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Azure Application Insights, FastAPI, and tracing

Debugging is difficult, what’s even more difficult, debugging production apps. Live production apps.

There are tools designed for this purpose. Azure has Application Insights, product that makes retracing history of events easier. When setup correctly you may go from a http request down to a Db call with all the query arguments. Pretty useful and definitely more convenient than sifting through log messages.

Application Insights console with end-to-end transaction details

Here you can see the exact query that had been executed on the database.

Application Insights console with SQL query details

You may also see every log related to a particular request in Log Analytics.

Application Insights logs with a query displaying only relevant logs

Improving your work life like this is pretty simple. Everything here is done using opencensus and it’s extensions. Opencensus integrates with Azure pretty nicely. First thing to do is to install required dependencies.

# pip 
pip install opencensus-ext-azure opencensus-ext-logging opencensus-ext-sqlalchemy opencensus-ext-requests

# pipenv

pipenv install opencensus-ext-azure opencensus-ext-logging opencensus-ext-sqlalchemy opencensus-ext-requests

# poetry

poetry add opencensus-ext-azure opencensus-ext-logging opencensus-ext-sqlalchemy opencensus-ext-requests

Next step is to activate them by including a couple of lines in your code. Here I activate 3 extensions, logging, requests, and sqlalchemy. Here is a list of other official extensions.

import logging

from opencensus.trace import config_integration
from opencensus.ext.azure.log_exporter import AzureLogHandler

logger = logging.getLogger(__name__)
config_integration.trace_integrations(["logging", "requests", "sqlalchemy"])

handler = AzureLogHandler(
    connection_string="InstrumentationKey=YOUR_KEY"
)
handler.setFormatter(logging.Formatter("%(traceId)s %(spanId)s %(message)s"))
logger.addHandler(handler)

One last thing is a middleware that will instrument every request. This code is taken from Microsoft’s documentation.

@app.middleware("http")
async def middlewareOpencensus(request: Request, call_next):
    tracer = Tracer(
        exporter=AzureExporter(
            connection_string="InstrumentationKey=YOUR_KEY"
        ),
        sampler=ProbabilitySampler(1.0),
    )
    with tracer.span("main") as span:
        span.span_kind = SpanKind.SERVER

        response = await call_next(request)

        tracer.add_attribute_to_current_span(
            attribute_key=HTTP_STATUS_CODE, attribute_value=response.status_code
        )
        tracer.add_attribute_to_current_span(
            attribute_key=HTTP_URL, attribute_value=str(request.url)
        )

    return response

You are done 🙂 you will not loose information on what is going on in the app. You will be quicker in finding problems and resolving them. Life’s good now.

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