Example

This example has a flask client and server and shows how to trace the requests to a webserver from a client using the flask_opentracing extension and a concrete variant of an OpenTracing tracer. To run, make sure that you run pip install for flask, opentracing, jaeger_client.

Set up Jaeger:

First, we'll have to download and run our Jaeger instance. It collects and displays traces in neat graphical format.

If you already have Docker installed, run this:

docker run -d -e \
  COLLECTOR_ZIPKIN_HTTP_PORT=9411 \
  -p 5775:5775/udp \
  -p 6831:6831/udp \
  -p 6832:6832/udp \
  -p 5778:5778 \
  -p 16686:16686 \
  -p 14268:14268 \
  -p 9411:9411 \
  jaegertracing/all-in-one:latest

You should be able to see a web interface by browsing to http://localhost:16686/search

Now, open two terminals and navigate to this directory. Run the following commands in each terminal:

First window:

> python3 server.py   

Give it few seconds to start and run this in second window:

> python3 client.py   

To see the traced requests, go to Jaeger web interface and refresh the page. Select your service name from dropdown on the left (it's "jaeger_opentracing_example" in our case) and press Find traces button at the bottom of the page.

(NOTE: if you wish to use a different OpenTracing tracer instead of Jaeger, simply replace jaeger_tracer with the OpenTracing tracer instance of your choice.)

Trace a request from browser:

Browse to http://localhost:5000/log and compare the trace in Jaeger. The last one has 2 spans instead of 3. The span of webserver's GET method is missing. That is because client.py starts a trace and passes trace context over the wire, whereas the request from your browser has no tracing context in it.

Add spans to the trace manually:

In log function of the server app, we are creating current_span. This is done to trace the work that is being done to render the response to /log endpoint. Suppose there's a database connection happening. By creating a separate span for it, you'll be able to trace the DB request separately from rendering or the response. This gives a lot of flexibility to the user.

Speaking about databases, using install_all_patches() method from opentracing_instrumentation package gives you a way to trace your MySQLdb, SQLAlchemy, Redis queries without writing boilerplate code.

Following code shows how to create a span based on already existing one.

# child_scope.span automatically inherits from the Span created
# for this request by the Flask instrumentation.
child_scope = jaeger_tracer.start_active_span('inside create_child_span')
... do some stuff
child_scope.close()