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Building Federated GraphQL APIs using Flask Adarsh Divakaran

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REST vs GraphQL

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REST API URL: localhost:8000/api/v1 Req: GET /greeting Resp: {“greeting” : “hello”}

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GraphQL

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REST

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GraphQL

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GraphQL Features

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Single Endpoint REST GraphQL

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Operations REST GET: Fetch data POST, PUT, PATCH, DELETE: Add, edit, modify and delete operations GraphQL HTTP Method used is POST always. QUERY: Fetch data MUTATION: Modify, update, delete, etc. SUBSCRIPTION: Realtime persistent operations

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Strong Typing

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Scalars & Types in GraphQL ● Int A signed 32‐bit integer. ● Float A signed double-precision floating-point value. ● String A UTF‐8 character sequence. ● Boolean true or false. ● ID The ID scalar type represents a unique identifier Other types/containers: List, NonNull, Enum, Union, Interface (source: graphql.org)

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Scalars & Types in GraphQL Enumeration enum Episode { NEWHOPE EMPIRE JEDI } Custom type type Character { name: String! appearsIn: [Episode]! } Union type union SearchResult = Human | Droid | Starship

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Advantages of GraphQL

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Overfetching Prevention Initial API Version Return a greeting message New Requirement For desktop web clients, return a greeting image along with the greeting message

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Overfetching Prevention REST - Initial Version

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Overfetching Prevention REST - Option 1 Disadvantage: For mobile clients, an extra unused field is returned with the response

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Overfetching Prevention REST - Option 2 - Adding separate endpoint Disadvantage: Extra network call and complexity for web clients

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Overfetching Prevention GraphQL Solution Query of Mobile client

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Overfetching Prevention GraphQL Solution - Desktop client GraphQL allows us to query only the fields we need

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Introspection & Type system ● Strongly typed and schema based ● All supported operations by a server are returned by ‘introspection’ ● Presence of tooling to auto generate client code ● REST would require additional doc tools - ‘flasgger’ or ‘flask-rest-api’. ● GraphQL development is centered around its schema

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Choosing a GraphQL Server

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Schema First vs Code First Code First Schema First

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Demo

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GraphQL Federation

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Apollo Federation ● A standard/spec for combining multiple independent GraphQL schemas ● Combines multiple related schemas from microservices (subgraphs) to a single unified schema (supergraph) ● Abstracts away the microservice design from clients

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When to use GraphQL & Federation ● Use GraphQL where it shines - Example: internal APIs with diverse use cases ● Use GraphQL Federation when it fits your architecture / when a monolith becomes unmanageable [ From “8 Years of GraphQL: Unraveling the Trade-Offs” Talk by Marc-Andre Giroux (GraphQL Conf 2023) ]

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Federation - Concepts

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Directives A directive decorates part of a GraphQL schema or operation with additional configuration. Denoted using ‘@’ - similar to decorators in Python

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Directives

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Entity ● An Entity in Federation is an object type that can resolve its fields across multiple subgraphs. ● It can be thought of as a GraphQL type which appears across multiple microservice subgraphs.

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Entity - UserType

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@key directive ● Designates an object type as an entity. ● The @key directive is used to indicate fields that can be used to uniquely identify and fetch an object.

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Federation Gateway/Router ● Combines multiple microservice schemas and exposes a single combined endpoint ● Intelligent - It holds the logic to resolve entities and shared types

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Reference resolver function The reference resolver function enables the Federation gateway's query planner to resolve a particular entity by its @key fields.

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Demo

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References ● Graphql Specification: https://spec.graphql.org/ ● Graphql.org Docs: https://graphql.org/learn/ ● Apollo Federation Docs: https://www.apollographql.com/docs/federation/ ● Strawberry GraphQL Docs: https://strawberry.rocks/docs ● 8 Years of GraphQL: Unraveling the Trade-Offs: Marc-Andre Giroux

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Thank You adarsh-d adarshd905 Slides and Demo code: go.adarsh.pizza/flaskcon