basic-metrics-example

Basic Example of OpenTelemetry Metrics on Fastly Compute

This is an example of using @fastly/compute-js-opentelemetry, an implementation of the OpenTelemetry JavaScript API for Compute.

Run the example

You will need Node.js (>= 18) and Fastly CLI (>= 9.x).

This example will export metrics to a local instance of an OpenTelemetry Collector. It has been tested with OpenTelemetry Collector Demo.

First, build compute-js-opentelemetry.

Clone fastly/compute-js-opentelemetry and build it:

git clone https://github.com/fastly/compute-js-opentelemetry.git
cd compute-js-opentelemetry
npm install
npm run build

Next, move to this subdirectory, and build this example:

cd examples/basic-tracing-example
npm install
fastly compute build

To run this example locally:

fastly compute serve

TODO: If you would like to deploy this to Fastly, then you will have to make modifications.

Description

This simple example shows the instantiation of the following objects:

• OTLPMetricExporter
  an OpenTelemetry Metric Exporter adapted for use in a Compute handler.

• FastlyMetricReader
  an OpenTelemetry Metric Reader adapted for use in a Compute handler.

• FastlySDK
  an optional class that simplifies the initialization and coordination of the OpenTelemetry objects.

• DiagConsoleLogger (@opentelemetry/api)
  standard logger that outputs debug messages to the console.

Beyond this, this is a basic Compute JavaScript application. A fetch handler is registered using the addEventListener() function, which receives an event object. The application responds by running handleRequest, which takes the event object and generates a Response object (or Promise that resolves to one).

Additionally, this example application will count the number of requests that were made to it. To do this, it needs to import the metrics object exported from @opentelemetry/api. It obtains a meter named my-meter from the default meter provider, then creates a Counter named requests. It then adds 1 to the counter, along with the path as an attribute. The metric queued for sending to the backend, and is sent when the application lifecycle ends.

Note that all the initialization of OpenTelemetry can be kept completely separate from the application logic, by placing it in a separate file (the ./telemetry.js file in this example).