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

Requires

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

Install

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

Usage

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
...

Configuration

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

option	default	description
apiKey	`0123456789`	When using `API_KEY` as authentication type, the key to authenticate to the endpoint.
port	20002	AppSync operations port
wsPort	20003	AppSync subscriptions port
location	. (base directory)	Location of the lambda functions handlers.
lambda.loadLocalEnv	false	If `true`, all environment variables (`$ env`) will be accessible from the resolver function. Read more in section Environment variables.
refMap	{}	A mapping of resource resolutions for the `Ref` function
getAttMap	{}	A mapping of resource resolutions for the `GetAtt` function
importValueMap	{}	A mapping of resource resolutions for the `ImportValue` function
functions	{}	A mapping of external functions for providing invoke url for external fucntions
dynamoDb.endpoint	http://localhost:8000	Dynamodb endpoint. Specify it if you're not using serverless-dynamodb-local. Otherwise, port is taken from dynamodb-local conf
dynamoDb.region	localhost	Dynamodb region. Specify it if you're connecting to a remote Dynamodb intance.
dynamoDb.accessKeyId	DEFAULT_ACCESS_KEY	AWS Access Key ID to access DynamoDB
dynamoDb.secretAccessKey	DEFAULT_SECRET	AWS Secret Key to access DynamoDB
dynamoDb.sessionToken	DEFAULT_ACCESS_TOKEEN	AWS Session Token to access DynamoDB, only if you have temporary security credentials configured on AWS
dynamoDb.*		You can add every configuration accepted by DynamoDB SDK
watch	- .graphql - .vtl	Array of glob patterns to watch for hot-reloading.

Example:

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

Hot-reloading

By default, the simulator will hot-relad when changes to *.graphql or *.vtl files are detected. Changes to *.yml files are not supported (yet? - this is a Serverless Framework limitation). You will need to restart the simulator each time you change yml files.

Hot-reloading relies on watchman. Make sure it is installed on your system.

You can change the files being watched with the watch option. Or you can opt-out by leaving an emptry array or set the option to false.

Note: Functions should not require hot-reloading, unless you are using a transpiler or a bundler (such as webpack, babel or typescript), un which case you should delegate hot-reloading to that instead.

Resource CloudFormation functions resolution

This plugin supports some resources resolution from the Ref, Fn::GetAtt and Fn::ImportValue 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

Basic usage

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`

Override (or mock) values

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, getAttMap and importValueMap options.

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

Example:

custom:
  appsync-simulator:
    refMap:
      # Override `MyDbTable` resolution from the previous example.
      MyDbTable: 'mock-myTable'
    getAttMap:
      # define ElasticSearchInstance DomainName
      ElasticSearchInstance:
        DomainEndpoint: 'localhost:9200'
    importValueMap:
      other-service-api-url: 'https://other.api.url.com/graphql'

# 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

Key-value mock notation

In some special cases you will need to use key-value mock nottation. Good example can be case when you need to include serverless stage value (${self:provider.stage}) in the import name.

This notation can be used with all mocks - refMap, getAttMap and importValueMap

provider:
  environment:
    FINISH_ACTIVITY_FUNCTION_ARN:
      Fn::ImportValue: other-service-api-${self:provider.stage}-url

custom:
  serverless-appsync-simulator:
    importValueMap:
      - key: other-service-api-${self:provider.stage}-url
        value: 'https://other.api.url.com/graphql'

Environment variables

custom:
  appsync-simulator:
    lambda:
      loadLocalEnv: true

If true, all environment variables ($ env) will be accessible from the resolver function.

If false, only environment variables defined in serverless.yml will be accessible from the resolver function.

Note: serverless.yml environment variables have higher priority than local environment variables. Thus some of your local environment variables, could get overridden by environment variables from serverless.yml.

Limitations

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.

External functions

When a function is not defined withing the current serverless file you can still call it by providing an invoke url which should point to a REST method. Make sure you specify "get" or "post" for the method. Default is "get", but you probably want "post".

custom:
  appsync-simulator:
    functions:
      addUser:
        url: http://localhost:3016/2015-03-31/functions/addUser/invocations
        method: post
      addPost:
        url: https://jsonplaceholder.typicode.com/posts
        method: post

Supported Resolver types

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

AMAZON_ELASTIC_SEARCH
HTTP

Not Supported / TODO

RELATIONAL_DATABASE

Contributors ✨

Thanks goes to these wonderful people (emoji key):

_{Benoît Bouré} 💻	_{Filip Pýrek} 💻	_{Marco Reni} 💻	_{Egor Dmitriev} 💻	_{Steffen Schwark} 💻	_{Nicky Moelholm} 💻	_g-awa 💻
_{Lee Mulvey} 💻	_{Jimmy Hurrah} 💻	_Abdala 🤔	_{Alexandru Savin} 📖	_Scale93 💻 📖