Expose Jaeger agent port as environment variable on deployment manifest

[masroorhasan]

The default configuration for Jaeger tracing allows specifying jaeger agent host address but hardcodes port 5775 (for zipkin.thrift over thrift protocol).

jaeger_serv = os.environ.get("JAEGER_AGENT_HOST","0.0.0.0")
        jaeger_config = os.environ.get("JAEGER_CONFIG_PATH",None)
        if jaeger_config is None:
            logger.info("Using default tracing config")
            config = Config(
                config={ # usually read from some yaml config
                    'sampler': {
                        'type': 'const',
                        'param': 1,
                    },
                    'local_agent': {
                        'reporting_host': jaeger_serv,
                        'reporting_port': 5775,
                    },
                    'logging': True,
                },
                service_name=args.interface_name,
                validate=True,
            )

However, Jaeger agent exposes multiple UDP ports to support jaeger.thrift and binary thrift as well: https://www.jaegertracing.io/docs/1.8/deployment/#agent

The default seldon python deployment should expose enabling the agent port through environment variable so users can pick the right port to configure clients (for example, 6831).

Setting that with configuration YAML mounted on config map does not cover all use cases of setting host and port. For example, Jaeger agent works best deployed as a Daemonset on each Node, with deployments scheduled on Node only needs to send data to its local agent. Setting status.hostIP on the data in a config map is not supported native (could mount and sed update the value but that seems like a hack).

Basically, proposing to support this on a seldon deployment:

         - name: JAEGER_AGENT_HOST
            valueFrom:
              fieldRef:
                fieldPath: status.hostIP
          - name: JAEGER_AGENT_PORT
             value: "6831"

Proposed change: master...masroorhasan:masroor/jaeger-port

If the above change is ok, I'd like to submit a PR (pending discussion on the change). I assume docs and example would need to be updated as well.

Thanks!

[ukclivecox]

Your proposed change makes sense.
We should fully support Jaeger configuration.
Please do a PR.