Multiple absinthe namespaces

[maxsalven]

Describe the bug

If you have multiple graphql endpoints, setting a custom namespace doesn't work.

To Reproduce

I have two graphql endpoints, /api/graphql/user and /api/graphql/admin

  scope "/api/graphql/admin" do
    pipe_through [
      MyAppWeb.GraphqlAdmin.Plug.AppsignalNamespace,
    ]

    forward("/", MyAppWeb.Plug.AbsintheAdmin,
      schema: MyAppWeb.GraphqlAdmin.Schema
    )
  end

defmodule MyAppWeb.GraphqlAdmin.Plug.AppsignalNamespace do
  def init(default), do: default

  def call(conn, _) do
    Appsignal.Span.set_namespace(Appsignal.Tracer.root_span(), "graphql_admin")
    conn
  end
end

Calls to /api/graphql/admin still end up in the graphql namespace.

This line seems to be responsible:
https://github.com/appsignal/appsignal-elixir/blob/main/lib/appsignal/absinthe.ex#L55

Could you modify it to conditionally apply the namespace only if it's currently set to the default?

[jeffkreeftmeijer]

Hey @maxsalven!

Thanks for raising this issue. I've taken a look at the code you posted, and it looks like you're spot on. The Absinthe integration sets the span's namespace whenever it's started. Your plug runs before the Absinthe span is started, so it doesn't set a namespace if no root span has been started.

One way to resolve this is to set the namespace after the span has been started. For example, you could set the namespace while resolving the request or requesting data from the database.

We can't currently conditionally apply the namespace, because we pass the namespace to the agent immediately. That being a one-way data pipeline, we can't determine if the namespace has been set previously.