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On 04/25/2014 03:15 PM, Jay Pipes wrote:

> There are myriad problems with the above user experience and
> implementation. Let me explain them.
>
> 1. The user isn't creating a "server group" when they issue a nova
> server-group-create call. They are creating a policy and calling it a
> group. Cognitive dissonance results from this mismatch.

I actually don't think this is true.  From my perspective they are 
actually creating a group, and then when booting servers they can be 
added into the group.

The group happens to have a policy, it is not only a policy.

> 2. There's no way to add an existing server to this "group".

In the original API there was a way to add existing servers to the 
group.  This didn't make it into the code that was submitted.  It is 
however supported by the instance group db API in nova.

> 3. There's no way to remove members from the group

In the original API there was a way to remove members from the group. 
This didn't make it into the code that was submitted.

> 4. There's no way to manually add members to the server group

Isn't this the same as item 2?

> 5. The act of telling the scheduler to place instances near or away from
> some other instances has been hidden behind the server group API, which
> means that users doing a nova help boot will see a --group option that
> doesn't make much sense, as it doesn't describe the scheduling policy
> activity.

There are many things hidden away that affect server booting...metadata 
matching between host aggregates and flavor extra specs, for instance.

As I understand it, originally the concept of "server groups" was more 
broad.  They supported multiple policies, arbitrary group metadata, etc. 
  The scheduler policy was only one of the things that could be 
associated with a group.  This is why the underlying database structure 
is more complicated than necessary for the current set of supported 
operations.

What we have currently is sort of a "dumbed-down" version but now that 
we have the basic support we can start adding in additional 
functionality as desired.

Chris