Add exception tracing examples

Update README with demo guideline.

README.md

@@ -46,6 +46,24 @@ Run Jaeger container locally to collect tracing data from Flask application
 docker run -p 16686:16686 -p 6831:6831/udp jaegertracing/all-in-one
 ```
 
-## Features
+## Demo
 
-*ToDo
+Make sure you have Flask application running and jaeger running.
+
+- Make GET requests to below APIs
+
+    ```
+    localhost:5000
+    localhost:5000/zero
+    localhost:5000/zero-unhandled
+    localhost:5000/zero-trace
+    ```
+
+- Go to jaeger home page and select service `my-helloworld-service` to find trace
+
+    ```
+    http://localhost:16686/search
+    ```
+
+- Notice the number of spans for each request. We can add more spans to each
+REST API for better detailed traces.

app.py

@@ -8,16 +8,18 @@
 from dotenv import load_dotenv
 
 from opentelemetry import trace
-from opentelemetry.exporter.jaeger.thrift import JaegerExporter
 from opentelemetry.sdk.resources import SERVICE_NAME, Resource
 from opentelemetry.sdk.trace import TracerProvider
+from opentelemetry.trace.status import StatusCode
+from opentelemetry.instrumentation.flask import FlaskInstrumentor
+from opentelemetry.instrumentation.requests import RequestsInstrumentor
+
 from opentelemetry.sdk.trace.export import (
     ConsoleSpanExporter,
     SimpleSpanProcessor,
     BatchSpanProcessor
 )
-from opentelemetry.instrumentation.flask import FlaskInstrumentor
-from opentelemetry.instrumentation.requests import RequestsInstrumentor
+from opentelemetry.exporter.jaeger.thrift import JaegerExporter
 
 load_dotenv()  # take environment variables from .env
 
@@ -37,6 +39,7 @@
 # add exporter to trace
 trace.get_tracer_provider().add_span_processor(
     BatchSpanProcessor(jaeger_exporter)
+    # SimpleSpanProcessor(ConsoleSpanExporter)
 )
 
 app = Flask(__name__)
@@ -56,7 +59,34 @@ def get(self):
             print("Hello World", data)
         return {'hello': 'world'}
 
+
+
+class ZeroDivision(REST_Resource):
+    def get(self):
+        try:
+            explode = 1/0
+        except ZeroDivisionError as error:
+            span = trace.get_current_span()
+            span.record_exception(error)
+            span.set_status(StatusCode.ERROR)
+
+
+class ZeroDivisionUnHandled(REST_Resource):
+    def get(self):
+        tracer = trace.get_tracer(__name__)
+        with tracer.start_as_current_span("ZeroDivisonUnHandled"):
+            explode = 1/0
+
+
+class ZeroDivisionZeroTrace(REST_Resource):
+    def get(self):
+        explode = 1/0
+
+
 api.add_resource(HelloWorld, '/')
+api.add_resource(ZeroDivision, '/zero')
+api.add_resource(ZeroDivisionUnHandled, '/zero-unhandled')
+api.add_resource(ZeroDivisionZeroTrace, '/zero-trace')
 
 
 if __name__ == "__main__":