Gateway composition in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Gateway Composition in GraphQL?

Gateway Composition is a method to combine multiple GraphQL services into one unified API, allowing clients to query data from different sources through a single endpoint.

beginner

How does Gateway Composition improve client experience?

It simplifies client requests by providing a single GraphQL endpoint that aggregates data from multiple services, so clients don't need to manage multiple APIs separately.

intermediate

What role does a Gateway play in Gateway Composition?

The Gateway acts as a central server that receives client queries, splits them into sub-queries for different services, then combines the results into one response.

intermediate

Name one challenge Gateway Composition helps to solve.

It helps solve the problem of data fragmentation by merging multiple GraphQL schemas into a single schema, making data access easier and more consistent.

advanced

What is a key difference between Gateway Composition and schema stitching?

Gateway Composition focuses on composing multiple GraphQL services at runtime with a gateway, while schema stitching merges schemas statically before serving them.

What does a GraphQL Gateway do in Gateway Composition?

A Combines multiple GraphQL services into one API

B Stores data for all services

C Replaces all backend services

D Only handles authentication

The Gateway combines multiple GraphQL services into a single API endpoint for clients.

Which benefit does Gateway Composition provide to clients?

A Multiple endpoints to query

B Single endpoint for all data

C No need for queries

D Direct database access

Clients use a single endpoint to access data from multiple services.

Gateway Composition typically involves:

A Deleting unused services

B Using only one database

C Replacing REST APIs

D Merging schemas at runtime

Gateway Composition merges multiple GraphQL schemas dynamically at runtime.

Which is NOT a function of the Gateway in Gateway Composition?

A Serving as a single API endpoint

B Combining service responses

C Storing all client data permanently

D Splitting queries to services

The Gateway does not store client data permanently; it routes and combines queries and responses.

Gateway Composition helps to:

A Simplify data access

B Increase client complexity

C Fragment client queries

D Remove GraphQL schemas

It simplifies data access by unifying multiple services under one API.

Explain what Gateway Composition is and why it is useful in GraphQL.

Think about how multiple data sources can be accessed easily by clients.

Describe the role of the Gateway in Gateway Composition and how it handles client queries.

Focus on the Gateway's job as a middleman between clients and services.

Practice

1. What is the main purpose of gateway composition in GraphQL?

easy

A. To combine multiple GraphQL services into a single API endpoint

B. To create multiple endpoints for each service

C. To replace GraphQL with REST APIs

D. To disable client requests

Solution

1. Step 1: Understand gateway composition

   Gateway composition merges several GraphQL services into one unified API.

2. Step 2: Identify the main benefit

   This allows clients to send requests to a single endpoint instead of multiple services.

3. Final Answer:

   To combine multiple GraphQL services into a single API endpoint -> Option A

4. Quick Check:

   Gateway composition = single API endpoint [OK]

Hint: Gateway composition means one API endpoint for many services [OK]

Common Mistakes:

• Thinking it creates multiple endpoints
• Confusing with REST APIs
• Believing it disables client requests

2. Which of the following is the correct way to initialize ApolloGateway with two services named 'users' and 'products'?

easy

A. ApolloGateway({ services: ['users', 'products'] })

B. new ApolloGateway(services: ['users', 'products'])

C. new ApolloGateway({ services: [{ name: 'users', url: 'http://users' }, { name: 'products', url: 'http://products' }] })

D. new ApolloGateway({ endpoints: ['users', 'products'] })

Solution

1. Step 1: Recall ApolloGateway initialization syntax

   ApolloGateway expects an object with a 'services' array containing objects with 'name' and 'url'.

2. Step 2: Match the correct syntax

   new ApolloGateway({ services: [{ name: 'users', url: 'http://users' }, { name: 'products', url: 'http://products' }] }) correctly uses new ApolloGateway with services array of objects including name and url.

3. Final Answer:

   new ApolloGateway({ services: [{ name: 'users', url: 'http://users' }, { name: 'products', url: 'http://products' }] }) -> Option C

4. Quick Check:

   ApolloGateway needs services array with name and url [OK]

Hint: Use services array with name and url objects in ApolloGateway [OK]

Common Mistakes:

• Passing services as simple string array
• Using 'endpoints' instead of 'services'
• Omitting 'new' keyword

3. Given this ApolloGateway setup:

const gateway = new ApolloGateway({
  services: [
    { name: 'users', url: 'http://localhost:4001/graphql' },
    { name: 'products', url: 'http://localhost:4002/graphql' }
  ],
  __exposeQueryPlanExperimental: false
});

What will be the result if a client queries for a product's name and its owner's username?

medium

A. The gateway throws an error because __exposeQueryPlanExperimental is false

B. The gateway returns data only from 'products' service ignoring 'users'

C. The gateway returns empty data because services are unreachable

D. The gateway fetches data from both 'products' and 'users' services and returns combined result

Solution

1. Step 1: Understand gateway data fetching

   The gateway composes schemas and fetches data from all relevant services for the query.

2. Step 2: Analyze the query involving product and user data

   Since the query asks for product and owner username, gateway calls both 'products' and 'users' services.

3. Final Answer:

   The gateway fetches data from both 'products' and 'users' services and returns combined result -> Option D

4. Quick Check:

   Gateway combines data from multiple services [OK]

Hint: Gateway merges data from all services needed by query [OK]

Common Mistakes:

• Assuming gateway fetches from only one service
• Confusing __exposeQueryPlanExperimental with data fetching
• Assuming error without service failure

4. You wrote this ApolloGateway code but get an error:

const gateway = new ApolloGateway({
  services: [
    { name: 'users', url: 'http://localhost:4001/graphql' },
    { name: 'products' }
  ]
});

What is the likely cause of the error?

medium

A. Missing 'url' property for the 'products' service

B. Using 'services' instead of 'endpoints'

C. ApolloGateway requires only one service

D. The 'name' property should be 'serviceName'

Solution

1. Step 1: Check service definitions

   Each service object must have both 'name' and 'url' properties.

2. Step 2: Identify missing property

   The 'products' service lacks the 'url' property, causing the error.

3. Final Answer:

   Missing 'url' property for the 'products' service -> Option A

4. Quick Check:

   Each service needs name and url [OK]

Hint: Always include 'url' for each service in ApolloGateway [OK]

Common Mistakes:

• Confusing 'services' with 'endpoints'
• Thinking ApolloGateway supports single service only
• Using wrong property names

5. You want to disable subscriptions in your ApolloGateway setup while composing three services. Which is the correct way to do this?

hard

A. Set subscriptions: false inside each service definition in ApolloGateway

B. Pass { subscriptions: false } in ApolloServer constructor, not in ApolloGateway

C. Add subscriptions: false in ApolloGateway constructor options

D. Disable subscriptions by removing the 'subscriptions' field from the schema

Solution

1. Step 1: Understand where to disable subscriptions

   Subscriptions are disabled in ApolloServer, not ApolloGateway.

2. Step 2: Apply correct configuration

   Pass { subscriptions: false } as an option to ApolloServer constructor wrapping the gateway.

3. Final Answer:

   Pass { subscriptions: false } in ApolloServer constructor, not in ApolloGateway -> Option B

4. Quick Check:

   Disable subscriptions in ApolloServer, not ApolloGateway [OK]

Hint: Disable subscriptions in ApolloServer, not ApolloGateway [OK]

Common Mistakes:

• Trying to disable subscriptions inside ApolloGateway
• Removing schema fields instead of config
• Setting subscriptions false per service