django-zipkin 0.0.3

Getting the data to Zipkin

From here you it’s up to you to get the messages to Zipkin. Here’s how we do it at Prezi:

• We configure logging in each service using django-zipkin to send log messages from the zipkin logger to the locally running Scribe instance, into the category zipkin.

• The Scribe instances are configured to forward the zipkin category directly to the Zipkin collector. This is useful because Scribe buffers messages in case the collector (or the network to it) is down.

Another alternative may be logging to syslog, and using scribe_apache shipped with Scribe to send data to Zipkin (possibly via a local Scribe server).

Recording annotations

django-zipkin creates a single span per served requests. It automatically adds a number of annotations (see below). You can also add your own annotations from anywhere in your code:

from django_zipkin.api import api as zipkin_api

zipkin_api.record_event('MySQL: "SELECT * FROM auth_users"', duration=15000)  # Note duration is in microseconds, as defined by Zipkin
zipkin_api.record_key_value('Cache misses', 15)  # You can use string, int, long and bool values

Propagating tracing information

To identify which spans belong to the same trace, some information must be passed on with inter-service calls. django-zipkin provides facilities for this on both the client and the server side. The middleware automatically reads the trace propagation HTTP headers described in the Zipkin documentation. For propagating data to outgoing requests, a function returning a dict of the correct HTTP headers is provided:

from django_zipkin.api import api as zipkin_api
headers = zipkin_api.get_headers_for_downstream_request()

# During a request returns something like this:
{'X-B3-Sampled': 'false', 'X-B3-TraceId': 'b059fb34103a46f7', 'X-B3-Flags': '0', 'X-B3-SpanId': 'a42f4f3a045c54a5'}

Automatically generated annotations

sr and ss annotations are automatically added by the middleware. The following binary (key-value) annotations are also added:

It’s up to you to add cs and cr (client send and client receive) annotations in whatever client you use.

Middleware order

If a middleware above django-zipkin returns a response, then the request processing part of django-zipkin will never be called, resulting in an inconsistent internal state. In this case your custom annotations and most of the automatically added annotations will be lost, and timing information will be incorrect. An extra annotation will be added with the following value:No ZipkinData in thread local store. This can happen if process_request didn't run due to a previous middleware returning a response. Timing information is invalid.

View wrappers

If your view is wrapped (for example with a decorator) without using the functools.wraps decorator, then django-zipkin has no way of retrieving the name of the view. In this case django.view.func_name will be the function name of the wrapper function. This is something you’ll want to avoid in your own code.

One offender is Tastypie: django.view.func_name will always be wrapper. On requests served by Tastypie the annotation django.tastypie.resource_name will be added with the name of the Tastypie resource, and django.url_name will be something useful like api_dispatch_list.

Zipkin UI vs. JSON annotation values

The django.view.kwargs annotation has a JSON string as its value for easier automated processing. Unfortunately this make the UI display the value as [object Object]. See Zipkin issue #410 for any progress on this. If you want to find the value on the web UI, you can open the page source and search for django.view.kwargs.

Settings variables

ZIPKIN_SERVICE_NAME: Default None. The service name that will appear on Zipkin (the service_name value in the sent Thrift objects).

ZIPKIN_LOGGER_NAME: Default 'zipkin'. The name of the logger to use when sending Zipkin messages through the Python logging system.

ZIPKIN_DATA_STORE_CLASS: Default 'django_zipkin.data_store.ThreadLocalDataStore'. django-zipkin needs to pass some data from the request processor to the response processor. This same data needs to be accessible from anywhere in the users code. The default implementation for this is to use thread-local storage. gevent and greenlet monkey-patch it, so this implementation works fine even under gunicorn and friends. You can provide your own implementation - it needs to implement the methods of django_zipkin.data_store.BaseDataStore.

ZIPKIN_ID_GENERATOR_CLASS: Default 'django_zipkin.id_generator.SimpleIdGenerator'. The class used to generate span and trace ids if we don’t get one from the incoming request.

Configglue

configglue support is provided via django_zipkin.schema; you can include it into your own schema like this:

from django_zipkin.schema import DjangoZipkinSection


class MySchema(...):
   ...
   class zipkin(DjangoZipkinSection):
       pass