[Bug 1037727] Re: support adding region/availability to mirror selection

[Scott Moser]

** Description changed:

+ 
+ === Begin SRU Information ===
+ [Impact]
+  * Currently, local mirror selection is done specifically for EC2 instances
+    in the DataSource code.  cloud-init will select
+   'us-east-1a.ec2.archive.ubuntu.com' as a mirror in EC2.  However, in other
+   clouds, there is no way to get a local mirror selected. 
+ 
+   The change here is to allow mirrors to be specified in configuration based
+   on templates that can include the "availability-zone".  This makes the EC2
+   code generic and allows a cloud provider to have cloud-init select a local
+   mirror simply by presenting 'availability-zone' in the metadata.
+   
+   With this change, if a cloud provider puts 'region-1.mycloud' into their
+   datasource metadata as the availability-zone, cloud-init will select
+   a mirror at 'region-1.mycloud.clouds.archive.ubuntu.com'. By default,
+   Canonical's dns will return that as a wildcard for archive.ubuntu.com,
+   but the information is availble now in the dns request to specify
+   the address of a local mirror.
+ 
+ [Test Case]
+  * This is really a feature backport.  There is no specific bug here.
+    However, the behavior change is easily seen by running an instance on a
+    openstack cloud.  Previously, the mirror selected would be
+    'archive.ubuntu.com'.  With the change in place, the mirror will be:
+    'nova.clouds.archive.ubuntu.com' as by default openstack provides the
+    string 'nova' as the availability-zone.
+ 
+ [Regression Potential]
+  * Mirror selection will change.  It is possible that users relying on
+    the old behavior will have to modify something.
+ 
+ [Other Information]
+  * We want this behavior brought back to 12.04 so that LTS images can "just work"
+    to select a local mirror simply by a change in DNS records.  It will enable
+    large clouds to provide local mirrors easily.
+ 
+ === End SRU Information ===
+ 
  currently, the ec2 datasource has some code that selects the mirror location by looking at the availability-zone.
  I think this is generally a pretty good idea.  I'd like to extend that to other datasources, and not limit to ".ec2.archive.ubuntu.com".
  
  The goal would be to basically check for a mirror at:
-   <availability-zone>[.<cloud>][dns-subdomain]
+   <availability-zone>[.<cloud>][dns-subdomain]
  
  dns subdomain would default to '.cloud.archive.ubuntu.com'.
  
  if the datasource provided the 'cloud' value, we'd use that, but
  otherwise just use availability-zone.
  
  This would fit in with what we're currently doing on ec2, but would extend to others.
  I'd just treat the "cc-direction-[0-9]" availability-zones specially, to know that this is an ec2 one.  Then basically append ".ec2" in that case.

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Title:
  support adding region/availability to mirror selection

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