Feature Request: Support for Apollo Federation in Tailcall

[amitksingh1490]

Summary

Enable Tailcall to support Apollo Federation by adding a flag in the @server directive. When enabled, this flag will support the _entities query, allowing Tailcall to function as a subgraph in a federated architecture.

Detailed Description

To integrate Apollo Federation with Tailcall, we propose the following enhancements:

1. Flag Addition in @server:

   • Introduce a new flag within the @server directive to enable federation support.
   • When this flag is activated, Tailcall will automatically handle the _entities query, essential for Apollo Federation's distributed schema architecture.

2. Support for Resolver Directives on Types:

   • Enable resolver directives like @http, @grpc, @const, and others to be applied directly on Types.
   • This will allow Tailcall to infer the key fields required for federation based on the resolver configuration.

3. Key Inference:

   • Analyze the resolvers attached to Types and automatically infer the appropriate @key directive.
   • Example:
     • For @http(path: "/users/{{.value.id}}"), the inferred key would be @key(fields: "id").
     • For the query:

       @http(path: "/users/", query: [
         {key: "id", value: "{{.value.id}}"},
         {key: "name", value: "{{.value.name}}"},
         {key: "org_id", value: "{{.value.organisation.id}}"},
         {key: "org_name", value: "{{.value.organisation.name}}"}
       ])
       

       The inferred key would be @key(fields: "id name organisation {id, name}").
   • If multiple resolvers are attached to the same type, multiple keys will be inferred and handled accordingly.

4. Support for _entities Query:

   • Implement the _entities query required by Apollo Federation.
   • Example of how the query to the subgraph would look:

     type Query {
       _entities(representations: [_Any!]!): [_Entity]!
     }
     

     • Example query:

       query ($representations: [_Any!]!) {
         _entities(representations: $representations) {
           ... on User {
             id
             username
           }
         }
       }
       

       • Corresponding variable:

         {
           "representations": [
             {
               "__typename": "User",
               "id": "5"
             }
           ]
         }
         

References

• For a reference implementation of Apollo Federation, see the async-graphQL implementation.

• Subgraph Documentation

Technical Requirements

• Integration & Unit Tests are required.
• Update the documentation on website