We use istio to use distributed tracing. Our microservices sometimes need to hit external APIs, which usually communicate over https.

To measure the exact performance of the whole system, we want to trace the communication when hitting an external API.  

However, distributed tracing requires access to the header of the request, but https does not allow access because the header is encrypted.  

For confirmation, I deployed bookinfo on GKE with istio enabled, entered the productpage container of the productpage pod, and executed the following command.

```
$ curl http://google.com
$ curl https://google.com

```

Only http communication was displayed on zipkin.

Is it possible to get a series of traces, including APIs that use external https?