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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Ilya,<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'>Both designs are valid (whether the LBaaS plugin implements a uniform asynchronous model, or whether to leave it to each vendor to decide whether their driver is synchronous or not), and I’m fine with choosing the one you described. I have a few questions on it.<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'>In that setup, I’m assuming we will have 2 processes: The Quantum service process and the Agent process. The two communicate thru message queues. No vendor-specific code will be in the Quantum service process. The Agent process is the one that has all the vendors drivers loaded in. <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'>Where are you planning for the agent process to run? On the same host as the Quantum service process? On a separate host? On the device? Imagine in the same agent, you have a case where one driver assumes it is on the same machine as the device (HA-Proxy?), while another driver uses a remote protocol to configure the device (the agent cannot run on the device as the device is a sealed appliance), where does the agent run in this case?<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'>The other question I have is on the LBaaS plugin workflow that you described in this diagram: </span><a href="http://wiki.openstack.org/Quantum/LBaaS/Architecture/ConcurrentRequests">http://wiki.openstack.org/Quantum/LBaaS/Architecture/ConcurrentRequests</a>. <span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Here it seems that we are returning a response to the user even before we update the database. So, this could mean that if the Quantum service crashes before updating the database, we would have lost all details of the request, even though we have returned a resource ID, and a “PENDING_CREATE” status to the user. So, when the user queries the service (after it has restarted) to get the status of the creation, the resource wouldn’t even exist since it has never been saved to the DB. What do you think of updating the DB before returning the response to the user?</span><o:p></o:p></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'>Thanks<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Youcef<o:p></o:p></span></p><p class=MsoNormal><a name="_MailEndCompose"><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></a></p><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"'> Ilya Shakhat [mailto:ishakhat@mirantis.com] <br><b>Sent:</b> Tuesday, November 13, 2012 11:45 AM<br><b>To:</b> OpenStack Development Mailing List<br><b>Subject:</b> Re: [openstack-dev] [Quantum][LBaaS] Architecture: Agents, Drivers, async calls<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>Some reasons why LBaaS core should be responsible for processing requests asynchronously: <o:p></o:p></p></div><ul type=disc><li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l3 level1 lfo1'>Driver code will be as simple as possible, in most cases it will just translate LBaaS model into device-specific;<o:p></o:p></li><li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l3 level1 lfo1'>There will be no dependencies between drivers and user requests will take approximately the same time for different drivers. This will avoid a case when some driver take too much time to apply config synchronously and block other requests.<o:p></o:p></li><li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l3 level1 lfo1'>REST API is already asynchronous. <o:p></o:p></li></ul><div><p class=MsoNormal>To summarize what Eugene proposed, LBaaS will consist of (see diagram <a href="http://wiki.openstack.org/Quantum/LBaaS/Architecture?action=AttachFile&do=view&target=lbaas_architecture_new.png" target="_blank">http://wiki.openstack.org/Quantum/LBaaS/Architecture?action=AttachFile&do=view&target=lbaas_architecture_new.png</a>): <o:p></o:p></p></div><ul type=disc><li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l2 level1 lfo2'>Extension - it's a front-end of a service<o:p></o:p></li><li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l2 level1 lfo2'>Plugin - responsible for request processing, persistence and core functionality (scheduling). All operations may be thought as atomic and quick. They are done synchronously.<o:p></o:p></li><li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l2 level1 lfo2'>Agent - responsible for executing commands on specific devices with help of drivers. It gets requests from Plugin via MQ and process them in asynchronous way<o:p></o:p></li><li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l2 level1 lfo2'>Driver - translates from unified API to vendor-specific. Its work may be time-consuming.<o:p></o:p></li></ul><div><div><p class=MsoNormal>Among all operations, update look the most complicated; the case of 2 concurrent updates and workflow is shown on <a href="http://wiki.openstack.org/Quantum/LBaaS/Architecture/ConcurrentRequests">http://wiki.openstack.org/Quantum/LBaaS/Architecture/ConcurrentRequests</a>. <o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Thanks,<o:p></o:p></p></div><div><p class=MsoNormal>Ilya<o:p></o:p></p></div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>2012/11/13 Youcef Laribi <<a href="mailto:Youcef.Laribi@eu.citrix.com" target="_blank">Youcef.Laribi@eu.citrix.com</a>><o:p></o:p></p><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Eugene,</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Another way to look at the workflow is to make sure that the LBaaS Plugin updates the database synchronously (and generates the resource ID before returning to the user), and then let it to the driver implementations to decide whether they want to handle the call synchronously or asynchronously.</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>I like drawing pictures to avoid misunderstandings, so here are 2 pictures illustrating 2 vendors, one deciding to implement their driver in a synchronous way, and the other one in an asynchronous way. </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Synchronous driver implementation: </span><a href="http://wiki.openstack.org/Quantum/LBaaS?action=AttachFile&do=view&target=LBaaS+synchronous+driver+implementation.png" target="_blank">http://wiki.openstack.org/Quantum/LBaaS?action=AttachFile&do=view&target=LBaaS+synchronous+driver+implementation.png</a><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Asynchronous driver implementation: </span><a href="http://wiki.openstack.org/Quantum/LBaaS?action=AttachFile&do=view&target=LBaaS+asynchronous+driver+implementation.png" target="_blank">http://wiki.openstack.org/Quantum/LBaaS?action=AttachFile&do=view&target=LBaaS+asynchronous+driver+implementation.png</a><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>As far as the plugin is concerned, the calls to drivers are always synchronous in the sense that the driver doesn’t have to deal with queues, etc. The plugin should expect the driver to return either a “COMPLETED” status (meaning the call has been executed on the device), ora “PENDING” status (meaning that the driver has started the operation but it is not complete). The plugin updates the database in both cases with the outcome of the call, and returns the result to the user. </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>This would allow a lot of freedom in driver implementations. A vendor can start with a synchronous implementation because it is quick to implement, and then later on move on to an asynchronous implementation without impacting the LBaaS plugin. Or it can implement some calls synchronously while other calls (which might take a long time to complete) asynchronously. You can also have different vendors using different driver strategies wrt. Synchronicity, or using different queuing mechanisms.</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Thanks</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Youcef</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><a name="13afa61ba5fb651b_13afa501394d9ae2_13af63"><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> </span></a><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><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"'> Eugene Nikanorov [mailto:<a href="mailto:enikanorov@mirantis.com" target="_blank">enikanorov@mirantis.com</a>] <br><b>Sent:</b> Monday, November 12, 2012 6:24 AM<br><b>To:</b> <a href="mailto:openstack-dev@lists.openstack.org" target="_blank">openstack-dev@lists.openstack.org</a><br><b>Subject:</b> [openstack-dev] [Quantum][LBaaS] Architecture: Agents, Drivers, async calls</span><o:p></o:p></p><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Hi folks,<o:p></o:p></p><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>In the latest meeting we've mentioned several important architectural points including:<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>- agents vs direct driver call<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>- asynchronous execution<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>- dispatching a generic REST call to a proper driver.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>I would like to present how Mirantis team sees this based on our previous experience with LBaaS and other openstack components.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>We need asynchronous execution in the sense that client gets immediate response while actual device configuration happens later.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Workflow of such operation could look like following:<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>1) client makes REST call; receives an object it has created/modified with PENDING status <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>2) call is dispatched to a plugin, plugin creates/modifies/etc an object in the database<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>3) plugin calls driver to apply new configuration to specific device<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>4) driver finishes applying configuration, plugin updates DB object<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>5) client polls objectID and gets final status of operation.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Now depending on approach we take, (3) could expand into different sequence of operations.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>One of the good options to choose could be using agent between plugin and drivers. In this case (3) expands to:<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>3.1 plugin posts message to mq<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>3.2. message is consumed by one of the running service agents<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>3.3. agent calls corresponding driver directly in synchronous way.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>3.4. agent posts message upon completion.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>3.5. plugin consumes the message and updates DB object with final status<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Such approach solves at least two potential problems:<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>1. plugin may be simplified since it is not required to implement call/work item queuing <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>2. Applying device configuration is time consuming task which could take seconds. <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Both plugin and agent has thread limit for any concurrent operations. <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Handling heavy workload in large deployments will be simple with several agents consuming messages from mq.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Also this allows to create synchronous drivers since asyncness will be handled by mq + agent.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Another option could be calling drivers directly without any asyncness at all while preserving above workflow (1-5). <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>That could work as temporary fast solution while allowing to split it to "plugin + agent approach" relatively easily.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Regarding the dispatching REST calls to proper driver:<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>In fact, VIP object should contain reference to particular device it is created at. <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><a href="http://wiki.openstack.org/LBaaS/CoreResourceModel/proposal" target="_blank">http://wiki.openstack.org/LBaaS/CoreResourceModel/proposal</a> misses that device management part, I think it was just implied there.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Every balancer-related object references the VIP and hence references the specific device where it was created. <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>E,g, when a call for any object is made, plugin needs to extract device type from DB following those references and later plugin or agent will use it to call particular driver.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Thanks,<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Eugene.<o:p></o:p></p></div></div></div></div></div><p class=MsoNormal style='margin-bottom:12.0pt'><br>_______________________________________________<br>OpenStack-dev mailing list<br><a href="mailto:OpenStack-dev@lists.openstack.org" target="_blank">OpenStack-dev@lists.openstack.org</a><br><a href="http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev" target="_blank">http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev</a><o:p></o:p></p></div><p class=MsoNormal><o:p> </o:p></p></div></div></body></html>