[Engine-devel] REST-API: Exposing correlation-ID

[Itamar Heim]

On 05/03/2012 09:49 PM, Ori Liel wrote:
...

>>> Hi Ori,
>>>
>>> Is the intent here to allow correlation between multiple backend actions
>>> initiated from a single restapi call, or an over-arching correlation
>>> across multiple restapi calls?
>>>
>>> If the former, then I'd agree with Yaniv, just generate the ID internally
>>> and return it as a response header.
>>>
>>> If the latter, then allowing it to be optionally set via a request header,
>>> seems more natural to me than a URL parameter because this is additional
>>> out-of-band data that aids in log interpretation, as opposed to something
>>> directly germane to the interaction with the target resource.
>>
>> both.
>> engine auto-generates this if not provided and domain is single command.
>> but client can pass this to see all events or multiple commands running
>> in parallel as part of same single client logical action.
>
> Right, when user passes a correlation ID on the http request, all calls to
> the Backend, that are done in the context of this request, will have this
> correlation-ID (and thus appear in the log as part of the same operation).
>
> But when I think about it, why should the user be involved? If a REST
> action - for example restore-snapshot - involves more than one call to the
> Backend, REST-API (not the user) can decide to always attach a hard-coded,
> descriptive correlation ID to these calls.

true, if API performs multiple actions it should self-generated the ID 
on its own (just like the backend does).

>
> In trying to justify letting the user set the correlation ID, I came up with
> the following scenarios:
> * the user wants to analyze an action in the log, but the server is shared by
> many users. It would be easier to look for "ori's_restore_snapshot" than for
> the generic "restore_snapshot", because maybe other users restored snapshots.
> * tester wants to run the same action 50 times with different parameters, and
> see the actions in the log as: "restore_snapshot_test_1", "restore_snapshot_test_2",
> etc.
>
> So in summary, I think there is some value in letting the user set the value.

another use case - user wants to write their own feature of managing VM 
pools.
user creates a group of VMs via a single action in the UI created on top 
of the REST API.
as far as user is concerned, the 30 VMs created by their action, events, 
and statuses are all part of the same meta-action, so all should have 
the same batch id.

>
> Ori