This serverless plugin is a wrapper for amplify-appsync-simulator made for testing AppSync APIs built with serverless-appsync-plugin.

• serverless framework
• serverless-appsync-plugin
• serverless-offline
• serverless-dynamodb-local (when using dynamodb resolvers only)

npm install serverless-appsync-simulator
# or
yarn add serverless-appsync-simulator

This plugin relies on your serverless yml file and on the serverless-offline plugin.

plugins:
  - serverless-dynamodb-local # only if you need dynamodb resolvers and you don't have an external dynamodb
  - serverless-appsync-simulator
  - serverless-offline

Note: Order is important serverless-appsync-simulator must go before serverless-offline

To start the simulator, run the following command:

sls offline start

You should see in the logs something like:

...
Serverless: AppSync endpoint: http://localhost:20002/graphql
Serverless: GraphiQl: http://localhost:20002
...

Put options under custom.appsync-simulator in your serverless.yml file

Example:

custom:
  appsync-simulator:
    location: '.webpack/service' # use webpack build directory
    dynamoDb:
      endpoint: 'http://my-custom-dynamo:8000'

This plugin supports some resources resolution from the Ref and Fn::GetAtt functions in your yaml file. It also supports some other Cfn functions such as Fn::Join, Fb::Sub, etc.

Note: Under the hood, this features relies on the cfn-resolver-lib package. For more info on supported cfn functions, refer to the documentation

You can reference resources in your functions' environment variables (that will be accessible from your lambda functions) or datasource definitions. The plugin will automatically resolve them for you.

provider:
  environment:
    BUCKET_NAME:
      Ref: MyBucket # resolves to `my-bucket-name`

resources:
  Resources:
    MyDbTable:
      Type: AWS::DynamoDB::Table
      Properties:
        TableName: myTable
      ...
    MyBucket:
      Type: AWS::S3::Bucket
      Properties:
        BucketName: my-bucket-name
    ...

# in your appsync config
dataSources:
  - type: AMAZON_DYNAMODB
    name: dynamosource
    config:
      tableName:
        Ref: MyDbTable # resolves to `myTable`

Sometimes, some references cannot be resolved, as they come from an Output from Cloudformation; or you might want to use mocked values in your local environment.

In those cases, you can define (or override) those values using the refMap and getAttMap options.

• refMap takes a mapping of resource name to value pairs
• getAttMap takes a mapping of resource name to attribute/values pairs

Example:

custom:
  serverless-appsync-simulator:
    refMap:
      # Override `MyDbTable` resolution from the previous example.
      MyDbTable: 'mock-myTable'
    getAttMap:
      # define ElasticSearchInstance DomainName
      ElasticSearchInstance:
        DomainEndpoint: "localhost:9200"

# in your appsync config
dataSources:
  - type: AMAZON_ELASTICSEARCH
    name: elasticsource
    config:
      # endpoint resolves as 'http://localhost:9200'
      endpoint:
        Fn::Join:
          - ""
          - - https://
            - Fn::GetAtt:
                - ElasticSearchInstance
                - DomainEndpoint

This plugin only tries to resolve the following parts of the yml tree:

• provider.environment
• functions[*].environment
• custom.appSync

If you have the need of resolving others, feel free to open an issue and explain your use case.

For now, the supported resources to be automatically resovled by Ref: are:

• DynamoDb tables
• S3 Buckets

Feel free to open a PR or an issue to extend them as well.

This plugin supports resolvers implemented by amplify-appsync-simulator, as well as custom resolvers.

From Aws Amplify:

• NONE
• AWS_LAMBDA (*)
• AMAZON_DYNAMODB
• PIPELINE

Implemented by this plugin

• AWS_LAMBDA (*)
• AMAZON_ELASTIC_SEARCH
• HTTP

(*) The AWS_LAMBDA dataloader has been partially copied from Aws Amplify but has been extended to support the BatchInvoke operations

Not Supported / TODO

• RELATIONAL_DATABASE