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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Option A can be made usable provided you do the following:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l3 level1 lfo8"><![if !supportLists]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Add an endpoint for determining whether or not the current service supports optional feature X.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l3 level1 lfo8"><![if !supportLists]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">For each optional feature of the API, clearly document that the feature is optional, and name the feature it is part of.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l3 level1 lfo8"><![if !supportLists]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><span style="mso-list:Ignore">3.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">If the optional feature is defined within the core Marconi specification, require implementations to return a 501 for affected URIs if the feature
is not supported (this is in addition to, not in place of, item #1 above).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">A description of some key documentation elements I am looking for when a service includes optional functionality is listed under the heading “Conceptual Grouping”
in the following document:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><a href="https://github.com/sharwell/openstack.net/wiki/The-JSON-Checklist">https://github.com/sharwell/openstack.net/wiki/The-JSON-Checklist</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Thank you,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Sam Harwell<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Kurt Griffiths [mailto:kurt.griffiths@rackspace.com]
<br>
<b>Sent:</b> Monday, June 09, 2014 2:31 PM<br>
<b>To:</b> OpenStack Dev<br>
<b>Subject:</b> [openstack-dev] [marconi] Reconsidering the unified API model<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Folks, this may be a bit of a bombshell, but I think we have been dancing around the issue for a while now and we need to address it head on. Let me start with
some background.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Back when we started designing the Marconi API, we knew that we wanted to support several messaging patterns. We could do that using a unified queue resource,
combining both task distribution and feed semantics. Or we could create disjoint resources in the API, or even create two separate services altogether, one each for the two semantic groups.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">The decision was made to go with a unified API for these reasons:<o:p></o:p></span></p>
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<ul type="disc">
<li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l7 level1 lfo1">
<span style="font-size:10.5pt;font-family:"Calibri","sans-serif"">It would afford hybrid patterns, such as auditing or diagnosing a task distribution queue<o:p></o:p></span></li><li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l7 level1 lfo1">
<span style="font-size:10.5pt;font-family:"Calibri","sans-serif"">Once you implement guaranteed delivery for a message feed over HTTP, implementing task distribution is a relatively straightforward addition. If you want both types of semantics, you don’t necessarily
gain anything by implementing them separately.<o:p></o:p></span></li></ul>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Lately we have been talking about writing drivers for traditional message brokers that will not be able to support the message feeds part of the API. I’ve started
to think that having a huge part of the API that may or may not “work”, depending on how Marconi is deployed, is not a good story for users, esp. in light of the push to make different clouds more interoperable. <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Therefore, I think we have a very big decision to make here as a team and a community. I see three options right now. I’ve listed several—but by no means conclusive—pros
and cons for each, as well as some counterpoints, based on past discussions.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Option A.</span></b><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black"> Allow drivers to only implement part of the API<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">For:<o:p></o:p></span></p>
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<ul type="disc">
<li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo2">
<span style="font-size:10.5pt;font-family:"Calibri","sans-serif"">Allows for a wider variety of backends. (counter: may create subtle differences in behavior between deployments)<o:p></o:p></span></li><li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo2">
<span style="font-size:10.5pt;font-family:"Calibri","sans-serif"">May provide opportunities for tuning deployments for specific workloads<o:p></o:p></span></li></ul>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Against:<o:p></o:p></span></p>
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<ul type="disc">
<li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l4 level1 lfo3">
<span style="font-size:10.5pt;font-family:"Calibri","sans-serif"">Makes it hard for users to create applications that work across multiple clouds, since critical functionality may or may not be available in a given deployment. (counter: how many users need
cross-cloud compatibility? Can they degrade gracefully?)<o:p></o:p></span></li></ul>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Option B.
</span></b><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Split the service in two. Different APIs, different services. One would be message feeds, while the other would be something akin to Amazon’s SQS.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">For:<o:p></o:p></span></p>
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<ul type="disc">
<li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo4">
<span style="font-size:10.5pt;font-family:"Calibri","sans-serif"">Same as Option A, plus creates a clean line of functionality for deployment (deploy one service or the other, or both, with clear expectations of what messaging patterns are supported in any
case).<o:p></o:p></span></li></ul>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Against:<o:p></o:p></span></p>
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<ul type="disc">
<li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l2 level1 lfo5">
<span style="font-size:10.5pt;font-family:"Calibri","sans-serif"">Removes support for hybrid messaging patterns (counter: how useful are such patterns in the first place?)<o:p></o:p></span></li><li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l2 level1 lfo5">
<span style="font-size:10.5pt;font-family:"Calibri","sans-serif"">Operators now have two services to deploy and support, rather than just one (counter: can scale them independently, perhaps leading to gains in efficiency)<o:p></o:p></span></li></ul>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Option C.</span></b><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black"> Require every backend to support the entirety of the API
as it now stands. <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">For:<o:p></o:p></span></p>
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<ul type="disc">
<li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l5 level1 lfo6">
<span style="font-size:10.5pt;font-family:"Calibri","sans-serif"">Least disruptive in terms of the current API design and implementation<o:p></o:p></span></li><li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l5 level1 lfo6">
<span style="font-size:10.5pt;font-family:"Calibri","sans-serif"">Affords a wider variety of messaging patterns (counter: YAGNI?)<o:p></o:p></span></li><li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l5 level1 lfo6">
<span style="font-size:10.5pt;font-family:"Calibri","sans-serif"">Reuses code in drivers and API between feed and task distribution operations (counter: there may be ways to continue sharing some code if the API is split)<o:p></o:p></span></li></ul>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Against:<o:p></o:p></span></p>
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<ul type="disc">
<li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l6 level1 lfo7">
<span style="font-size:10.5pt;font-family:"Calibri","sans-serif"">Requires operators to deploy a NoSQL cluster (counter: many operators are comfortable with NoSQL today)<o:p></o:p></span></li><li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l6 level1 lfo7">
<span style="font-size:10.5pt;font-family:"Calibri","sans-serif"">Currently requires MongoDB, which is AGPL (counter: a Redis driver is under development)<o:p></o:p></span></li><li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l6 level1 lfo7">
<span style="font-size:10.5pt;font-family:"Calibri","sans-serif"">A unified API is hard to tune for performance (counter: Redis driver should be able to handle high-throughput use cases, TBD)<o:p></o:p></span></li></ul>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">I’d love to get everyone’s thoughts on these options; let's brainstorm for a bit, then we can home in on the option that makes the most sense. We may need to
do some POCs or experiments to get enough information to make a good decision.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">@kgriffs<o:p></o:p></span></p>
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