OpenTelemetry guide for Flask and SQLAlchemy

In this article, you will learn how to use OpenTelemetry with Uptrace to monitor Flask and SQLAlchemy performance.

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• What is tracing?
• What is OpenTelemetry?
• Creating spans
• What is Uptrace?
• Example application
• Configuring OpenTelemetry
• Instrumenting Flask app
• Instrumenting SQLAlchemy
• Running the example
• What's next?

What is tracing?

OpenTelemetry tracing allows to observe requests as they propagate through distributed systems, especially those built using a microservices architecture.

Tracing provides insights into your app performance along with any errors and logs. You immediately see what conditions cause errors and how particular error affects app performance.

Using tracing, you can break down requests into spans. Span is an operation (unit of work) your app performs handling a request, for example, a database query or a network call.

Trace is a tree of spans that shows the path that a request makes through an app. Root span is the first span in a trace.

To learn more about tracing, see Distributed Tracing using OpenTelemetry.

What is OpenTelemetry?

OpenTelemetry is an open-source observability framework for OpenTelemetry tracing (including logs and errors) and OpenTelemetry metrics.

Otel allows developers to collect and export telemetry data in a vendor agnostic way. With OpenTelemetry, you can instrument your application once and then add or change vendors without changing the instrumentation, for example, here is a list popular DataDog alternatives that support OpenTelemetry.

OpenTelemetry is available for most programming languages and provides interoperability across different languages and environments.

Creating spans

To measure performance of database queries or HTTP requests, you can create a span using OpenTelemetry Python API:

from opentelemetry import trace

tracer = trace.get_tracer("app_or_package_name", "1.0.0")

def some_func(**kwargs):
    with tracer.start_as_current_span("some-func") as span:
        // the code you are measuring

To record contextual information, you can annotate spans with attributes. For example, an HTTP endpoint may have such attributes as http.method = GET and http.route = /projects/:id.

# To avoid expensive computations, check that span is recording
# before setting any attributes.
if span.is_recording():
    span.set_attribute("http.method", "GET")
    span.set_attribute("http.route", "/projects/:id")

You can also record exceptions and set the span status code to indicate an error:

except ValueError as exc:
    # Record the exception and update the span status.
    span.record_exception(exc)
    span.set_status(trace.Status(trace.StatusCode.ERROR, str(exc)))

See OpenTelemetry Python tracing for details.

What is Uptrace?

Uptrace is an open source APM for OpenTelemetry with an intuitive query builder, rich dashboards, automatic alerts, and integrations for most languages and frameworks.

You can get started with Uptrace by downloading a DEB/RPM package or a pre-compiled Go binary.

Example application

In this tutorial, you will be instrumenting a toy app that uses Flask and SQLAlchemy database client. You can retrieve the source code with the following command:

git clone git@github.com:uptrace/uptrace.git
cd example/flask

The app comes with some dependencies that you can install with:

pip install -r requirements.txt

Configuring OpenTelemetry

Uptrace provides OpenTelemetry Python distro that configures OpenTelemetry SDK for you. To install the distro:

pip install uptrace

Then you need to initialize the distro whenever you app is started, for example, in manage.py:

# manage.py

import uptrace

def main():
    uptrace.configure_opentelemetry(
        # Copy DSN here or use UPTRACE_DSN env var.
        # dsn="",
        service_name="myservice",
        service_version="v1.0.0",
    )

    # other code

See documentation for details.

Instrumenting Flask app

To instrument Flask app, you need to install a corresponding OpenTelemetry Flask instrumentation:

pip install opentelemetry-instrumentation-flask

Then you can instrument the Flask app:

from opentelemetry.instrumentation.flask import FlaskInstrumentor

app = Flask(__name__)
FlaskInstrumentor().instrument_app(app)

Instrumenting SQLAlchemy

To instrument SQLAlchemy database client, you need to install a corresponding instrumentation:

pip install opentelemetry-instrumentation-sqlalchemy

Then instrument the db engine:

from flask_sqlalchemy import SQLAlchemy
from opentelemetry.instrumentation.sqlalchemy import SQLAlchemyInstrumentor

app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///:memory:"
db = SQLAlchemy(app)
SQLAlchemyInstrumentor().instrument(engine=db.engine)

Running the example

You can start Uptrace backend with a single command using Docker example:

docker-compose up -d

And then start the app passing Uptrace DSN as an env variable:

export UPTRACE_DSN=http://project2_secret_token@localhost:14317/2
python3 main.py

The app should be serving requests on http://localhost:8000 and should render a link to Uptrace UI. After opening the link, you should see this:

What's next?

Next, you can learn about OpenTelemetry Python API to create your own instrumentations or browse existing instrumentations provided by the community.