Context and Baggage API usage

[arielvalentin]

I am interested in taking in using the Context and Baggage API in our applications however I want to ensure I am doing so in an idiomatic way.

I can see that the API provides utility methods like OpenTelemetry::Context.with_current that changes the implicit reference in OpenTelemetry::Context.current.

The OpenTelemetry::Baggage::Manager also generates a new instance of the OpenTelemetry::Context that has a newly populated baggage entry, defaulting to using the implicit context. e.g. OpenTelemetry::Baggage::Manager#build

I also see examples in auto-instrumented libraries that set the implicit scope using OpenTelemetry::Context.with_value, but haven't seen any used for Baggage just yet.

Would this be the idiomatic way to do so?

updated_context = OpenTelemetry.baggage.build do |builder|
  builder.set_value(key_a: "foo")
  builder.set_value(key_b: "bar")
end

Context.with_current(updated_context) do
   # application code goes here.... 
end

[mwear]

@arielvalentin your example is idiomatic given the current API. The Baggage::Manager helps to manipulate baggage in a context, and then the Context API is used to activate / deactivate a given context instance.

Also, given that you are starting to look at using baggage, you might have some opinions on #703.

[arielvalentin]

I think that the parts here that stand out to me are that the baggage convenience method is not referring to a concept or role named Baggage but rather the BaggageManager, which appears to also be a global variable whose state changes as a result of also changing the implicit Context.current value.

I am not certain if this will make things better, but perhaps if the APIs were symmetric it may reduce what I perceive as friction:

OpenTelemetry::Context.with_baggage( key_a: "foo". key_b: "bar" ) do |ctx|
    # your application code goes here
end

or

OpenTelemetry.baggage.with_baggage( key_a: "foo". key_b: "bar" ) do |ctx|
    # your application code goes here
end

The latter seems off to me because again we do not really have a notion of a Baggage, it is a special key in the Context so I lean towards the former, but I think that we may be constrained here by the official API.

[ahayworth]

I almost feel like it would look more idiomatic if it read as:

updated_context = OpenTelemetry.baggage.merge do |context|
  context.set_value(key_a: "foo")
  context.set_value(key_b: "bar")
end

...primarily since merge with a block is something that at least vaguely mimics the Enumerable module (granted: this merge is not what Enumerable#merge really does... but hopefully my point makes it across regardless - maybe s/merge/update/, instead).