[osprofiler] Distributed tracing in OpenStack
skaplons at redhat.com
Fri Apr 12 15:46:05 UTC 2019
> Wiadomość napisana przez Monty Taylor <mordred at inaugust.com> w dniu 12.04.2019, o godz. 16:34:
> On 4/11/19 9:42 PM, Ilya Shakhat wrote:
>> Distributed tracing is one of must-have features when one wants to track the full path of request going through different services and APIs. This makes it similar to shared request-id, but with nice visualization at the end . In OpenStack the tracing can be achieved via osprofiler library. The library was introduced 5 years ago, and back then there was no standard approach on how to do tracing and that's why it stays aside from what has become a mainstream. Yet there is no single standard, but the major players are OpenTracing and OpenCensus communities. OpenTracing is represented by Uber's Jaeger which is the default tracer from k8s world.
>> Issues and limitations to be fixed:
>> 1. Compatibility. While osprofiler library supports many different storage drivers, it has only one way of transferring trace context over the wire. Ideally the library should be compatible with other third-party tracers and allow traces to start in front of OpenStack APIs (e.g. in user apps) and continue after (e.g. in storage systems, or network management tools). 
>> 2. Operation mode. With osprofiler tracing is initiated by user request, while in industrial solutions the tracing can be managed centrally via dynamic sampling policies.
>> 3. In-process trace propagation. Depending on execution model (threaded, async) the ways of storing current trace context differ. OSProfiler supports thread-local model, which recently got broken with new async implementation in openstacksdk .
> FWIW - we should have re-fixed that issue in SDK for all instances other than parallel uploading of Large Objects segments to swift. The parallism support now relies on the calling context's parallism. The large-object segment uploader is a thing we should make sure we do things with to make sure we're not losing those interactions.
> That said - if we move forward with this plan - let's be sure to make sure it works in openstacksdk - and that we're testing it so that we don't break it.
There is even storyboard for that issue https://storyboard.openstack.org/#!/story/2004618
>> With OpenTracing it is possible to select the appropriate model alongside with tracer configuration.
>> What's the plan:
>> Switching to OpenTracing could be a good option to gain compatibility with 3rd-party solutions. The actual change should go to osprofiler library, but indirectly affects all OpenStack projects (should it be a global team goal then?). I'm going to make a PoC of proposed change, so reviews would be highly appreciated.
>> Comments, suggestions?
> Generally supportive. I have specific impl feedbacks - but I'll leave those on the patches.
>>  e.g. http://logs.openstack.org/15/650915/4/check/tempest-smoke-py3-osprofiler-redis/7c6c14e/osprofiler-traces/trace-3e5cc660-8815-4079-86b9-778af8469d79.html.gz
>>  https://bugs.launchpad.net/osprofiler/+bug/1798565
>>  https://bugs.launchpad.net/osprofiler/+bug/1818493
Senior software engineer
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