(appsync): Fails with error "Only one resolver is allowed per field." in using 1.91.0

❓ General Issue

The Question

After upgrading to 1.91.0 from 1.90.1 my AppSync API is failing with the error:

Only one resolver is allowed per field. (Service: AWSAppSync; Status Code: 400; Error Code: BadRequestException; Request ID: ea61d8d6-1d06-4009-8054-8a2493ceb42b; Proxy: null)

My API has a mix of templated resolvers and a Lambda, none are duplicated as far as I can tell. Here is the relevant code:

const api = new appsync.GraphqlApi(this, "API", {
  name: "dataset-requests",
  schema: appsync.Schema.fromAsset("graphql/schema.graphql"),
  authorizationConfig: {
    defaultAuthorization: {
      authorizationType: appsync.AuthorizationType.API_KEY,
      apiKeyConfig: {
        expires: cdk.Expiration.after(cdk.Duration.days(365)),
      },
    },
  },
  xrayEnabled: true,
});

const dataSource = api.addDynamoDbDataSource("dataSource", table);

dataSource.createResolver({
  typeName: "Query",
  fieldName: "getDatasetRequests",
  requestMappingTemplate: appsync.MappingTemplate.dynamoDbScanTable(),
  responseMappingTemplate: appsync.MappingTemplate.dynamoDbResultList(),
});

dataSource.createResolver({
  typeName: "Mutation",
  fieldName: "createDatasetRequest",
  requestMappingTemplate: appsync.MappingTemplate.fromFile(
    "lib/appsync/templates/Mutation.createDatasetRequest.req.vtl",
  ),
  responseMappingTemplate: appsync.MappingTemplate.dynamoDbResultItem(),
});

dataSource.createResolver({
  typeName: "Query",
  fieldName: "getDatasetRequestById",
  requestMappingTemplate: appsync.MappingTemplate.dynamoDbGetItem("id", "id"),
  responseMappingTemplate: appsync.MappingTemplate.dynamoDbResultItem(),
});

const graphqlLamda = new lambdaNodeJS.NodejsFunction(this, "GraphQLLambda", {
  entry: "../lambda-graphql/src/graphql/index.ts",
  handler: "handler",
  runtime: lambda.Runtime.NODEJS_14_X,
  environment: {
    TABLE_NAME: table.tableName,
  },
});
table.grantFullAccess(graphqlLamda);

// Set the new Lambda function as a data source for the AppSync API
const lambdaDs = api.addLambdaDataSource("lambdaDatasource", graphqlLamda);

lambdaDs.createResolver({
  typeName: "Mutation",
  fieldName: "approveDatasetRequest",
});

lambdaDs.createResolver({
  typeName: "Mutation",
  fieldName: "rejectDatasetRequest",
});

–

Environment

• CDK CLI Version: 1.91.0
• Module Version: @aws-cdk/aws-appsync 1.91.0
• Node.js Version: v14.15.1
• OS: macOS Big Sur
• Language (Version): TypeScript 4.2

Other information

[bigkraig]

Parallel instances won’t work if you use API keys, as you cannot specify the key value when creating them.

[simiyu1]

I had this issue for the last 2 days… My structure is several microservices expose their schemas to AppSync which then compiles them to gether with their resolvers into one. My bug was caused by one microservice that was trying to create the resolver’s datasource. The fix was to ensure that no microservices is trying to create the datasources. Create is only done by Appsync API…

Might be worth looking into if you are also facing this.