Allow for Scatter-Gather Requests

[zackerydev]

Hello! 👋

I am having a great time at Apollo Summit so far! And I've been loving trying out the new router. I have a somewhat complex problem that I am trying to achieve with the new Apollo Router and I will try to explain it with an app I've been testing out called "Alexandria".
This is the public studio link
https://studio.apollographql.com/public/alexandria-supergraph/home?variant=prod

This my Supergraph, the router is running on GraphOS and the individual services are fly.io apps here:

https://alexandria-profiles.fly.dev/ (Has one user: me!)
https://alexandria-profiles-eu.fly.dev/ (Has one user named "British Guy")

Notably, these two graphs are identical

The purpose of these two graphs is to store user PII in a specific geography. EU users exist in a fly.dev app in London, and US users exist in a fly.dev app in the USA.

What I would like is for users of the supergraph to be able to run:

{
  profiles {
    firstName
  }
}

And get back this object:

{
  "data": {
    "profiles": [
      {
        "firstName": "Zackery"
      },
      {
         "firstName": "British"
      }
    ]
  }
}

I am very new to Rust, and I'm not sure if this would be possible with a native router feature. There are a couple considerations here:

• Your query will be as slow as the slowest subgraph (this is ok)
• Optionally turning this on with a directive, maybe like @broadcast or @global directive that says to aggregate results across
• I'm not sure if it was supposed to work but I was able to use rover to register the eu URL since it has the exact same schema. I think this feature would only be doable in that instance.

Obviously there might be better patterns around this which I am open to learning about as well. The lack of this feature is causing us to struggle with adopting Federation across our globally replicated data-centers. We have to keep all this data separate for compliance reasons.

Someone at Apollo Summit mentioned to make Discussions before trying to implement it ourselves. I don't know enough Rust to know if this is even a plugin I should invest time into but I'm curious what everyone in the community's thoughts are!