This example demonstrates how to use OpenTelemetry to instrument an Express application and send traces and metrics to Logfire.

To run the example locally, you need a Logfire account and a project and a local installation of Node 20. If you don't have a Logfire account, create a free one in Logfire.

Clone the repository:

git clone https://github.com/pydantic/logfire.git

cd into the example directory, ensure you're using version 20.17.0 of node, and install:

cd examples/javascript/express
npm install

Then, add an .env file with your Logfire token and configuration:

# Used for reporting traces to Logfire
LOGFIRE_BASE_URL=https://logfire-api.pydantic.dev/
# The write token for your project
LOGFIRE_WRITE_TOKEN=your-write-token
EXPRESS_PORT=8080

Afterwards, you can start the example with npm run start and issue a network request to http://localhost:8080/rolldice using curl, for example:

curl http://localhost:8080/rolldice

If everything is set up correctly, you should see the response from the server and traces reported in Logfire.

The OpenTelemetry configuration is defined in the instrumentation.ts file, where OTLPMetricExporter and OTLPTraceExporter are created and used to send traces and metrics to Logfire. You can add more instrumentation to your application by following the OpenTelemetry documentation.