Istio Distributed Tracing shows just 1 span - kubernetes

Question

I'm following this guide, with Zipkin.
I have 3 microservices involed, A -> B -> C, I'm propagating headers from A to B and from B to C.
But in the Zipkin dashboard I only see entries for A -> B and B -> C, not A -> B -> C.
Those are the headers:
[
"x-request-id",
"x-b3-traceid",
"x-b3-spanid",
"x-b3-parentspanid",
"x-b3-sampled",
"x-b3-flags",
"x-ot-span-context"
]
I can see that in B x-b3-parentspanid is null and I guess that's wrong, but the other are working I think...how is it possible?
EDIT:
added code snippets to show headers propagation
A -> B propagation:
app.post("/job", (req, res) => postJob(req.body, req.headers).then((response) => res.send(response)))
...
const postJob = (job, headers) => rp({
method: "POST",
uri: `${API_ENDPOINT}/api/job`,
json: true,
body: job,
headers: Object.keys(headers).filter((key) => TRACING_HEADERS.includes(key)).map((key) => headers[key])
})
B -> C propagation:
#PostMapping("/api/job")
#ResponseBody
fun publish(
#RequestBody job: Job,
#RequestHeader("x-request-id") xreq: String?,
#RequestHeader("x-b3-traceid") xtraceid: String?,
#RequestHeader("x-b3-spanid") xspanid: String?,
#RequestHeader("x-b3-parentspanid") xparentspanid: String?,
#RequestHeader("x-b3-sampled") xsampled: String?,
#RequestHeader("x-b3-flags") xflags: String?,
#RequestHeader("x-ot-span-context") xotspan: String?
): JobResponse = jobsService.publishJob(
job, mapOf(
"x-request-id" to xreq,
"x-b3-traceid" to xtraceid,
"x-b3-spanid" to xspanid,
"x-b3-parentspanid" to xparentspanid,
"x-b3-sampled" to xsampled,
"x-b3-flags" to xflags,
"x-ot-span-context" to xotspan
)
)
...
fun publishJob(job: Job, headers: Map<String, String?>): JobResponse {
val enabled = restTemplate.exchange(
"${gatekeeperConfiguration.endpoint}/",
HttpMethod.GET,
HttpEntity(headers),
EnabledResponse::class.java
).body
if (!enabled!!.isEnabled) // TODO we intentionally want this to crash if body is null
return JobResponse(JobRequestStatus.REJECTED)
return if (this.queue.publish(job)) JobResponse(JobRequestStatus.OK)
else throw RuntimeException("I don't know what to do, yet")
}

Answer 1

Object.keys(headers).filter((key) => TRACING_HEADERS.includes(key)).map((key) => headers[key]) returns an array.
What you want is:
Object.keys(headers)
.filter(key => TRACING_HEADERS.includes(key))
.reduce((obj, key) => {
obj[key] = headers[key];
return obj;
}, {})
I'm pretty sure this isn't an istio / distributed tracing issue ;-)

Answer 2

b3-propagation of x-b3-parentspanid (https://github.com/openzipkin/b3-propagation) can be configured in your application.yml by adding:
opentracing:
jaeger:
enable-b3-propagation: true