OTEP: Allow multiple Resources in an SDK

[jsuereth]

Alternative to #4316 -

We propose allowing {Signal}Provider to be exended with additional Entity, instead of allowing Resource to be mutable as a forward path for modelling "session" in browsers/devices. Additionally, we believe this will help with multi-tenant telemetry use cases.

E.g. This OTEP proposes the following

const sessionEntity: Entity = discoverSessionEntity();
// SDK has created an isolated meterprovider for this session.
const meterForSession = meterProvider.forEntity(sessionEntity).getMeter("my meter"); 
const latencyForSession = meterForSession.getHistogram("latency", ...);
latencyForSession.record(...); // Record latency against session.

instead of:

const meter = meterProvider.getMeter("my meter");
const latency = meter.getHistogram("latency", ...);
const sessionEntity: Entity = discoverSessionEntity();
// On resource mutation, metrics must be flushed and/or new allocation for all metrics created.
entityProvider.addOrReplace(sessionEntity);  
latency.record(...); // Record latency against session.

[tigrannajaryan]

Does this OTEP imply removing EntityRefs from the Resource in proto?

[tigrannajaryan]

I like this direction.

[jsuereth]

Does this OTEP imply removing EntityRefs from the Resource in proto?

No. EntityRef in resource would interact with Entity on InstrumentationScope, and we need to sort out how.

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This PR was marked stale due to lack of activity. It will be closed in 7 days.

[github-actions[bot]]

This PR was marked stale due to lack of activity. It will be closed in 7 days.

[github-actions[bot]]

Closed as inactive. Feel free to reopen if this PR is still being worked on.

[dashpole]

Go prototype: https://github.com/open-telemetry/opentelemetry-go/pull/7723. I took some creative liberties, but the idea of an entity-bound provider works in the Go SDK from what I can tell.

My main realization is that we can't include the Bind function in the API since it would add a dependency on resource, which is part of the SDK.