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From Mars Hall <m...@heroku.com>
Subject Re: Remove engine registration
Date Sun, 18 Sep 2016 00:26:09 GMT
Hello folks,

Great to hear about this possibility. I've been working on running PredictionIO on Heroku
https://www.heroku.com

Heroku's 12-factor architecture https://12factor.net prefers "stateless builds" to ensure
that compiled artifacts result in processes which may be cheaply restarted, replaced, and
scaled via process count & size. I imagine this stateless property would be valuable for
others as well.

The fact that `pio build` inserts stateful metadata into a database causes ripples throughout
the lifecycle of PIO engines on Heroku:

* An engine cannot be built for production without the production database available. When
a production database contains PII (personally identifiable information) which has security
compliance requirements, the build system may not be privileged to access that PII data. This
also affects CI (continuous integration/testing), where engines would need to be rebuilt in
production, defeating assurances CI is supposed to provide.

* The build artifacts cannot be reliably reused. "Slugs" at Heroku are intended to be stateless,
so that you can rollback to a previous version during the lifetime of an app. With `pio build`
causing database side-effects, there's a greater-than-zero probability of slug-to-metadata
inconsistencies eventually surfacing in a long-running system.


From my user-perspective, a few changes to the CLI would fix it:

1. add a "skip registration" option, `pio build --without-engine-registration`
2. a new command `pio app register` that could be run separately in the built engine (before
training)

Alas, I do not know PredictionIO internals, so I can only offer a suggestion for how this
might be solved.


Donald, one specific note,

Regarding "No automatic version matching of PIO binary distribution and artifacts version
used in the engine template":

The Heroku slug contains the PredictionIO binary distribution used to build the engine, so
there's never a version matching issue. I guess some systems might deploy only the engine
artifacts to production where a pre-existing PIO binary is available, but that seems like
a risky practice for long-running systems.


Thanks for listening,

*Mars Hall
Customer Facing Architect
Salesforce App Cloud / Heroku
San Francisco, California

> On Sep 16, 2016, at 10:42, Donald Szeto <donald@apache.org> wrote:
> 
> Hi all,
> 
> I want to start the discussion of removing engine registration. How many people actually
take advantage of being able to run pio commands everywhere outside of an engine template
directory? This will be a nontrivial change on the operational side so I want to gauge the
potential impact to existing users.
> 
> Pros:
> - Stateless build. This would work well with many PaaS.
> - Eliminate the "pio build" command once and for all.
> - Ability to use your own build system, i.e. Maven, Ant, Gradle, etc.
> - Potentially better experience with IDE since engine templates no longer depends on
an SBT plugin.
> 
> Cons:
> - Inability to run pio engine training and deployment commands outside of engine template
directory.
> - No automatic version matching of PIO binary distribution and artifacts version used
in the engine template.
> - A less unified user experience: from pio-build-train-deploy to build, then pio-train-deploy.
> 
> Regards,
> Donald


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