AWS StateMachine for Lambda, cloud formation syntax - amazon-web-services

Question

I'm trying to come up with a CloudFormation template that includes
API Gateway
Invokes a StateMachine through the API Gateway
StateMachine in turn contains a lambda function
In essence what I'm try to do is the following
https://docs.aws.amazon.com/step-functions/latest/dg/tutorial-api-gateway.html
However I'm stuck in coming up with the Cloud Formation Template (.yaml) that will deploy this. So far this is what I have
AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Resources:
Post:
Type: AWS::Serverless::Function
Properties:
FunctionName: UserBase-fnUsers
Handler: UsersHandler.getUsers
Runtime: nodejs6.10
Policies: [AmazonDynamoDBReadOnlyAccess, AmazonS3ReadOnlyAccess]
Environment:
Variables:
S3_BUCKET: UserBase-Users-bucket
UsersTable: UserBase-Users-tblUsers
Events:
GetUsers:
Type: Api
Properties:
Path: /UserBase/Users
Method: post
Options:
Type: AWS::Serverless::Function
Properties:
FunctionName: UserBase-fnUsers-Options
Handler: UsersHandler.getOptions
Runtime: nodejs6.10
Events:
GetOptions:
Type: Api
Properties:
Path: /UserBase/Users
Method: options
UsersTable:
Type: AWS::DynamoDB::Table
Properties:
TableName: UserBase-Users-tblUsers
AttributeDefinitions:
- AttributeName: Id
AttributeType: S
KeySchema:
- AttributeName: Id
KeyType: HASH
ProvisionedThroughput:
ReadCapacityUnits: 5
WriteCapacityUnits: 5
StreamSpecification:
StreamViewType: KEYS_ONLY
StatesExecutionRole:
Type: "AWS::IAM::Role"
Properties:
AssumeRolePolicyDocument:
Version: "2012-10-17"
Statement:
- Effect: "Allow"
Principal:
Service:
- !Sub states.${AWS::Region}.amazonaws.com
Action: "sts:AssumeRole"
Path: "/"
Policies:
- PolicyName: StatesExecutionPolicy
PolicyDocument:
Version: "2012-10-17"
Statement:
- Effect: Allow
Action:
- "lambda:InvokeFunction"
Resource: "*"
UpdateShoppingPath:
Type: "AWS::StepFunctions::StateMachine"
Properties:
DefinitionString:
!Sub
- |-
{
"Comment": "State machine to update the shopping path",
"StartAt": "UpdatePath",
"States": {
"UpdatePath": {
"Type": "Task",
"Resource": "${lambdaArn}",
"End": true
}
}
}
- {lambdaArn: !GetAtt [ Post, Arn ]}
RoleArn: !GetAtt [ StatesExecutionRole, Arn ]
UserBaseUsers:
Type: "AWS::ApiGateway::Resource"
I'm stuck with the last piece, basically on how to link the ApiGateway to the StateMachine. On a side note is there any way for me to generate the cloud formation template (.yaml or json) from an existing deployment in AWS?

Answer 1

I'm not an expert with yaml, but I did some configuration with json CloudFormation and as far as I have read it's quite easy to translate.
In the past I've been stuck like you, and here's my post and my solution
What you need to do to start the execution of a Step Functions is to do a HTTP Post to arn:aws:apigateway:${region}:states:action/StartExecution passing as json object [docs]:
{
input: __input__,
stateMachineArn: __arn__
}
In short, in your AWS::ApiGateway::Method, you have to set an HTTP integration to arn:aws:apigateway:${region}:states:action/StartExecution and a requestTemplate that builds the json object I mentioned.
For reference, here my json cloudformation example:
"FooRequest": {
"DependsOn": ["FooStepMachine"],
"Type": "AWS::ApiGateway::Method",
"Properties": {
"HttpMethod": "POST",
"Integration": {
"Type": "AWS",
"Credentials": {
"Fn::GetAtt": ["FooRole",
"Arn"]
},
"IntegrationHttpMethod": "POST",
"Uri": {
"Fn::Join": ["",
["arn:aws:apigateway:",
{
"Ref": "AWS::Region"
},
":states:action/StartExecution"]]
},
"IntegrationResponses": [{
"StatusCode": 200
},
{
"StatusCode": 401
}],
"RequestTemplates": {
"application/json": {
"Fn::Sub": ["{\"input\": \"$util.escapeJavaScript($input.json('$'))\",\"stateMachineArn\": \"${arn}\"}",
{
"arn": {
"Ref": "FooStepMachine"
}
}]
}
}
}
}
}