Direct Lambda resolvers (VTL) - Amazon AppSync
Configure direct Lambda resolvers
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Direct Lambda resolvers (VTL)

Note

We now primarily support the APPSYNC_JS runtime and its documentation. Please consider using the APPSYNC_JS runtime and its guides here.

With direct Lambda resolvers, you can circumvent the use of VTL mapping templates when using Amazon Lambda data sources. Amazon AppSync can provide a default payload to your Lambda function as well as a default translation from a Lambda function's response to a GraphQL type. You can choose to provide a request template, a response template, or neither and Amazon AppSync will handle it accordingly.

To learn more about the default request payload and response translation that Amazon AppSync provides, see the Direct Lambda resolver reference. For more information on setting up an Amazon Lambda data source and setting up an IAM Trust Policy, see Attaching a data source.

Configure direct Lambda resolvers

The following sections will show you how to attach Lambda data sources and add Lambda resolvers to your fields.

Add a Lambda data source

Before you can activate direct Lambda resolvers, you must add a Lambda data source.

Console

  1. Sign in to the Amazon Web Services Management Console and open the AppSync console.

    1. In the APIs dashboard, choose your GraphQL API.

    2. In the Sidebar, choose Data sources.

  2. Choose Create data source.

    1. For Data source name, enter a name for your data source, such as myFunction.

    2. For Data source type, choose Amazon Lambda function.

    3. For Region, choose the appropriate region.

    4. For Function ARN, choose the Lambda function from the dropdown list. You can search for the function name or manually enter the ARN of the function you want to use.

    5. Create a new IAM role (recommended) or choose an existing role that has the lambda:invokeFunction IAM permission. Existing roles need a trust policy, as explained in the Attaching a data source section.

      The following is an example IAM policy that has the required permissions to perform operations on the resource:

      { 
     "Version": "2012-10-17", 
     "Statement": [ 
         { 
             "Effect": "Allow", 
             "Action": [ "lambda:invokeFunction" ], 
             "Resource": [ 
                 "arn:aws:lambda:us-west-2:123456789012:function:myFunction", 
                 "arn:aws:lambda:us-west-2:123456789012:function:myFunction:*" 
             ] 
         } 
     ] 
 }

  3. Choose the Create button.

CLI

  1. Create a data source object by running the create-data-source command.

    You'll need to type in 4 parameters for this particular command:

    1. The api-id of your API.

    2. The name of your data source. In the console example, this is the Data source name.

    3. The type of data source. In the console example, this is Amazon Lambda function.

    4. The lambda-config, which is the Function ARN in the console example.

    Note

    There are other parameters such as Region that must be configured but will usually default to your CLI configuration values.

    An example command may look like this:

    aws appsync create-data-source --api-id abcdefghijklmnopqrstuvwxyz --name myFunction --type AWS_LAMBDA --lambda-config lambdaFunctionArn=arn:aws:lambda:us-west-2:102847592837:function:appsync-lambda-example

    An output will be returned in the CLI. Here's an example:

    {
    "dataSource": {
        "dataSourceArn": "arn:aws:appsync:us-west-2:102847592837:apis/abcdefghijklmnopqrstuvwxyz/datasources/myFunction",
        "type": "AWS_LAMBDA",
        "name": "myFunction",
        "lambdaConfig": {
            "lambdaFunctionArn": "arn:aws:lambda:us-west-2:102847592837:function:appsync-lambda-example"
        }
    }
}

  2. To modify a data source's attributes, run the update-data-source command.

    With the exception of the api-id parameter, the parameters used in the create-data-source command will be overwritten by the new values from the update-data-source command.

Activate direct Lambda resolvers

After creating a Lambda data source and setting up the appropriate IAM role to allow Amazon AppSync to invoke the function, you can link it to a resolver or pipeline function.

Console

  1. Sign in to the Amazon Web Services Management Console and open the AppSync console.

    1. In the APIs dashboard, choose your GraphQL API.

    2. In the Sidebar, choose Schema.

  2. In the Resolvers window, choose a field or operation and then select the Attach button.

  3. In the Create new resolver page, choose the Lambda function from the dropdown list.

  4. In order to leverage direct Lambda resolvers, confirm that request and response mapping templates are disabled in the Configure mapping templates section.

  5. Choose the Save Resolver button.

CLI

  • Create a resolver by running the create-resolver command.

    You'll need to type in 6 parameters for this particular command:

    1. The api-id of your API.

    2. The type-name of the type in your schema.

    3. The field-name of the field in your schema.

    4. The data-source-name, or your Lambda function's name.

    5. The request-mapping-template, which is the body of the request. In the console example, this was disabled:

      " "

    6. The response-mapping-template, which is the body of the response. In the console example, this was also disabled:

      " "

    An example command may look like this:

    aws appsync create-resolver --api-id abcdefghijklmnopqrstuvwxyz --type-name Subscription --field-name onCreateTodo --data-source-name LambdaTest --request-mapping-template " " --response-mapping-template " "

    An output will be returned in the CLI. Here's an example:

    {
    "resolver": {
        "resolverArn": "arn:aws:appsync:us-west-2:102847592837:apis/abcdefghijklmnopqrstuvwxyz/types/Subscription/resolvers/onCreateTodo",
        "typeName": "Subscription",
        "kind": "UNIT",
        "fieldName": "onCreateTodo",
        "dataSourceName": "LambdaTest"
    }
}

When you disable your mapping templates, there are several additional behaviors that will occur in Amazon AppSync:

  • By disabling a mapping template, you are signalling to Amazon AppSync that you accept the default data translations specified in the Direct Lambda resolver reference.

  • By disabling the request mapping template, your Lambda data source will receive a payload consisting of the entire Context object.

  • By disabling the response mapping template, the result of your Lambda invocation will be translated depending on the version of the request mapping template or if the request mapping template is also disabled.