Re: [Xen-devel] [Notes for xen summit 2018 design session] Process changes: is the 6 monthly release Cadence too short, Security Process, ...

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/07/18 12:18, George Dunlap wrote:
>
>>>    Another potential problems showed up last week: OSSTEST is using the
>>>    Debian servers for doing the basic installation. A change there (e.g.
>>>    a new point release) will block tests. I'd prefer to have a local cache
>>>    of the last known good set of *.deb files to be used especially for the
>>>    branched Xen versions. This would rule out remote problems for releases.
>>>
>>> This is again something which we should definitely look at.
>> This was bad luck.  This kind of update happens about 3-4 times a
>> year.  It does break everything, leading to a delay of a day or two,
>> but the fix is straightforward.
>>
>> Obviously this is not ideal but the solutions are nontrivial.  It is
>> not really possible to "have a local cache of the last known good set
>> of *.deb files" without knowing what that subset should be; that would
>> require an edifice to track what is used, or some manual configuration
>> which would probably break.  Alternatively we could run a complete
>> mirror but that is a *lot* of space and bandwidth, most of which would
>> be unused.
>>
>> I think the right approach is probably to switch from using d-i for
>> host installs, to something like FAI.  That would be faster as well.
>> However that amouns to reengineering the way osstest does host
>> installs; it would also leave us maintaining an additional way to do
>> host installs, since we would still want to be able to *test* d-i
>> operation as a guest.
> What I think would be ideal is a way to take ‘snapshots’ of different states 
> of setup for various hosts and revert to them.  There’s absolutely no reason 
> to do a full install of a host every osstest run, when that install happens 
> 1) before we even install Xen, and 2) should be nearly identical each time.  
> We should be able to install a host, take a snapshot of the “clean” install, 
> then do the build prep, take a snapshot of that, and then simply revert to 
> one or both of those (assuming build requirements haven’t changed in the mean 
> time) whenever necessary.  Re-generating these snapshots once per week per 
> host should be plenty, and sounds like it would massively improve the current 
> throughput.
>
> I’d like to propose the idea also that we try to find a more efficient way of 
> testing guest functionality than doing a guest install.  I understand it’s a 
> natural way to test a reasonable range of functionality, but particularly for 
> Windows guests, my impression is that it’s very slow; there must be a way to 
> make a test that would have similar coverage but be able to be completed with 
> a pre-installed snapshot, in only a few minutes.

We've had similar discussions in XenServer. That idea is superficially
attractive but actually makes things worse, because it now means that
filesystem clone/snapshot is now in the mix of things which can go wrong.

Particularly with OSSTest testing mainline kernels, rather than distro
stable kernels, the chances of finding filesystem bugs grows
substantially, and the complexity of diagnosing an issue is outside of
our area of expertise.

Testing, particularly smoke testing, needs to be 100% reliable to be
useful, and OSSTest is not, is demonstrated across this thread.

The only way to make things better is to improve the reliability. 
Improving reliability means removing all unnecessary complexity, and
replacing any unreliable hardware.

The Xen Project has the money to replace intermittent PDUs (if that is
believed to be the cause of the problem).  What the Xen Project doesn't
have is the time for people to investigate intermittent issues, and what
it can't afford is the current attitude of "oh - that's just OSSTest
being flaky - it will hopefully pass next time".

By far and away the best overall timesaving comes from having all
testing working reliably, at which point OSSTest doesn't need to rerun
tests again in the hope of getting a different answer, and identified
failures are a clear sign to developers that there is a problem which
needs fixing.

~Andrew

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