[openstack-dev] Continuous deployment - significant process change

Russell Bryant rbryant at redhat.com
Mon Apr 29 22:48:00 UTC 2013

On 04/29/2013 06:39 PM, Sullivan, Jon Paul wrote:
>> -----Original Message-----
>> From: Russell Bryant [mailto:rbryant at redhat.com]
>> Sent: 29 April 2013 22:51
>> To: openstack-dev at lists.openstack.org
>> Subject: Re: [openstack-dev] Continuous deployment - significant process
>> change
>> On 04/29/2013 05:04 PM, Robert Collins wrote:
>>> We had a process track session about bringing in upstream continuous
>>> deployment for openstack.
>>> https://etherpad.openstack.org/HavanaContinuousDeployment
>>> I suspect that while the session was good with both deployer and
>>> distributor attendees, we need to do more to make it happen, as it
>>> impinges on review / testing / backwards compat requirements for every
>>> project.
>>> Note that CD doesn't require no-downtime deployments, CD is about
>>> being able to adopt *any arbitrary revision of trunk* at *any point in
>>> time*. The engineering required to do deployments without disruption
>>> is beneficial to both CD and per-release deployments.
>>> Here are the key takeaways we came up with:
>>>  * No more big landings [except the purely mechanical]. Set a hard
>>> limit - maybe 500 lines of diff. Big landings are more risky per line
>>> of diff than small ones due to reviewer cognitive overhead - reviewers
>>> get non-linearly less effective the larger the review.
>> I don't think we can set a # of lines that always makes sense.  However,
>> I feel like in Nova we already do a nice job of pushing back hard on
>> large patches in favor of breaking them up into a reasonable patch
>> series.
>> https://wiki.openstack.org/wiki/GitCommitMessages
>> So, at least for Nova, this is business as usual.
>>>  * CD can be done many ways; we need to gate the *specific* ways that
>>> upstream adopts, as soon as possible. Thats a -infra thing, and there
>>> are already discussions on it. We don't need to support *every
>>> possible config for CD*. Organisations interested in a particular
>>> configuration(s) will need to contribute resources to permit
>>> gate-quality checks of those configurations.
>>>  * No more cramming: when a freeze is happening, anything that is
>>> 'land this for the release' has to be pushed back on -really hard-. If
>>> its not ready, it's not ready.
>>>  * -never- choose to break something that is neither experimental nor
>>> deprecated since the last release. If an accident happens, correct it
>>> as quickly as possible.
>>>  * Land features disabled by default. Such disabled features are
>>> experimental and we don't need to be so careful - we can in fact
>>> remove them entirely if they turn out to be bad idea - when they
>>> become supported (individual teams can define this we think) they
>>> can't be broken again though: they are now part of the product.
>>>  * 'To break' means just that - it could be an exception, it could be
>>> a massive jump in DB utilisation, or latency. Whatever our criteria
>>> are for 'fit for use', breaking something stops it being fit for use
>>> in *existing deployed environments*.
>> Most of this seems good.  It seems as if there's tension between:
>> 1) Ensuring utmost quality so you can deploy any revision
>> and
>> 2) Being less careful with some new features and justifying it by having
>> them disabled by default.
>> I don't see the value in this disabled-by-default thing.  Another one of
>> your points stresses the fact that if something's not ready, it's not
>> ready, which I definitely agree with.
> I think this article gives a good argument for "disabled-by-default".  It is a valid way to retain small commits to the code base which are easily reviewable whilst enabling developers to continue development on the feature in a safe way.  Without this you may lose the ability to keep commits small enough to be digestible to reviewers.
> http://rc3.org/2013/03/03/dont-get-stuck/

I think you can develop a feature in its entirety with a series of
reasonably sized changes with a well designed patch set.

Once code gets in to the tree, it becomes a burden on the project to
maintain that code, even if disabled by default.  If your feature isn't
done, I don't want it in the tree.

Russell Bryant

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