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

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opsbr/cdk-appsync-data-source-sfn-express

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cdk-appsync-data-source-sfn-express

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

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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