[roskilli]

> Moreover, we encountered some rough edges in the metrics-related functionality of the Go SDK referenced above. Ultimately, we had to write a conversion layer on top of the OTel metrics API that allowed for simple, Prometheus-like counters, gauges, and histograms.

Have encountered this a lot from teams attempting to use the metrics SDK.

Are you open to comment on specifics here and also what kind of shim you had to put in front of the SDK? It would be great to continue to retrieve feedback so that we can as a community have a good idea of what remains before it's possible to use the SDK for real world production use cases in anger. Just wiring up the setup in your app used to be fairly painful but that has gotten somewhat better over the last 12-24 months, I'd love to also hear what is currently causing compatibility issues w/ the metric types themselves using the SDK which requires a shim and what the shim is doing to achieve compatibility.

[bhyolken]

Sure, happy to provide more specifics!

Our main issue was the lack of a synchronous gauge. The officially supported asynchronous API of registering a callback function to report a gauge metric is very different from how we were doing things before, and would have required lots of refactoring of our code. Instead, we wrote a wrapper that exposes a synchronous-like API: https://gist.github.com/yolken-airplane/027867b753840f7d15d6....

It seems like this is a common feature request across many of the SDKs, and it's in the process of being fixed in some of them (https://github.com/open-telemetry/opentelemetry-specificatio...)? I'm not sure what the plans are for the golang SDK specifically.

Another, more minor issue, is the lack of support for "constant" attributes that are applied to all observations of a metric. We use these to identify the app, among other use cases, so we added wrappers around the various "Add", "Record", "Observe", etc. calls that automatically add these. (It's totally possible that this is supported and I missed it, in which case please let me know.)

Overall, the SDK was generally well-written and well-documented, we just needed some extra work to make the interfaces more similar to the ones we were using before.

[roskilli]

Thanks for the detailed response.

I am surprised there is no gauge update API yet (instead of callback only), this is a common use case and I don't think folks should be expected to implement their own. Especially since it will lead to potentially allocation heavy bespoke implementations, depending on use case given mutex+callback+other structures that likely need to be heap allocated (vs a simple int64 wrapper with atomic update/load APIs).

Also I would just say that the fact the APIs differ a lot to more common popular Prometheus client libraries does beg the question of do we need more complicated APIs that folks have a harder time using. Now is the time to modernize these before everyone is instrumented with some generation of a client library that would need to change/evolve. The whole idea of an OTel SDK is instrument once and then avoid needing to re-instrument again when making changes to your observability pipeline and where it's pointed. This becomes a hard sell if OTel SDK needs to shift fairly significantly to support more popular & common use cases with more typical APIs and by doing so leaves a whole bunch of OTel instrumented code that needs to be modernized to a different looking API.

[arccy]

the official SDKs will only support an api once there's a spec that allows it.

for const attributes, generally these should be defined at the resource / provider level: https://pkg.go.dev/go.opentelemetry.io/otel/sdk/metric#WithR...