tornado_opentracing 0.1.0

OpenTracing support for Tornado applications

This package enables distributed tracing in Tornado projects via The OpenTracing Project. Once a production system contends with real concurrency or splits into many services, crucial (and formerly easy) tasks become difficult: user-facing latency optimization, root-cause analysis of backend errors, communication about distinct pieces of a now-distributed system, etc. Distributed tracing follows a request on its journey from inception to completion from mobile/browser all the way to the microservices.

As core services and libraries adopt OpenTracing, the application builder is no longer burdened with the task of adding basic tracing instrumentation to their own code. In this way, developers can build their applications with the tools they prefer and benefit from built-in tracing instrumentation. OpenTracing implementations exist for major distributed tracing systems and can be bound or swapped with a one-line configuration change.

If you want to learn more about the underlying python API, visit the python source code.

Installation

Run the following command:

$ pip install tornado_opentracing

Setting up Tracing for All Requests

In order to implement tracing in your system (for all the requests), add the following lines of code to your site’s Application constructor to enable tracing:

import tornado_opentracing

# Initialize tracing before creating the Application object
tornado_opentracing.init_tracing()

# OpenTracing settings
app = Application(
    ''' Other parameters here '''
    opentracing_tracer=tornado_opentracing.TornadoTracer(some_opentracing_tracer),
    opentracing_trace_all=True, # defaults to False
    opentracing_trace_client=True, # AsyncHTTPClient tracing, defaults to False
    opentracing_traced_attributes=['method'], # only valid if `trace all` == True
    opentracing_start_span_cb=my_start_span_cb,
)

Note: Valid request attributes to trace are listed [here](http://www.tornadoweb.org/en/stable/httputil.html#tornado.httputil.HTTPServerRequest). When you trace an attribute, this means that created spans will have tags with the attribute name and the request’s value.

Tracing All Requests

In order to trace all requests, set opentracing_trace_all=True when creating Application. If you want to trace any attributes for all requests, then add them to opentracing_traced_attributes. For example, if you wanted to trace the uri and method, then set opentracing_traced_attributes = [‘uri’, ‘method’].

opentracing_start_span_cb is a callback invoked after a new Span has been created, and it must have two parameters: the new Span and the request object.

By default, no tracing happens for AsyncHTTPClient, but this can be enabled by setting opentracing_trace_client=True.

Tracing requires tracing to be set up before Application is created through the init_tracing method, which will patch the RequestHandler, Application and other Tornado components.

tornado_opentracing.init_tracing()

Tracing Individual Requests

If you don’t want to trace all requests to your site, then you can use function decorators to trace individual functions. This can be done by managing a globally unique TornadoTracer object yourself, and adding the following lines of code to any get/post/put/delete function of your RequestHandler sub-classes:

tracer = TornadoTracer(some_opentracing_tracer)

class MyRequestHandler(tornado.web.RequestHandler):
    # put the decorator before @tornado.gen.coroutine, if used
    @tracer.trace(['uri', 'method']) # optionally pass a list of traced attributes
    def get(self):
        ... # do some stuff

This tracing method doesn’t use the Application settings, and there is not need to call init_tracing.

The optional arguments allow for tracing of request attributes.

Tracing Client Requests only

For applications using only the http client (no tornado.web usage), client tracing can be enabled like this:

tornado_opentracing.init_client_tracing(tracer)

init_client_tracing takes an OpenTracing-compatible tracer, and can optionally take a start_span_cb parameter as callback. This call is not required when required when using trace_all with the init_tracing initialization, but is required when the user handles the tracer and uses the tracer.trace() decoration.

Examples

Here is a simple example of a Tornado application that log all requests:

Other examples are included under the examples directrory.

Further Information

If you’re interested in learning more about the OpenTracing standard, please visit opentracing.io or join the mailing list. If you would like to implement OpenTracing in your project and need help, feel free to send us a note at [e-mail].