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

Requires

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

optiondefaultdescription
apiKey0123456789When using API_KEY as authentication type, the key to authenticate to the endpoint.
port20002AppSync operations port; if using multiple APIs, the value of this option will be used as a starting point, and each other API will have a port of lastPort + 10 (e.g. 20002, 20012, 20022, etc.)
wsPort20003AppSync subscriptions port; if using multiple APIs, the value of this option will be used as a starting point, and each other API will have a port of lastPort + 10 (e.g. 20003, 20013, 20023, etc.)
location. (base directory)Location of the lambda functions handlers.
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.endpointhttp://localhost:8000Dynamodb endpoint. Specify it if you're not using serverless-dynamodb-local. Otherwise, port is taken from dynamodb-local conf
dynamoDb.regionlocalhostDynamodb region. Specify it if you're connecting to a remote Dynamodb intance.
dynamoDb.accessKeyIdDEFAULT_ACCESS_KEYAWS Access Key ID to access DynamoDB
dynamoDb.secretAccessKeyDEFAULT_SECRETAWS Secret Key to access DynamoDB
dynamoDb.sessionTokenDEFAULT_ACCESS_TOKEENAWS 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
rds.dbNameName of the database
rds.dbHostDatabase host
rds.dbDialectDatabase dialect. Possible values (mysql/postgres)
rds.dbUsernameDatabase username
rds.dbPasswordDatabase password
rds.dbPortDatabase port
openSearch.useSignaturefalseEnable signing requests to OpenSearch. The preference for credentials is config > environment variables > local credential file.
openSearch.regionOpenSearch region. Specify it if you're connecting to a remote OpenSearch intance.
openSearch.accessKeyIdAWS Access Key ID to access OpenSearch
openSearch.secretAccessKeyAWS Secret Key to access OpenSearch
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, which is then passed to watchman as the match expression.

e.g.

custom:
appsync-simulator:
watch:
- ["match", "handlers/**/*.vtl", "wholename"] # => array is interpreted as the literal match expression
- "*.graphql" # => string like this is equivalent to `["match", "*.graphql"]`

Or you can opt-out by leaving an empty 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'

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_ELASTICSEARCH
  • HTTP
  • RELATIONAL_DATABASE

Relational Database

Sample VTL for a create mutation

#set( $cols = [] )
#set( $vals = [] )
#foreach( $entry in $ctx.args.input.keySet() )
#set( $regex = "([a-z])([A-Z]+)")
#set( $replacement = "$1_$2")
#set( $toSnake = $entry.replaceAll($regex, $replacement).toLowerCase() )
#set( $discard = $cols.add("$toSnake") )
#if( $util.isBoolean($ctx.args.input[$entry]) )
#if( $ctx.args.input[$entry] )
#set( $discard = $vals.add("1") )
#else
#set( $discard = $vals.add("0") )
#end
#else
#set( $discard = $vals.add("'$ctx.args.input[$entry]'") )
#end
#end
#set( $valStr = $vals.toString().replace("[","(").replace("]",")") )
#set( $colStr = $cols.toString().replace("[","(").replace("]",")") )
#if ( $valStr.substring(0, 1) != '(' )
#set( $valStr = "($valStr)" )
#end
#if ( $colStr.substring(0, 1) != '(' )
#set( $colStr = "($colStr)" )
#end
{
"version": "2018-05-29",
"statements": ["INSERT INTO <name-of-table> $colStr VALUES $valStr", "SELECT * FROM <name-of-table> ORDER BY id DESC LIMIT 1"]
}

Sample VTL for an update mutation

#set( $update = "" )
#set( $equals = "=" )
#foreach( $entry in $ctx.args.input.keySet() )
#set( $cur = $ctx.args.input[$entry] )
#set( $regex = "([a-z])([A-Z]+)")
#set( $replacement = "$1_$2")
#set( $toSnake = $entry.replaceAll($regex, $replacement).toLowerCase() )
#if( $util.isBoolean($cur) )
#if( $cur )
#set ( $cur = "1" )
#else
#set ( $cur = "0" )
#end
#end
#if ( $util.isNullOrEmpty($update) )
#set($update = "$toSnake$equals'$cur'" )
#else
#set($update = "$update,$toSnake$equals'$cur'" )
#end
#end
{
"version": "2018-05-29",
"statements": ["UPDATE <name-of-table> SET $update WHERE id=$ctx.args.input.id", "SELECT * FROM <name-of-table> WHERE id=$ctx.args.input.id"]
}

Sample resolver for delete mutation

{
"version": "2018-05-29",
"statements": ["UPDATE <name-of-table> set deleted_at=NOW() WHERE id=$ctx.args.id", "SELECT * FROM <name-of-table> WHERE id=$ctx.args.id"]
}

Sample mutation response VTL with support for handling AWSDateTime

#set ( $index = -1)
#set ( $result = $util.parseJson($ctx.result) )
#set ( $meta = $result.sqlStatementResults[1].columnMetadata)
#foreach ($column in $meta)
#set ($index = $index + 1)
#if ( $column["typeName"] == "timestamptz" )
#set ($time = $result["sqlStatementResults"][1]["records"][0][$index]["stringValue"] )
#set ( $nowEpochMillis = $util.time.parseFormattedToEpochMilliSeconds("$time.substring(0,19)+0000", "yyyy-MM-dd HH:mm:ssZ") )
#set ( $isoDateTime = $util.time.epochMilliSecondsToISO8601($nowEpochMillis) )
$util.qr( $result["sqlStatementResults"][1]["records"][0][$index].put("stringValue", "$isoDateTime") )
#end
#end
#set ( $res = $util.parseJson($util.rds.toJsonString($util.toJson($result)))[1][0] )
#set ( $response = {} )
#foreach($mapKey in $res.keySet())
#set ( $s = $mapKey.split("_") )
#set ( $camelCase="" )
#set ( $isFirst=true )
#foreach($entry in $s)
#if ( $isFirst )
#set ( $first = $entry.substring(0,1) )
#else
#set ( $first = $entry.substring(0,1).toUpperCase() )
#end
#set ( $isFirst=false )
#set ( $stringLength = $entry.length() )
#set ( $remaining = $entry.substring(1, $stringLength) )
#set ( $camelCase = "$camelCase$first$remaining" )
#end
$util.qr( $response.put("$camelCase", $res[$mapKey]) )
#end
$utils.toJson($response)

Using Variable Map

Variable map support is limited and does not differentiate numbers and strings data types, please inject them directly if needed.

Will be escaped properly: null, true, and false values.

{
"version": "2018-05-29",
"statements": [
"UPDATE <name-of-table> set deleted_at=NOW() WHERE id=:ID",
"SELECT * FROM <name-of-table> WHERE id=:ID and unix_timestamp > $ctx.args.newerThan"
],
variableMap: {
":ID": $ctx.args.id,
## ":TIMESTAMP": $ctx.args.newerThan -- This will be handled as a string!!!
}
}

Contributors โœจ

Thanks goes to these wonderful people (emoji key):

This project follows the all-contributors specification. Contributions of any kind welcome!