cdk-appsync-data-source-sfn-express

A CDK construct to create an AWS AppSync data source to call AWS Step Functions express workflows.

What is this?

This construct provides an HTTP data source for AWS AppSync that uses IAM authentication and calls AWS Step Functions API - StartSyncExecution. This is a stop-gap solution until AWS provides a native integration with this API like they have for AWS Lambda or Amazon DynamoDB.

Then, the construct can easily create a resolver to call this API, which means you can build AppSync GraphQL API by running a Step Functions state machine synchronously just like Amazon API Gateway already has, too.

Also, this is a showcase for how to use HTTP data source for non-RESTful AWS endpoints.

Usage

declare const api: appsync.CfnGraphQLApi;
declare const stateMachine: stepfunctions.StateMachine;

const schema = new appsync.CfnGraphQLSchema(stack, 'Schema', {
  apiId: api.attrApiId,
  definition: `
    type Query {
      getPost(id: Int): Post
    }
    type Post {
      id: Int
      title: String
    }
  `,
});

const sfnExpressDataSource = new AppSyncDataSourceStepFunctionsExpress(stack, 'SfnExpressDataSource', {
  apiId: api.attrApiId,
});

sfnExpressDataSource.createStateMachineResolver('Resolver', {
  stateMachine,
  schema,
  typeName: 'Query',
  fieldName: 'getPost',
});

When queried, the specified state machine receives input as the arguments of getPost() e.g.:

query MyQuery {
  getPost(id: 1)
}

is transformed to:

{
  "id": 1
}

And the state machine should return the output like below:

{
  "id": 1,
  "title": "Hello world!"
}

Then, AppSync returns the output as the return type of the query:

{
  "data": {
    "getPost": {
      "id": 1,
      "title": "Hello world!"
    }
  }
}

Notes

• The state machine must be EXPRESS type. See Step Functions document for more details.
• Currently, this construct doesn't have a good error handling on the response mapping.
  • We need to handle the case when the workflow fails because StartSyncExecution returns 200. See Step Functions document.

Authors

OpsBR Software Technology Inc. Visit our website: https://opsbr.com

License

Apache 2.0