Istio Distributed Tracing shows just 1 span

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 ;-)

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