Passing Input Parameters from one Step Function to another - amazon-web-services

Question

I do have an Step Function A - which executes a lambda and pull some results.
Same Function has a Map Stage which is iterating over results and should call another Step Function from Map State.
While calling another Step Function B from the map state i am not able to pass the parameter or that one record as Input to Step Function B.
Please suggest how can i use Input for second step function.
Below is the example i am using , orderServiceResponse has a List of orders which I need to iterate and pass that one order to next step function.
"Validate-All" : {
"Type" : "Map",
"InputPath" : "$.orderServiceResponse",
"ItemsPath" : "$.orders",
"MaxConcurrency" : 5,
"ResultPath" : "$.orders",
"Iterator" : {
"StartAt" : "Validate" ,
"States" :{
"Validate" : {
"Type" : "Task"
"Resource" : "arn:aws:states:::states:startExecution.sync:2",
"Parameters" {
"Input" : "$.orders",
"StateMachineArn" : "{arn of Step Function B }
},
"End" : true
}
}

Answer 1

TL;DR Use Parameters with Map Context to add the full input object to each Map element iteration.
You have an array of data you want to process elementwise in a Map State. By default, Map only passes
the array element's data to the map iterator. But we can add additional context to each iteration.
Here is an example - the important bits are commented:
{
"StartAt": "MapState",
"States": {
"MapState": {
"Type": "Map",
"ResultPath": "$.MapResult",
"Next": "Success",
// the map's elements of each get the following:
"Parameters": {
"Index.$": "$$.Map.Item.Index", // the array element's data (we only get this by default)
"Order.$": "$$.Map.Item.Value", // the array element's index 0,1,2...
"FullInput.$": "$" // a copy of the the full input object <-- this is what you were looking for
},
"Catch": [{ "ErrorEquals": ["States.ALL"], "Next": "Fail" }],
// substitute your iterator:
"Iterator": {
"StartAt": "MockTask",
"States": {
"MockTask": {
"End": true,
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:xxxxxxxxxxxx",
"Parameters": {
"expression": "`Order ${$.Order.OrderID} was ordered by ${$.FullInput.CustomerName}`",
"expressionAttributeValues": {
"$.Order.OrderID.$": "$.Order.OrderID",
"$.FullInput.CustomerName.$": "$.FullInput.CustomerName"
}
}
}
}
},
"ItemsPath": "$.Orders"
},
"Success": { "Type": "Succeed" },
"Fail": { "Type": "Fail" }
}
}
Execution Input, 3 Orders:
{
"CustomerID": 1,
"CustomerName": "Morgan Freeman",
"OtherInfo": { "Foo": "Bar" },
"Orders": [{ "OrderID": "A", "Status": "Fulfilled" }, { "OrderID": "B", "Status": "Pending" }, { "OrderID": "C", "Status": "Cancelled" }]
}
Map Iteration 0 Input:
{
"Order": { "OrderID": "A", "Status": "Fulfilled" },
"Index": 0,
"FullInput": { "CustomerID": 1, "CustomerName": "Morgan Freeman", "OtherInfo": { "Foo": "Bar" }, "Orders": [{...
Execution Output MapResult key
{
"MapResult": [
"Order A was ordered by Morgan Freeman",
"Order B was ordered by Morgan Freeman",
"Order C was ordered by Morgan Freeman"
]
...
}