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<p class="MsoNormal"><span style="color:#1F497D">In my opinion, it does not matter how long the full sync takes. Processing any RPC messages, even ones that are not stale, before the initial full sync completes is not guaranteed to provide consistent results.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">For example, if a port-update-end arrives before that port is received as part of the initial sync it will unnecessarily result in a full resync on that port’s network. Similarly, if a port-delete-end arrives
before that port is received as part of the initial sync then it will be added to the “deleted_ports” list but that list is not referenced during the full sync so the information for that port will remain in the DHCP configuration for that network even though
the port no longer exists. That will cause issues later when a new port is created and uses the IP address of that deleted port.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">If the core reviewers prefer using timestamps embedded within the RPC payload then we can explore that option, but that will come with backward compatibility constraints and additional complexity. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><br>
Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Allain <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#333333">Allain Legacy</span></b><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#333333">, Software Developer, Wind River</span><span style="color:#1F497D"><br>
</span><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#333333">direct 613.270.2279 fax
</span><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#333333">613.492.7870 skype allain.legacy<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#404040">350 Terry Fox Drive, Suite 200, Ottawa, Ontario, K2K 2W5<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><br>
<br>
</span><a href="http://www.windriver.com/" title=""Innovators Start Here" "><span style="font-family:"Arial",sans-serif;color:#CC0000;text-decoration:none"><img border="0" width="160" height="92" id="_x0000_i1026" src="cid:image001.png@01D495EF.0B8C6660" alt="WIND"></span></a><span style="color:#1F497D"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b>From:</b> Qin, Kailun [mailto:kailun.qin@intel.com] <br>
<b>Sent:</b> Monday, December 17, 2018 9:29 AM<br>
<b>To:</b> Legacy, Allain; Peters, Matt<br>
<b>Cc:</b> 'starlingx-discuss@lists.starlingx.io'<br>
<b>Subject:</b> RE: Questions about patch fd6cfc upstreaming<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Hi Allain, Matt,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I followed up this RFE (<a href="https://bugs.launchpad.net/neutron/+bug/1795212">https://bugs.launchpad.net/neutron/+bug/1795212</a>) and received one feedback from a Neutron core reviewer. He thinks that the
delay isn't good approach because how much time agent will need to do full sync after restart is unknown. He prefers something based on timestamps and discard messages which came before agent was started.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I believe you’ve also considered the timestamp/sequence/lifetime number based approach so that stale messages can be discarded w/ more certainty. What’s your opinion? Should we keep w/ the delay approach of DHCP
agent and discuss further in the driver meeting to see more feedbacks, in the spirit of avoiding compatibility changes and changes that would impact running against an unmodified server? Or we change our investigation direction to the timestamp-based solution?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Thanks!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">BR,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Kailun<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"></a><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><a name="_____replyseparator"></a><b>From:</b> Qin, Kailun <br>
<b>Sent:</b> Wednesday, November 21, 2018 11:01 AM<br>
<b>To:</b> Legacy, Allain <<a href="mailto:Allain.Legacy@windriver.com">Allain.Legacy@windriver.com</a>>; Peters, Matt <<a href="mailto:Matt.Peters@windriver.com">Matt.Peters@windriver.com</a>><br>
<b>Cc:</b> <a href="mailto:starlingx-discuss@lists.starlingx.io">starlingx-discuss@lists.starlingx.io</a><br>
<b>Subject:</b> RE: Questions about patch fd6cfc upstreaming<o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Allain,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Great thanks for the information! The scenario is reasonable and detailed enough for me. Let’s feedback this along with some other follow-up answers to the Neutron team and see how it goes.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">BR,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Kailun<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b>From:</b> Legacy, Allain [<a href="mailto:Allain.Legacy@windriver.com">mailto:Allain.Legacy@windriver.com</a>]
<br>
<b>Sent:</b> Wednesday, November 21, 2018 2:13 AM<br>
<b>To:</b> Qin, Kailun <<a href="mailto:kailun.qin@intel.com">kailun.qin@intel.com</a>>; Peters, Matt <<a href="mailto:Matt.Peters@windriver.com">Matt.Peters@windriver.com</a>><br>
<b>Cc:</b> <a href="mailto:starlingx-discuss@lists.starlingx.io">starlingx-discuss@lists.starlingx.io</a><br>
<b>Subject:</b> RE: Questions about patch fd6cfc upstreaming<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">We only observed this type of issue in a large office configuration where the neutron-server is overloaded during a DOR test (dead office recovery) where all nodes are powered off and back on. In such a scenario
the system is overloaded for an extended period and there is a long delay between when events occur and when notifications are received by subscribers. It is difficult to reproduce this on small systems where the time between event and notification is short.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I don’t remember the exact details of the entire scenario, but the high level issue was that we wanted to avoid agents receiving and processing RPC messages that were sent to them before they started up. That
happens more frequently in a DOR test because the server has a stale view of the system state and can send RPC messages to nodes that are not enabled yet. That is, its agent DB table may show that all agents are healthy depending on how long it took for
the DOR to recover the controller node. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">What we found was that it was possible for the server to think that the agent was up when it was actually down. During the window where the server sees the agent as up it can send it RPC messages. Those messages
get queued up and delivered to the agent once it is finally up. The problem is since the agent was not actually up in the first place those messages were never really valid. Therefore we wanted the agent to discard any RPC requests until after it was able
to resync to the server. This allowed the system to avoid unnecessary transitions based on old data.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">One of the specific problems that this was addressing was something like this:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="color:#1F497D">A subnet had no remaining IP addresses to allocated<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="color:#1F497D">A DCHP agent (agent-X) received a stale message to “create network” so it reserved a DHCP port with an IP address (this used the last available IP address)<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore">3.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="color:#1F497D">Meanwhile, the DHCP agent (agent-Y) that actually was assigned the network came up and was not able to reserve a DHCP port because there were no IP addresses available<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore">4.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="color:#1F497D">The first agent (agent-X) was taken down because its node was rebooted by system maintenance<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore">5.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="color:#1F497D">The second agent (agent-Y) never retries the DHCP port creation because the DHCP agent has no periodic audit so there was no DHCP server servicing the network<o:p></o:p></span></p>
<p class="MsoListParagraph"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoListParagraph"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Allain<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<div>
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#333333">Allain Legacy</span></b><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#333333">, Software Developer, Wind River</span><span style="color:#1F497D"><br>
</span><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#333333">direct 613.270.2279 fax 613.492.7870 skype allain.legacy<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif;color:#404040">350 Terry Fox Drive, Suite 200, Ottawa, Ontario, K2K 2W5<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><br>
<br>
</span><a href="http://www.windriver.com/" title=""Innovators Start Here" "><span style="font-family:"Arial",sans-serif;color:#CC0000;text-decoration:none"><img border="0" width="160" height="92" id="Picture_x0020_1" src="cid:image001.png@01D495EF.0B8C6660" alt="WIND"></span></a><span style="color:#1F497D"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b>From:</b> Qin, Kailun [<a href="mailto:kailun.qin@intel.com">mailto:kailun.qin@intel.com</a>]
<br>
<b>Sent:</b> Tuesday, November 20, 2018 2:02 AM<br>
<b>To:</b> Peters, Matt<br>
<b>Cc:</b> <a href="mailto:starlingx-discuss@lists.starlingx.io">starlingx-discuss@lists.starlingx.io</a><br>
<b>Subject:</b> [Starlingx-discuss] Questions about patch fd6cfc upstreaming<o:p></o:p></p>
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</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hi Matt,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m working on the patch fd6cfc upstreaming, which tries to address the stale RPC message issue when DHCP agent restarting up.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The patch was in good shape <a href="https://review.openstack.org/609463/">
https://review.openstack.org/609463/</a> whereas the neutron community was questioning about the exact failure modes of this issue. The DHCP agent will have a full sync after the agent restarting up (<a href="https://github.com/openstack/neutron/blob/master/neutron/agent/dhcp/agent.py#L195">https://github.com/openstack/neutron/blob/master/neutron/agent/dhcp/agent.py#L195</a>),
what kind of corner cases and negative behaviors could happen even w/ this full sync?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Based on the commit message, I tried to reproduce this issue w/ the following steps:<o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:.25in;text-indent:-.25in;mso-list:l0 level1 lfo4">
<![if !supportLists]><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>schedule network1 to agent1.<o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:.25in;text-indent:-.25in;mso-list:l0 level1 lfo4">
<![if !supportLists]><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>turn down agent1 at almost the same time.<o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:.25in;text-indent:-.25in;mso-list:l0 level1 lfo4">
<![if !supportLists]><span style="mso-list:Ignore">3.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>network1 is rescheduled to agent2 after finding that agent1 is dead.<o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:.25in;text-indent:-.25in;mso-list:l0 level1 lfo4">
<![if !supportLists]><span style="mso-list:Ignore">4.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>turn up agent1, expecting stale RPC messages to be received by agent1 so that both agent1 and agent2 are servicing network1.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">However, I can only meet the described failure mode by sending another scheduling operation (network1->agent1) after step 2) is done. For the others, they seem to work as expected.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Would you please kindly help provide more details about the failure pattern of this issue and/or the reproduction steps? Thanks a lot.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">BR,<o:p></o:p></p>
<p class="MsoNormal">Kailun<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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