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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">Hi Yujun,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">You started an interesting discussion. I think that the distinction between an operational error and a programmer error is correct and we should always keep that in mind.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">I agree that having an overall design for error handling in Vitrage is a good idea; but I disagree that until then we better let it crash.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">I think that Vitrage is made out of many pieces that don’t necessarily depend on one another. For example, if one datasource fails, everything else can work as usual – so why crash? Similarly,
if one template fails to load, all other templates can still be activated. <o:p>
</o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">Another aspect is that the main purpose of Vitrage is to provide insights. In case of a failure in one datasource/template, some of the insights might be missing. But this will not lead
to inaccurate behavior or to wrong actions being executed in the system. IMO, we should give the user as much information as possible given that we have only part of the input.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">Regarding the use cases that you mentioned:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<ol style="margin-top:0cm" start="1" type="1">
<li class="MsoNormal" style="mso-list:l0 level1 lfo1"><span style="font-size:11.0pt;font-family:Calibri">invalid configuration file<o:p></o:p></span></li></ol>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt;font-family:Calibri">[Ifat] This should depend on the specific configuration. If keystone is misconfigured, nothing will work of course. But if for example Zabbix is misconfigured,
Vitrage should work and show the topology and the non-Zabbix alarms. <o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<ol style="margin-top:0cm" start="2" type="1">
<li class="MsoNormal" style="mso-list:l0 level1 lfo1"><span style="font-size:11.0pt;font-family:Calibri">failed to communicate with data source<o:p></o:p></span></li></ol>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt;font-family:Calibri">[Ifat] I think that the error should be logged, and all other datasources should work as usual.
<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<ol style="margin-top:0cm" start="3" type="1">
<li class="MsoNormal" style="mso-list:l0 level1 lfo1"><span style="font-size:11.0pt;font-family:Calibri">malformed data from data source<o:p></o:p></span></li></ol>
<p class="MsoListParagraph"><span style="font-size:11.0pt;font-family:Calibri">[Ifat] I think that the error should be logged, and all other datasources should work as usual. This problem means we must modify the code in the datasource itself, but until then
Vitrage should work, right?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<ol style="margin-top:0cm" start="4" type="1">
<li class="MsoNormal" style="mso-list:l0 level1 lfo1"><span style="font-size:11.0pt;font-family:Calibri">failed to execute an action<o:p></o:p></span></li></ol>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt;font-family:Calibri">[Ifat] Again, that’s a problem that requires code changes; but why fail other actions?<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<ol style="margin-top:0cm" start="5" type="1">
<li class="MsoNormal" style="mso-list:l0 level1 lfo1"><span style="font-size:11.0pt;font-family:Calibri">...<o:p></o:p></span></li></ol>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">BTW, it might be a good idea to add API/UI for showing the configuration and the status of the datasources. We all know that errors in the log files are often ignored…<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">Best Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">Ifat.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span style="font-family:Calibri;color:black">From: </span>
</b><span style="font-family:Calibri;color:black">"Yujun Zhang (ZTE)" <zhangyujun+zte@gmail.com><br>
<b>Reply-To: </b>"OpenStack Development Mailing List (not for usage questions)" <openstack-dev@lists.openstack.org><br>
<b>Date: </b>Monday, 29 May 2017 at 16:13<br>
<b>To: </b>"OpenStack Development Mailing List (not for usage questions)" <openstack-dev@lists.openstack.org><br>
<b>Subject: </b>[openstack-dev] [vitrage] error handling<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">Brought up by a recent code review, I think it worth a thorough discussion about the error handling rule.
<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I once read an article[1] from Joyent and it impressed me on the distinguish between
<b>Operational</b> errors vs. <b>programmer</b> errors. The article is written for nodejs, but the principle also applies for other programming language.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The basic rule recommended by Joyent is <o:p></o:p></p>
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<h3 style="mso-margin-top-alt:16.5pt;margin-right:0cm;margin-bottom:8.25pt;margin-left:0cm;box-sizing:border-box">
<span style="font-size:21.0pt;font-family:Helvetica;color:#333333;font-weight:normal">Handling operational errors<o:p></o:p></span></h3>
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<h3 style="mso-margin-top-alt:16.5pt;margin-right:0cm;margin-bottom:8.25pt;margin-left:0cm;box-sizing:border-box">
<span style="font-size:21.0pt;font-family:Helvetica;color:#333333;font-weight:normal">(Not) handling programmer errors<o:p></o:p></span></h3>
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<p class="MsoNormal">There is also one rule in openstack style guide line[2] close to this idea.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Arial;color:#3E4349">[H201] Do not write<span class="inbox-inbox-apple-converted-space"> </span></span><span class="inbox-inbox-pre"><span style="font-size:10.0pt;font-family:"Courier New";color:#3E4349">except:</span></span><span style="font-size:11.0pt;font-family:Arial;color:#3E4349">,
use<span class="inbox-inbox-apple-converted-space"> </span></span><span class="inbox-inbox-pre"><span style="font-size:10.0pt;font-family:"Courier New";color:#3E4349">except</span></span><span class="inbox-inbox-apple-converted-space"><span style="font-size:10.0pt;font-family:"Courier New";color:#3E4349"> </span></span><span class="inbox-inbox-pre"><span style="font-size:10.0pt;font-family:"Courier New";color:#3E4349">Exception:</span></span><span class="inbox-inbox-apple-converted-space"><span style="font-size:11.0pt;font-family:Arial;color:#3E4349"> </span></span><span style="font-size:11.0pt;font-family:Arial;color:#3E4349">at
the very least. When catching an exception you should be as specific so you don’t mistakenly catch unexpected exceptions.</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I do think before we have a well designed error handling, it is better to let it crash. It is dangerous to hide the errors and keep the system running in undetermined states.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">So the question is <b>what kind of operational errors are we facing in vitrage?</b> I can think of something like<o:p></o:p></p>
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<ol start="1" type="1">
<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo2">
invalid configuration file<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo2">
failed to communicate with data source<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo2">
malformed data from data source<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo2">
failed to execute an action<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo2">
...<o:p></o:p></li></ol>
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<p class="MsoNormal">Maybe this could be the first step for the error handling design.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">[1]: <a href="https://www.joyent.com/node-js/production/design/errors">https://www.joyent.com/node-js/production/design/errors</a><o:p></o:p></p>
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<p class="MsoNormal">[2]: <a href="https://docs.openstack.org/developer/hacking/">https://docs.openstack.org/developer/hacking/</a><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">-- <o:p></o:p></p>
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<p class="MsoNormal">Yujun Zhang<o:p></o:p></p>
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