Using HTTP resolvers in AWS AppSync

AWS AppSync enables you to use supported data sources (that is, AWS 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 AWS AppSync GraphQL endpoint.

One-Click Setup

If you want to automatically set up a GraphQL endpoint in AWS AppSync with an HTTP endpoint configured (using Amazon API Gateway and Lambda), you can use the following AWS CloudFormation template :

Creating a REST API

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

The AWS CloudFormation stack performs the following steps:

Creating Your GraphQL API

To create the GraphQL API in AWS AppSync:

The AWS AppSync console creates a new GraphQL API for you using the API key authentication mode. You can use the console to set up the rest of the GraphQL API and run queries on it for the remainder of this tutorial.

Creating a GraphQL Schema

Now that you have a GraphQL API, let’s create a GraphQL schema. From the schema editor in the AWS AppSync console, make sure you schema matches the following schema:

schema {
    query: Query
    mutation: Mutation
}

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:

Note: At this time only public endpoints are supported by AWS AppSync.

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

Configuring Resolvers

In this step, you connect the http data source to the getUser query.

To set up the resolver:

{
    "version": "2018-05-29",
    "method": "GET",
    "params": {
        "headers": {
            "Content-Type": "application/json"
        }
    },
    "resourcePath": $util.toJson("/v1/users/${ctx.args.id}")
}

## return the body
#if($ctx.result.statusCode == 200)
    ##if response is 200
    $ctx.result.body
#else
    ##if response is not 200, append the response to error block.
    $utils.appendError($ctx.result.body, "$ctx.result.statusCode")
#end

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

This should return the following response:

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

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

## Raise a GraphQL field error in case of a datasource invocation error
#if($ctx.error)
    $util.error($ctx.error.message, $ctx.error.type)
#end
## if the response status code is not 200, then return an error. Else return the body **
#if($ctx.result.statusCode == 200)
    ## If response is 200, return the body.
    $ctx.result.body
#else
    ## If response is not 200, append the response to error block.
    $utils.appendError($ctx.result.body, "$ctx.result.statusCode")
#end

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

This should return the following response:

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

Invoking AWS Services

You can use HTTP resolvers to set up a GraphQL API interface for AWS services. HTTP requests to AWS must be signed with the Signature Version 4 process so that AWS can identify who sent them. AWS 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 AWS services with HTTP resolvers:

For example, if you want to call the ListGraphqlApis operation with HTTP resolvers, you first create an IAM role that AWS 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 AWS AppSync. In this example, you call AWS 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 AWS 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 AWS AppSync:

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

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