[nova] Thoughts on exposing exception type to non-admins in instance action event

Matt Riedemann mriedemos at gmail.com
Thu Nov 14 13:58:17 UTC 2019

On 11/13/2019 2:38 PM, Eric Fried wrote:
> Okay, are we going to have a document that maps exception classes to
> these explanations and recovery actions? Which we then have to maintain
> as the code changes? Or are they expected to look through code (without
> a stack trace)?


> I'm not against the idea, just playing devil's advocate. Sylvain seems
> to have a use case, so great.

Yeah I know. Like I said in the original email, just having the 
exception type might not be very useful to an end user. That's almost 
like just showing an error code that is then used by support staff. If 
we do expose the details as the formatted exception message, like we do 
for faults, then I think it would be more useful to end users, but then 
you also run into the same issues as we have for fault messages that 
maybe leak too much detail [1]. However, with the way I was thinking 
about doing this, the instance action code would use the same utility 
method that generates the fault message so if we fix [1] for faults it's 
also fixed for instance actions automatically.

If I get the time this week I'll WIP something together that does what 
I'm thinking as a proof of concept, likely without the microversion 
stuff just since that's unnecessary overhead for a PoC.

> As an alternative, have we considered a mechanism whereby we could, in
> appropriate code paths, provide some text that's expressly intended for
> the end user to see? Maybe it's a new user_message field on
> NovaException which, if present, gets percolated up to a new field
> similar to the one you suggested.

I think that likely becomes as whack-a-mole to contain as documenting 
all of the different types of errors.

[1] https://bugs.launchpad.net/nova/+bug/1851587




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