Is it safe to create a new metric on every request?

[nwalters512]

Background

The JS metrics instrumentation docs say the following:

It’s generally recommended to call getMeter in your app when you need it rather than exporting the meter instance to the rest of your app. This helps avoid trickier application load issues when other required dependencies are involved.

I'm definitely encountering these "trickier application load issues" in my application. I originally created metrics at the top-level scope of my modules. For instance, a small Express router that I might use in my application:

import express from 'express';
import { metrics } from "@opentelemetry/api";

const meter = metrics.getMeter('my-service');
const count = meter.createCounter('events');

const router = Router();
router.get('/', (req, res, next) => {
  count.add(1);
  res.send(204);
});
export default router;

However, due to the way the meter etc. are configured (I need to asynchronously load config to know if it's enabled and which exporter to use, and I also need to asynchronously detect resource attributes for the MeterProvider), metrics.setGlobalMeterProvider(...) wouldn't have been called before the above call to metrics.getMeter(), so my metrics weren't being captured or exported.

Question

Is it safe to change the above code to the following?

import express from 'express';
import { metrics } from "@opentelemetry/api";

const router = Router();
router.get('/', (req, res, next) => {
  const meter = metrics.getMeter('my-service');
  const count = meter.createCounter('events');
  count.add(1);
  res.send(204);
});
export default router;

This would match my reading of "call getMeter in your app when you need it", and from reading the source code, it looks as though multiple metrics with the same name will share the same state. I think this will do what I want, and in testing it appears to behave as expected.

If this isn't considered a best practice, I'd love to hear recommendations about how to handle a MeterProvider that has to be created asynchronously on application startup.

[legendecas]

Meters and metric instruments are safe to be retrieved multiple times with identical configurations (names, types, etc.). However, it is still recommended to keep a reference to their instances as de-duplication comes with performance penalties.