Example of how the new RequestTracing might be used to send the proper metrics at each request and interpose some header

metrics_client.py

class MetricsClient(ClientSession):
    def __init__(self, metric_name, region, **kwargs):
        self(MetricsClient, self).__init__(
            self,
            *args,
            request_tracing=True,
            request_tracing_ctx=dict
            **kwargs)

        self.metric_name = metric_name
        self.region = region

        self.on_request_start.add(self._request_started)
        self.on_request_stop.add(self._request_finished)
        self.on_request_exception.add(self._request_error)

    async def _request_started(self, session, trace_context, method, host, port, headers):
        trace_context.started = self._loop.time()

        # save some information related to request that will be used
        # to send as tags along the  metrics
        trace_context.host = host
        trace_context.port = port
        trace_context.method = method

        # modify heades to forward request_id
        headers['request_id'] = aiotask_context.get('request_id')

    async def _request_finished(self, session, trace_context, response):
        elapsed = self._loop.time() - trace_context.started

        await metric.increment(
            self.metric_name, 
            # tags composed from different sources
            status_code=resopnse.status_code,
            region=self.region,
            query=trace_context.query
        )

        await metric.time(
            self.metric_name,
            elapsed,
            # tags time series
            status_code=resopnse.status_code,
            region=self.region,
            host=trace_context.host,
            port=trace_context.port,
            method=trace_context.method,                       
            query=trace_context.query
        )
        
    async def _request_exception(self, session, trace_context, exc):
        status_code = 503 if isinstance(exc, asyncio.TimeoutError) else 500
        await metric.increment(
            self.metric_name, 
            status_code=status_code,  
        )



session = MetricClient('foo_metric', 'eu-west-1')

async def foo():
    resp = await session.get(
        "http://microservice_foo.local/search?q=people",
        trace_trace_context=SimpleNamespace(query='people')
    )