KIALI-1313 Fix Apps not being resoved correctly for a service

[israel-hdez]

Apps were being resolved using k8s-deployments. This is incorrect since
a service can cover several kinds of "deployments".

This issue was found because metrics were being fetched incorrectly for
services that are backed by something else than a k8s-deployment.

Using pods to resolve apps involved in a k8s-service.

[israel-hdez]

@jshaughn @jotak Probably I'm not understanding correctly the code, but what I can see is that the "metrics" tab of the "service details" page is not showing metrics for services, but - instead - it's showing metrics for "apps". For the bookinfo sample, the resulting metrics happen to be the same.

The Prometheus queries that are being built are like the following:

round(sum(rate(istio_tcp_received_bytes_total{reporter="destination",destination_app=~"frontend",destination_workload_namespace="pets"}[72s])), 0.001)

So, destination_app is the label being requested. Not sure if this is really correct or if I'm missing something in the code, or perhaps this is the intention.

I'm just commenting if, by chance, that's incorrect.

[jotak]

@israel-hdez good catch! Thanks.

About using app versus service metrics: at the moment, it's done on purpose, because we don't have yet our WorkloadDetails view so we would miss to many metrics if we were strictly focusing on service metrics. In that sense, we're pretty much having the same behaviour than before our istio-1 epic.

But that may change quickly in the future. I have to talk with @lucasponce about that!

[jotak]

LGTM