10:09 a.m.
I want to make sure I understand the difference between trace and span. A trace captures
the call between two services whether those are REST endpoints, EJBs, etc. Let’s say we
want a trace of A calling B. Within that A calls C which in turn calls D, etc. and then
finally B is called. Would a span measure the duration of the call between C and D?
Are all spans captured/recorded by default?
Would this be optional functionality? I am wondering because it obviously requires having
Hawkular Metrics running which also means Cassandra.
Under what tenant would you store these metrics?
On Jan 7, 2017, at 7:36 AM, Gary Brown <gbrown(a)redhat.com>
wrote:
Hi
Wanted to discuss a proposal for recording some metric data captured from Hawkular APM in
Hawkular Metrics.
For those not familiar with Hawkular APM, it captures the end to end trace instance
(think of it as a distributed call stack), for each invocation of an application. This
trace can include information about the communications between services, but can also
include details about internal components used within the services (e.g. EJBs, database
calls, etc).
First point is that if we were to record duration metrics for each 'span'
captured (i.e. scope within which a task is performed), for each invocation of an
application, then it would result in a large amount of data that may be of no interest. So
we need to find a way for end users/developers to express which key points within an
application they do want recorded as metrics.
The proposal is to allow the application/services to define a tag/property on the spans
of interest, e.g. 'kpi', that would indicate to the server that the duration value
for the span should be stored in H-Metrics. The value for the tag should define the
name/description of the KPI.
If considered a suitable solution, then we can also propose it as a standard tag in the
OpenTracing standard.
There are a couple of metrics that we could record by default, first being the trace
instance completion time, and the second possibly being the individual service response
times (although this could potentially also be governed by the 'kpi' tag).
Thoughts?
Regards
Gary
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