Tutorial: HTTP resolvers - Amazon AppSync
Creating a REST APICreating your GraphQL APICreating a GraphQL schemaConfigure your HTTP data sourceConfiguring resolversInvoking Amazon Services
Services or capabilities described in Amazon Web Services documentation might vary by Region. To see the differences applicable to the China Regions, see Getting Started with Amazon Web Services in China (PDF).

Tutorial: HTTP resolvers

Amazon AppSync enables you to use supported data sources (that is, Amazon Lambda, Amazon DynamoDB, Amazon OpenSearch Service, or Amazon Aurora) to perform various operations, in addition to any arbitrary HTTP endpoints to resolve GraphQL fields. After your HTTP endpoints are available, you can connect to them using a data source. Then, you can configure a resolver in the schema to perform GraphQL operations such as queries, mutations, and subscriptions. This tutorial walks you through some common examples.

In this tutorial you use a REST API (created using Amazon API Gateway and Lambda) with an Amazon AppSync GraphQL endpoint.

Creating a REST API

You can use the following Amazon CloudFormation template to set up a REST endpoint that works for this tutorial:

The Amazon CloudFormation stack performs the following steps:

  1. Sets up a Lambda function that contains your business logic for your microservice.

  2. Sets up an API Gateway REST API with the following endpoint/method/content type combination:

API Resource Path HTTP Method Supported Content Type

/v1/users

POST

application/json

/v1/users

GET

application/json

/v1/users/1

GET

application/json

/v1/users/1

PUT

application/json

/v1/users/1

DELETE

application/json

Creating your GraphQL API

To create the GraphQL API in Amazon AppSync:

  1. Open the Amazon AppSync console and choose Create API.

  2. Choose GraphQL APIs and then choose Design from scratch. Choose Next.

  3. For the API name, type UserData. Choose Next.

  4. Choose Create GraphQL resources later. Choose Next.

  5. Review your inputs and choose Create API.

The Amazon AppSync console creates a new GraphQL API for you using the API key authentication mode. You can use the console to further configure your GraphQL API and run requests.

Creating a GraphQL schema

Now that you have a GraphQL API, let’s create a GraphQL schema. In the Schema editor in the Amazon AppSync console, use the snippet below:

type Mutation {
    addUser(userInput: UserInput!): User
    deleteUser(id: ID!): User
}

type Query {
    getUser(id: ID): User
    listUser: [User!]!
}

type User {
    id: ID!
    username: String!
    firstname: String
    lastname: String
    phone: String
    email: String
}

input UserInput {
    id: ID!
    username: String!
    firstname: String
    lastname: String
    phone: String
    email: String
}

Configure your HTTP data source

To configure your HTTP data source, do the following:

  1. In the Data sources page in your Amazon AppSync GraphQL API, choose Create data source.

  2. Enter a name for the data source like HTTP_Example.

  3. In Data source type, choose HTTP endpoint.

  4. Set the endpoint to the API Gateway endpoint that was created at the beginning of the tutorial. You can find your stack-generated endpoint if you navigate to the Lambda console and find your application under Applications. Inside of your application's settings, you should see an API endpoint which will be your endpoint in Amazon AppSync. Make sure you don’t include the stage name as part of the endpoint. For instance, if your endpoint were https://aaabbbcccd.execute-api.us-east-1.amazonaws.com/v1, you would type in https://aaabbbcccd.execute-api.us-east-1.amazonaws.com.

Note

At this time, only public endpoints are supported by Amazon AppSync.

For more information about the certifying authorities that are recognized by the Amazon AppSync service, see Certificate Authorities (CA) Recognized by Amazon AppSync for HTTPS Endpoints.

Configuring resolvers

In this step, you will connect the HTTP data source to the getUser and addUser queries.

To set up the getUser resolver:

  1. In your Amazon AppSync GraphQL API, choose the Schema tab.

  2. To the right of the Schema editor, in the Resolvers pane and under the Query type, find the getUser field and choose Attach.

  3. Keep the resolver type to Unit and the runtime to APPSYNC_JS.

  4. In Data source name, choose the HTTP endpoint you made earlier.

  5. Choose Create.

  6. In the Resolver code editor, add the following snippet as your request handler:

    import { util } from '@aws-appsync/utils'

export function request(ctx) {
	return {
		version: '2018-05-29',
		method: 'GET',
		params: {
			headers: {
				'Content-Type': 'application/json',
			},
		},
		resourcePath: `/v1/users/${ctx.args.id}`,
	}
}

  7. Add the following snippet as your response handler:

    export function response(ctx) {
	const { statusCode, body } = ctx.result
	// if response is 200, return the response
	if (statusCode === 200) {
		return JSON.parse(body)
	}
	// if response is not 200, append the response to error block.
	util.appendError(body, statusCode)
}

  8. Choose the Query tab, and then run the following query:

    query GetUser{
    getUser(id:1){
        id
        username
    }
}

    This should return the following response:

    {
    "data": {
        "getUser": {
            "id": "1",
            "username": "nadia"
        }
    }
}

To set up the addUser resolver:

  1. Choose the Schema tab.

  2. To the right of the Schema editor, in the Resolvers pane and under the Query type, find the addUser field and choose Attach.

  3. Keep the resolver type to Unit and the runtime to APPSYNC_JS.

  4. In Data source name, choose the HTTP endpoint you made earlier.

  5. Choose Create.

  6. In the Resolver code editor, add the following snippet as your request handler:

    export function request(ctx) {
    return {
        "version": "2018-05-29",
        "method": "POST",
        "resourcePath": "/v1/users",
        "params":{
            "headers":{
                "Content-Type": "application/json"
            },
        "body": ctx.args.userInput
        }
    }
}

  7. Add the following snippet as your response handler:

    export function response(ctx) {
    if(ctx.error) {
        return util.error(ctx.error.message, ctx.error.type)
    }
    if (ctx.result.statusCode == 200) {
        return ctx.result.body
    } else {
        return util.appendError(ctx.result.body, "ctx.result.statusCode")
    }
}

  8. Choose the Query tab, and then run the following query:

    mutation addUser{
    addUser(userInput:{
        id:"2",
        username:"shaggy"
    }){
        id
        username
    }
}

    If you run the getUser query again, it should return the following response:

    {
    "data": {
        "getUser": {
        "id": "2",
        "username": "shaggy"
        }
    }
}

Invoking Amazon Services

You can use HTTP resolvers to set up a GraphQL API interface for Amazon services. HTTP requests to Amazon must be signed with the Signature Version 4 process so that Amazon can identify who sent them. Amazon AppSync calculates the signature on your behalf when you associate an IAM role with the HTTP data source.

You provide two additional components to invoke Amazon services with HTTP resolvers:

  • An IAM role with permissions to call the Amazon service APIs

  • Signing configuration in the data source

For example, if you want to call the ListGraphqlApis operation with HTTP resolvers, you first create an IAM role that Amazon AppSync assumes with the following policy attached:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Action": [
                "appsync:ListGraphqlApis"
            ],
            "Effect": "Allow",
            "Resource": "*"
        }
    ]
}

Next, create the HTTP data source for Amazon AppSync. In this example, you call Amazon AppSync in the US West (Oregon) Region. Set up the following HTTP configuration in a file named http.json, which includes the signing region and service name:

{
    "endpoint": "https://appsync.us-west-2.amazonaws.com/",
    "authorizationConfig": {
        "authorizationType": "AWS_IAM",
        "awsIamConfig": {
            "signingRegion": "us-west-2",
            "signingServiceName": "appsync"
        }
    }
}

Then, use the Amazon CLI to create the data source with an associated role as follows:

aws appsync create-data-source --api-id <API-ID> \
                               --name AWSAppSync \
                               --type HTTP \
                               --http-config file:///http.json \
                               --service-role-arn <ROLE-ARN>

When you attach a resolver to the field in the schema, use the following request mapping template to call Amazon AppSync:

{
    "version": "2018-05-29",
    "method": "GET",
    "resourcePath": "/v1/apis"
}

When you run a GraphQL query for this data source, Amazon AppSync signs the request using the role you provided and includes the signature in the request. The query returns a list of Amazon AppSync GraphQL APIs in your account in that Amazon Region.