Gateway composition in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a basic gateway that composes two services.

GraphQL

const gateway = new ApolloGateway({ serviceList: [[1]] });

Drag options to blanks, or click blank then click option'

A{ name: 'users', url: 'http://localhost:4001/graphql' }, { name: 'products', url: 'http://localhost:4002/graphql' }

B'users'

C{ name: 'users', url: 'http://localhost:4001/graphql' }

D['users', 'products']

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a single object instead of an array.

Using just service names as strings without URLs.

The serviceList expects an array of service definitions with name and url keys.

2fill in blank

medium

Complete the code to start the Apollo Gateway server on port 4000.

GraphQL

gateway.listen({ port: [1] }).then(({ url }) => { console.log(`Gateway ready at ${url}`); });

Drag options to blanks, or click blank then click option'

A5000

B4000

C8080

D3000

Attempts:

3 left

💡 Hint

Common Mistakes

Using the port of one of the underlying services instead of the gateway port.

The gateway server is commonly started on port 4000 to avoid conflicts with underlying services.

3fill in blank

hard

Fix the error in the service list by completing the missing key.

GraphQL

const serviceList = [{ [1]: 'users', url: 'http://localhost:4001/graphql' }];

Drag options to blanks, or click blank then click option'

AserviceName

Bendpoint

Cname

Dtype

Attempts:

3 left

💡 Hint

Common Mistakes

Using endpoint or serviceName instead of name.

The key name is required to identify the service in the gateway's service list.

4fill in blank

hard

Fill both blanks to create a gateway that composes two services and logs the URL when ready.

GraphQL

const gateway = new ApolloGateway({ serviceList: [1] });
gateway.listen().then(({ [2] }) => console.log(`Gateway running at ${url}`));

Drag options to blanks, or click blank then click option'

A[{ name: 'accounts', url: 'http://localhost:4003/graphql' }, { name: 'reviews', url: 'http://localhost:4004/graphql' }]

Burl

Caddress

Dendpoint

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect property names like address or endpoint.

Passing a single service object instead of an array.

The serviceList must be an array of service objects, and the listen method returns an object with a url property.

5fill in blank

hard

Fill all three blanks to define a gateway with three services and start it on port 5000.

GraphQL

const gateway = new ApolloGateway({ serviceList: [1] });
gateway.listen({ port: [2] }).then(({ [3] }) => console.log(`Gateway ready at ${url}`));

Drag options to blanks, or click blank then click option'

A[{ name: 'users', url: 'http://localhost:4001/graphql' }, { name: 'products', url: 'http://localhost:4002/graphql' }, { name: 'orders', url: 'http://localhost:4005/graphql' }]

B5000

Curl

Dendpoint

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong port numbers or property names.

Not passing an array for the service list.

The serviceList is an array of three service objects, the gateway listens on port 5000, and the listen method returns an object with a url property.

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