

Title:
  cloud-init should fetch image-data as well as user-data