stats/exporters/ocagent: implement exporter

[odeke-em]

Currently we've only got the ocagent trace exporter. It would be nice to have once for stats too so that we can start to use the OpenCensus Agent.

I see #454 open but that issue will involve doing a bunch of double work since it is almost rewriting those exporters. With the ocagent exporter converts stats aka view_data to OpenCensus Proto Metrics, folks can then switch over to just using the agent.

I am coming here as I am currently writing the guide for the new OpenCensus Redis-Py wrapper https://pypi.org/project/ocredis/ and it works great with the Trace exporter i.e.

#!/usr/bin/env python

import ocredis

from opencensus.trace.tracer import Tracer
from opencensus.trace.exporters.ocagent.trace_exporter import TraceExporter
from opencensus.trace.samplers import always_on
from opencensus.common.transports import async_

def create_opencensus_exporters_and_tracer():
    # Create the ocagent-exporter that'll upload our traces
    # to the OpenCensus Agent.
    octe = TraceExporter(service_name='pysearch', transport=async_.AsyncTransport)

    tracer_init_args = dict(exporter=octe,
            # Always sampling for demo purposes.
            sampler=always_on.AlwaysOnSampler())

    return tracer_init_args

def main():
    r = ocredis.OcRedis(host='localhost', port=6379, db=10)
    tracer_init_args = create_opencensus_exporters_and_tracer()
    while True:
        query = raw_input('$ ')
        response = do_search(r, query, **tracer_init_args)
        print('> ' + response + '\n')

def do_search(client, query, **tracer_init_kwargs):
    tracer = Tracer(**tracer_init_kwargs)
    with tracer.span('Search') as span:
        span.add_annotation('Searching', query=query)

        # Check Redis if we've already memoized the response.
        response = client.get(query)

        if response is not None: # Cache hit
            span.add_annotation('Cache hit', store='redis', client='redis-py')
            print('Cache hit! Now deleting it to make for a cache miss later')
            # Clear the response so that the next search will return a cache-miss.
            client.delete(query)

        else:  # Cache miss
            span.add_annotation('Cache miss', store='redis', client='redis-py')
            print('Cache miss! Now processing and memoizing it to make for a cache hit later')

            # Now process the result and memoize it.
            response = query.upper()
            client.set(query, response)

        span.finish()
        return response

if __name__ == '__main__':
    main()

but after writing that, I came over to use the ocagent-stats exporter but didn't find any.

[c24t]

Fixed in #617.