Automatic tracing of express

[vmarchaud]

Is it applicable for Node or Browser or both
Node only

Do you expect this plugin to be commonly used
Weekly Downloads: 6M (https://www.npmjs.com/package/express)

What version of plugin are you interested in using
Versions: 4

Additional context

• Is there a reference you could point for the well-defined lifecycle methods
  Opencensus-style instrumentation that i've implemented before: https://github.com/keymetrics/pm2-io-apm/blob/master/src/census/plugins/express.ts

Implementation of datadog: https://github.com/DataDog/dd-trace-js/tree/master/packages/datadog-plugin-express

[dyladan]

What do you think would be gained beyond the http information already available? Are we better off auto-instrumenting it or just exporting a middleware that uses the API?

[OlivierAlbertini]

What do you think would be gained beyond the http information already available?

You can get the route attribute.

I have already done an express plugin internally for OpenTelemetry and I don't see a real advantage to have it in this repo (I'm not against to have it too)... I did it because some packages like body-parser seems to clear the scope... So I bind the middleware after body-parser to recreate it if this happens. You can also create an error middleware where you can add the detailed error to the span...

I think the express plugin is more useful for customizing the span.

[dyladan]

dropping scope is a big deal so that sounds like a good win for us. can you work with @vmarchaud since you already made an internal version?

[vmarchaud]

@OlivierAlbertini I didn't had the issue with my OC plugin, that's weird.

@dyladan That was a common request back when i worked at @keymetrics to allow customers to aggregate by the route (since it's common to have an id in urls). Also useful to pinpoint if you have a sync middleware (like auth with jwt) taking a lot of time.

dropping scope is a big deal so that sounds like a good win for us

I'm not sure to understand since it was dropping the scope it should fail to create child spans afterward, i don't see why it's a good win ^^

[dyladan]

@vmarchaud let me rephrase. If the scope is being dropped, and creating a plugin can prevent it from being dropped, then that sounds like a good win.

[vmarchaud]

@dyladan Got it, indeed its important in that case.

[OlivierAlbertini]

@OlivierAlbertini I didn't had the issue with my OC plugin, that's weird.

Currently we have Opencensus and OpenTelemetry in our environnement and we have the issue with OpenCensus "0.0.19" for sure and OpenTelemetry "0.1.1".

It doesn't happens every time (it's really hard to reproduce) and I don't know how the body parser works but having a middleware after have fixed the issue. I flagged those spans differently in order to see if there is a pattern...

@dyladan, yes I can work with @vmarchaud. I can make a draft PR and request a review (@vmarchaud ) but you can create a PR too since you made the issue and I can review it... As you want @vmarchaud, you decide ^^