How to understand span tag peer.address?

[gxxxh]

I have deployed Jaeger on istio to monitor the bookinfo application. Then I want to analyze the trace data of Jaeger. However, I am confused by some span tags, such as, upstream_cluster and peer address. I found the meaning of peer.address from https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/sdk_exporters/zipkin.md
, It says that peer.address means remote address. I think it means that when a client start a request and a server receive the request, the client's peer.address will be the server and the server's peer address will be the client.

Here is some information I get from one trace with 8 spans.

             spanID                                      operationName          podIP           serviceName               pid   refType   peer.address span.kind
0  0044bea01e572833  productpage.default.svc.cluster.local:9080/pro...  10.244.27.204  istio-ingressgateway                               192.168.0.49    client
1  a2bdd3593ab25d00  productpage.default.svc.cluster.local:9080/pro...  10.244.27.238   productpage.default  0044bea01e572833  CHILD_OF  10.244.27.204    server
2  626e09f9758da789           details.default.svc.cluster.local:9080/*  10.244.27.238   productpage.default  a2bdd3593ab25d00  CHILD_OF  10.244.27.238    client
3  5a76f143f0e5c301           details.default.svc.cluster.local:9080/*  10.244.27.247       details.default  626e09f9758da789  CHILD_OF  10.244.27.238    server
4  9c1aaf91ea5e5ce9           reviews.default.svc.cluster.local:9080/*  10.244.27.238   productpage.default  a2bdd3593ab25d00  CHILD_OF  10.244.27.238    client
5  923db83990a9e7e5           reviews.default.svc.cluster.local:9080/*  10.244.27.246       reviews.default  9c1aaf91ea5e5ce9  CHILD_OF  10.244.27.238    server
6  8e3dbd4dd0b70f85           ratings.default.svc.cluster.local:9080/*  10.244.27.246       reviews.default  923db83990a9e7e5  CHILD_OF  10.244.27.246    client
7  f227decb8d8b2c51           ratings.default.svc.cluster.local:9080/*  10.244.27.217       ratings.default  8e3dbd4dd0b70f85  CHILD_OF  10.244.27.246    server

However, the peer.address seems to be it's parent span's pod id, which is different from what I understand, and I don't know which is right.

Besides, I don't understand the meaning of upstream_cluster and downstream_cluster as below. Why all downstream_cluster is None, and what is the meaning of '9080' and 'inbound' in outstream_cluster?

             spanID                                      operationName          podIP  ...                                   upstream_cluster downstream_cluster span.kind
0  0044bea01e572833  productpage.default.svc.cluster.local:9080/pro...  10.244.27.204  ...  outbound|9080||productpage.default.svc.cluster...                  -    client
1  a2bdd3593ab25d00  productpage.default.svc.cluster.local:9080/pro...  10.244.27.238  ...                                     inbound|9080||                  -    server
2  626e09f9758da789           details.default.svc.cluster.local:9080/*  10.244.27.238  ...   outbound|9080||details.default.svc.cluster.local                  -    client
3  5a76f143f0e5c301           details.default.svc.cluster.local:9080/*  10.244.27.247  ...                                     inbound|9080||                  -    server
4  9c1aaf91ea5e5ce9           reviews.default.svc.cluster.local:9080/*  10.244.27.238  ...   outbound|9080||reviews.default.svc.cluster.local                  -    client
5  923db83990a9e7e5           reviews.default.svc.cluster.local:9080/*  10.244.27.246  ...                                     inbound|9080||                  -    server
6  8e3dbd4dd0b70f85           ratings.default.svc.cluster.local:9080/*  10.244.27.246  ...   outbound|9080||ratings.default.svc.cluster.local                  -    client
7  f227decb8d8b2c51           ratings.default.svc.cluster.local:9080/*  10.244.27.217  ...                                     inbound|9080||                  -    server

[yurishkuro]

I recommend asking these questions in the istio project, since it's istio that's generating these tags, Jaeger is just displaying them.