opentracing 1.3.0

Required Reading

In order to understand the Python platform API, one must first be familiar with the OpenTracing project and terminology more specifically.

Status

In the current version, opentracing-python provides only the API and a basic no-op implementation that can be used by instrumentation libraries to collect and propagate distributed tracing context.

Future versions will include a reference implementation utilizing an abstract Recorder interface, as well as a Zipkin-compatible Tracer.

Usage

The work of instrumentation libraries generally consists of three steps:

1. When a service receives a new request (over HTTP or some other protocol), it uses OpenTracing’s inject/extract API to continue an active trace, creating a Span object in the process. If the request does not contain an active trace, the service starts a new trace and a new root Span.

2. The service needs to store the current Span in some request-local storage, where it can be retrieved from when a child Span must be created, e.g. in case of the service making an RPC to another service.

3. When making outbound calls to another service, the current Span must be retrieved from request-local storage, a child span must be created (e.g., by using the start_child_span() helper), and that child span must be embedded into the outbound request (e.g., using HTTP headers) via OpenTracing’s inject/extract API.

Below are the code examples for steps 1 and 3. Implementation of request-local storage needed for step 2 is specific to the service and/or frameworks / instrumentation libraries it is using (TODO: reference to other OSS projects with examples of instrumentation).

def handle_request(request):
    span = before_request(request, opentracing.tracer)
    # use span as Context Manager to ensure span.finish() will be called
    with span:
        # store span in some request-local storage
        with RequestContext(span):
            # actual business logic
            handle_request_for_real(request)


def before_request(request, tracer):
    span_context = tracer.extract(
        format=Format.HTTP_HEADERS,
        carrier=request.headers,
    )
    span = tracer.start_span(
        operation_name=request.operation,
        child_of(span_context))
    span.set_tag('http.url', request.full_url)

    remote_ip = request.remote_ip
    if remote_ip:
        span.set_tag(tags.PEER_HOST_IPV4, remote_ip)

    caller_name = request.caller_name
    if caller_name:
        span.set_tag(tags.PEER_SERVICE, caller_name)

    remote_port = request.remote_port
    if remote_port:
        span.set_tag(tags.PEER_PORT, remote_port)

    return span

Outbound request

Somewhere in your service that’s about to make an outgoing call:

from opentracing.ext import tags
from opentracing.propagation import Format
from opentracing_instrumentation import request_context

from opentracing.ext import tags
from opentracing.propagation import Format
from opentracing_instrumentation import request_context

# create and serialize a child span and use it as context manager
with before_http_request(
    request=out_request,
    current_span_extractor=request_context.get_current_span):

    # actual call
    return urllib2.urlopen(request)


def before_http_request(request, current_span_extractor):
    op = request.operation
    parent_span = current_span_extractor()
    outbound_span = opentracing.tracer.start_span(
        operation_name=op,
        child_of=parent_span
    )

    outbound_span.set_tag('http.url', request.full_url)
    service_name = request.service_name
    host, port = request.host_port
    if service_name:
        outbound_span.set_tag(tags.PEER_SERVICE, service_name)
    if host:
        outbound_span.set_tag(tags.PEER_HOST_IPV4, host)
    if port:
        outbound_span.set_tag(tags.PEER_PORT, port)

    http_header_carrier = {}
    opentracing.tracer.inject(
        span_context=outbound_span,
        format=Format.HTTP_HEADERS,
        carrier=http_header_carrier)

    for key, value in http_header_carrier.iteritems():
        request.add_header(key, value)

    return outbound_span

Development

virtualenv env
. ./env/bin/activate
make bootstrap
make test

virtualenv env
. ./env/bin/activate
make bootstrap
make docs

pip install zest.releaser[recommended]
prerelease
release
git push origin master --follow-tags
python setup.py sdist upload -r pypi upload_docs -r pypi
postrelease
git push