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On 08/27/2015 09:38 PM, Ben Swartzlander wrote:
> Manila recently implemented microversions, copying the implementation
> from Nova. I really like the feature! However I noticed that it's legal
> for clients to transmit "latest" instead of a real version number.
>
> THIS IS A TERRIBLE IDEA!
>
> I recommend removing support for "latest" and forcing clients to request
> a specific version (or accept the default).

I think "latest" is needed for integration testing. Otherwise you have 
to update your tests each time new version is introduced.

>
> Allowing clients to request the "latest" microversion guarantees
> undefined (and likely broken) behavior* in every situation where a
> client talks to a server that is newer than it.
>
> Every client can only understand past and present API implementation,
> not future implementations. Transmitting "latest" implies an assumption
> that the future is not so different from the present. This assumption
> about future behavior is precisely what we don't want clients to make,
> because it prevents forward progress. One of the main reasons
> microversions is a valuable feature is because it allows forward
> progress by letting us make major changes without breaking old clients.
>
> If clients are allowed to assume that nothing will change too much in
> the future (which is what asking for "latest" implies) then the server
> will be right back in the situation it was trying to get out of -- it
> can never change any API in a way that might break old clients.
>
> I can think of no situation where transmitting "latest" is better than
> transmitting the highest version that existed at the time the client was
> written.
>
> -Ben Swartzlander
>
> * Undefined/broken behavior unless the server restricts itself to never
> making any backward-compatiblity-breaking change of any kind.
>
>
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