how to loop through json input - aws step function / state machine - json

Question

Is it possible to create a loop in aws step function and loop through json input array?
I have a function generateEmails that creates array with n number of objects:
{
"emails": [
{
"to": [
"willow1#aaa.co.uk"
]
},
{
"to": [
"willow2#aaa.co.uk"
]
}, {
"to": [
"willow3#aaa.co.uk"
]
}
]
}
and now I want to call next function sendEmail for each object in emails array with something like this:
{
"email": {
"to": [
"willow#aaa.co.uk"
]
}
}
step function code:
{
"Comment": "A state machine that prepares and sends confirmation email ",
"StartAt": "generateEmails",
"States": {
"generateEmails": {
"Type": "Task",
"Resource": "arn:aws:lambda::prepare-confirmation-email",
"Next": "sendEmail"
},
"sendEmail": {
"Type": "Task",
"Resource": "arn:aws:lambda::function:template-service",
"End" : true
}
}
}
Is that possible to achieve?
Thanks!

Answer 1

Yes, the Step Functions Map state makes this easy.
https://docs.aws.amazon.com/step-functions/latest/dg/amazon-states-language-map-state.html
Map allows you to run the same set of operations to each item in an array. If you set the MaxConcurrency field to something larger than 1, then it will do these in parallel. Or you can set to 1 and it will iterate through sequentially.
For the scenario you described, the number of items will probably mean that "Inline" Map will work just fine. But if that list is larger and you want to fan out to higher concurrency, the recently launched Distributed Map feature will let you do so.
https://aws.amazon.com/blogs/aws/step-functions-distributed-map-a-serverless-solution-for-large-scale-parallel-data-processing/