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I am using AWS step function to iterate over a list in an input document where for each iteration, I need to invoke an external service. So I want to iterate over each item and run a step using lambda:invoke.waitForTaskToken and pass the TaskToken into the execution of each iteration.
The problem I'm running into is how to use both an ItemSelector at the Map state level but also inject the TaskToken during the internal step. I need to use an ItemSelector because I want each item to also contain information from the input to Map state. The AWS Docs state:
The ItemSelector field replaces the Parameters field within the Map state. If you use the Parameters field in your Map state definitions to create custom input, we highly recommend that you replace them with ItemSelector.
But they also say:
During an execution, the context object is populated with relevant data for the Parameters field from where it is accessed. The value for a Task field is null if the Parameters field is outside of a task state.
These two statements seem to imply that what I'm trying to do is impossible.
So, what I want is something like:
{
"StartAt": "ExampleMapState",
"States": {
"ExampleMapState": {
"Type": "Map",
"ItemsPath": "$.items",
"ItemSelector": {
"dynamic.$": "$.dynamic",
"ContextIndex.$": "$$.Map.Item.Index",
"ContextValue.$": "$$.Map.Item.Value"
},
"ItemProcessor": {
"ProcessorConfig": {
"Mode": "INLINE"
},
"StartAt": "TestPass",
"States": {
"TestPass": {
"Type": "Task",
"Parameters": {
"FunctionName": "arn:aws:lambda:us-west-2:123456789012:function:echo-lambda",
"Payload": {
"item.$": "$",
"token.$": "$$.Task.Token"
}
},
"Resource": "arn:aws:states:::lambda:invoke.waitForTaskToken",
"End": true
}
}
},
"End": true
}
}
}
But this doesn't work because the ItemSelector overrides the Payload of the internal TestPass state. Is there a way to get this to work?
ETA: I figured I would try putting $$.Task.Token in ItemSelector just in case it would magically work but it ended up throwing an error because $$.Task does not exist in the context object at that level.
Example with this (invalid) configuration:
{
"StartAt": "ExampleMapState",
"States": {
"ExampleMapState": {
"Type": "Map",
"ItemsPath": "$.items",
"ItemSelector": {
"dynamic.$": "$.dynamic",
"ContextIndex.$": "$$.Map.Item.Index",
"ContextValue.$": "$$.Map.Item.Value",
"token.$": "$$.Task.Token"
},
"ItemProcessor": {
"ProcessorConfig": {
"Mode": "INLINE"
},
"StartAt": "TestPass",
"States": {
"TestPass": {
"Type": "Task",
"Parameters": {
"FunctionName": "arn:aws:lambda:us-west-2:123456789012:function:echo-lambda"
},
"Resource": "arn:aws:states:::lambda:invoke.waitForTaskToken",
"End": true
}
}
},
"End": true
}
}
}
Based on my research I don't think what I'm trying to do is possible. What I ended up implementing is a workaround. I modified the function providing input to this step function to put the dynamic info that I needed into every item in the list I am iterating over. So my step function definition now looks something like this
{
"StartAt": "ExampleMapState",
"States": {
"ExampleMapState": {
"Type": "Map",
"ItemsPath": "$.items",
"ItemProcessor": {
"ProcessorConfig": {
"Mode": "INLINE"
},
"StartAt": "TestPass",
"States": {
"TestPass": {
"Type": "Task",
"Parameters": {
"FunctionName": "arn:aws:lambda:us-west-2:123456789012:function:echo-lambda",
"Payload": {
"item.$": "$",
"token.$": "$$.Task.Token"
}
},
"Resource": "arn:aws:states:::lambda:invoke.waitForTaskToken",
"End": true
}
}
},
"End": true
}
}
}
And an example input to this step function looks like:
{
"dynamic": "info",
"items": [
{
"dynamic": "info",
"resize": "true",
"format": "jpg"
},
{
"dynamic": "info",
"resize": "false",
"format": "png"
},
{
"dynamic": "info",
"resize": "true",
"format": "jpg"
}
]
}
It's not great because I have to repeat info into every item ahead of time but it works.
I have been working on step functions for a couple of weeks now. I am using map state in my step functions to iterate over an array. The array has an additional inner array as well, thus I would like to employ an addition map step in the "outer" map state. AWS documentation does not go into this level of details (as of now), therefore, I wanted to share that I managed to make it work.
This is how I managed to nest map steps:
"OuterMapState": {
"Type": "Map",
"ItemsPath": "$.shipped",
"MaxConcurrency": 0,
"Iterator": {
"StartAt": "Validate",
"States": {
"Validate": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:123456789012:function:ship-val",
"Next": "InnerMapState"
},
"InnerMapState": {
"Type": "Map",
"ItemsPath": "$.shipped.innerArray",
"MaxConcurrency": 0,
"Iterator": {
"StartAt": "doSomething",
"States": {
"doSomething": {
"Type": "Pass",
"End": true
}
}
}
},
"End": true
}
},
"End": true
}
Good luck on using AWS Step functions.
I'm sure someone will point me to an immediate solution, but I've been at this for hours, so I'm just going to ask.
I cannot get a State Machine to accept an initial input. The intent is to set up an EventBridge trigger pointed at the State Machine with a static JSON passed to the SM to initiate with the proper parameters. In development, I'm just using Step Functions option to pass a JSON as the initial input when you select "New Execution".
This is the input:
{"event":{
"country": "countryA",
"landing_bucket": "aws-glue-countryA-inputs",
"landing_key": "countryA-Bucket/prefix/filename.csv",
"forecast_bucket": "aws-forecast-countryA",
"forecast_key": "inputs/",
"date_start": "2018-01-01",
"validation": "False",
"validation_size": 90
}
}
When looking at what is passed at the ExecutionStarted log entry:
{
"input": {
"country": "countryA",
"landing_bucket": "aws-glue-countryA-inputs",
"landing_key": "countryA-Bucket/prefix/filename.csv",
"forecast_bucket": "aws-forecast-countryA",
"forecast_key": "inputs/",
"date_start": "2018-01-01",
"validation": "False",
"validation_size": 90
}
,
"inputDetails": {
"truncated": false
},
"roleArn": "arn:aws:iam::a-valid-service-role"
}
This is the State Machine:
"Comment": "A pipeline!",
"StartAt": "Invoke Preprocessor",
"States": {
"Invoke Preprocessor": {
"Type": "Task",
"Resource": "arn:aws:states:::lambda:invoke",
"InputPath": "$.input",
"Parameters": {
"FunctionName": "arn:aws:lambda:my-lambda-arn:$LATEST"
},
"Next": "EndSM"
},
"EndSM": {
"Type": "Pass",
"Result": "Ended",
"End": true
}
}
}
I've tried nearly anything I can think of from changing the InputPath to assigning the "input" dictionary directly to a variable:
"$.event":"$.input"
To drilling down to the individual variables and assigning those directly like:
"$.country:"$.country". I've also used the new Step Functions Data Flow Simulator and can't get anywhere. If anyone has any thoughts, I'd really appreciate it.
Thanks!
Edited for correct solution:
You need to set the Payload.$ parameter to $. That will pass in the entire input object to the lambda.
{
"Comment": "A pipeline!",
"StartAt": "Invoke Preprocessor",
"States": {
"Invoke Preprocessor": {
"Type": "Task",
"Resource": "arn:aws:states:::lambda:invoke",
"Parameters": {
"FunctionName": "arn:aws:lambda:my-lambda-arn:$LATEST",
"Payload.$": "$"
},
"Next": "EndSM"
},
"EndSM": {
"Type": "Pass",
"Result": "Ended",
"End": true
}
}
}
Another thing you could do is specify the input in the parameters, this will allow you to specify only all/certain parts of the json to pass in.
{
"Comment": "A pipeline!",
"StartAt": "Invoke Preprocessor",
"States": {
"Invoke Preprocessor": {
"Type": "Task",
"Resource": "arn:aws:states:::lambda:invoke",
"InputPath": "$",
"Parameters": {
"FunctionName": "arn:aws:lambda:my-lambda-arn:$LATEST",
"input_event.$": "$.event"
},
"Next": "EndSM"
},
"EndSM": {
"Type": "Pass",
"Result": "Ended",
"End": true
}
}
}
From the code perspective you could just reference it like so (python):
input = event['input_event']
I have the below state machine. The requirement is to have a lambda to query DB and get all the ids. Next I have a parallel state call that calls more than five lambdas at once. Instead of passing all the ids fetched to all the lambdas, I need to pass the respective ids to each lambda.
In the below state language, first call is DB_CALL, lets say it returns {id1, id2, id3, id4, id5, id6}, I want to pass only id1 to First_Lambda and id2 to Second_Lambda etc...
The entire id object should get passed to all lambdas. Please suggest a way to achieve this.
{
"Comment": "Concurrent Lambda calls",
"StartAt": "StarterLambda",
"States": {
"StarterLambda": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:123456789012:function:DB_CALL",
"Next": "ParallelCall"
},
"State": {
"ParallelCall": {
"Type": "Parallel",
"End": true,
"Branches": [
{
"StartAt": "First",
"States": {
"First": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:123456789012:function:First_Lambda",
"TimeoutSeconds": 120,
"End": true
}
}
},
{
"StartAt": "Second",
"States": {
"Second": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:123456789012:function:Second_Lambda",
"Retry": [ {
"ErrorEquals": ["States.TaskFailed"],
"IntervalSeconds": 1,
"MaxAttempts": 2,
"BackoffRate": 2.0
} ],
"End": true
}
}
},
{
"StartAt": "Third",
"States": {
"Third": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:123456789012:function:Third_Lambda",
"Catch": [ {
"ErrorEquals": ["States.TaskFailed"],
"Next": "CatchHandler"
} ],
"End": true
},
"CatchHandler": {
"Type": "Pass",
"Resource": "arn:aws:lambda:us-east-1:123456789012:function:CATCH_HANDLER",
"End": true
}
}
},
{
"StartAt": "Fourth",
"States": {
"Fourth": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:123456789012:function:Fourth_Lambda",
"TimeoutSeconds": 120,
"End": true
}
}
},
{
"StartAt": "Fifth",
"States": {
"Fifth": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:123456789012:function:Fifth_Lambda",
"TimeoutSeconds": 120,
"End": true
}
}
},
{
"StartAt": "Sixth",
"States": {
"Sixth": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:123456789012:function:Sixth_Lambda",
"TimeoutSeconds": 120,
"End": true
}
}
}
}
]
}
}
}
}
You can use Step Function parameter option.
This would allow you to send specific value or json to next lambda.
"Parameters": {
"toprocess.$": "$.MetaData.CorrelationId"
},
So input to this lambda would be smaller dto than compared to you first lambda. So while returning value from this lambda avoid assigning it back to Step function result.
"OutputPath": "$",
"ResultPath": "$.PartialResutl",
What you are looking for is the Map State. With this state, you pass in the iterator, in your case the path to the ids. The map state will run once for each item in the list. Within the map state, you have a full state machine, so you can call a Lambda or any other state. It has controls to limit how many are running at once if that is needed.
I am writing an AWS step function, and for one of the steps, I wish to call a lambda that accepts an array as one of the inputs. However, if I try to pass in a JsonPath into the array, I get
The value for the field 'arrayField.$' must be a STRING that contains a JSONPath but was an ARRAY
My step function definition:
{
"StartAt": "First",
"States": {
"First": {
"Type": "Pass",
"Parameters": {
"type": "person"
},
"ResultPath": "$.output",
"Next": "Second"
},
"Second": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:<aws_id>:function:MyFunction",
"Parameters": {
"regularParameter": "some string",
"arrayParameter.$": ["$.output.type"]
},
"Next": "Succeed"
},
"Succeed": {
"Type": "Succeed"
}
}
}
How can I use jsonPath inside the array?
Since a new release you could use the intrinsic function States.Array:
"arrayParameter.$": "States.Array($.output.type)"
https://docs.aws.amazon.com/step-functions/latest/dg/amazon-states-language-intrinsic-functions.html
As #Seth Miller mentioned JsonPath resolution within arrays doesn't work unfortunately. If the amount of values to replace in the array is small and known there's a simple workaround (in my case I needed an array of size 1).
The steps are:
Initialise the array with the number of values you need;
Replace each value using "ResultPath": "$.path.to.array[n]";
Use "$.path.to.array" in your task.
Simple, working example:
{
"StartAt": "First",
"States": {
"First": {
"Type": "Pass",
"Parameters": {
"type": "person"
},
"ResultPath": "$.output",
"Next": "Initialise Array"
},
"Initialise Array": {
"Comment": "Add an entry for each value you intend to have in the final array, the values here don't matter.",
"Type": "Pass",
"Parameters": [
0
],
"ResultPath": "$.arrayParameter",
"Next": "Fill Array"
},
"Fill Array": {
"Comment": "Replace the first entry of array with parameter",
"Type": "Pass",
"InputPath": "$.output.type",
"ResultPath": "$.arrayParameter[0]",
"End": true
}
}
}
And to use the resulting array in your task example:
"Second": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:<aws_id>:function:MyFunction",
"Parameters": {
"regularParameter": "some string",
"arrayParameter.$": "$.arrayParameter"
},
"Next": "Succeed"
},
Another way to approach this is by using Parallel state that outputs an array of objects and then use jsonPath to convert it to a simple array:
{
"StartAt": "Parallel",
"States": {
"Parallel": {
"Type": "Parallel",
"Next": "Use Array",
"ResultPath": "$.items",
"Branches": [
{
"StartAt": "CreateArray",
"States": {
"CreateArray": {
"Type": "Pass",
"Parameters": {
"value": "your value"
},
"End": true
}
}
}
]
},
"Use Array": {
"Type": "Pass",
"Parameters": {
"items.$": "$.items[*].value"
},
"End": true
}
}
}
In this example, Parallel state outputs the following json:
{
"items": [
{
"value": "your value"
}
]
}
And "Use Array" state produces:
{
"items": [
"your value"
]
}
JSONPath inside parameters field need to be a string. So if you want to pass to lambda function a parameter called arrayParameter, you´ll need to make a jsonPath query that extract that array.
For example, if inside the key output is a key called outputArray with the array as its value.
Input JSON:
{
"pre": "sdigf",
"output": {
"result": 1,
"outputArray": ["test1","test2","test.."]
}
}
The parameter sintax:
"arrayParameter.$": "$.output.outputArray"
Reasonable advice
I ran into a use case for JsonPath resolution within arrays today and found (like you have) that the functionality does not exist today. I ended up deciding that doing the data massaging in code was simpler and cleaner. For example, you could create a small Lambda that takes in the object emitted by First and massages it to a format acceptable to Second and adds it to the output (WaterKnight mentions this solution in a comment to another question).
This assumes that you are, for some reason, unable to change the format of the input to that Lambda in Second (which would be the absolute shortest path here).
Unreasonable advice
That said, if you want a way to do this completely within Step Functions that is fairly gross, you can use the result of a Map state that executes Pass states. The output of the Map state is an array that aggregate the output of each constituent Pass state. These Pass states simply emit the value(s) you want in the final array using the Parameters attribute. An example Step Function definition follows. I did warn that it is gross and that I went a different way to solve the problem.
{
"StartAt": "First",
"Comment": "Please don't actually do this",
"States": {
"First": {
"Type": "Pass",
"Parameters": {
"type": "person"
},
"ResultPath": "$.output",
"Next": "Add Array"
},
"Add Array": {
"Comment": "A Map state needs some array to loop over in order to work. We will give it a dummy array. Add an entry for each value you intend to have in the final array. The values here don't matter.",
"Type": "Pass",
"Result": [
0
],
"ResultPath": "$.dummy",
"Next": "Mapper"
},
"Mapper": {
"Comment": "Add a Pass state with the appropriate Parameters for each field you want to map into the output array",
"Type": "Map",
"InputPath": "$",
"ItemsPath": "$.dummy",
"Parameters": {
"output.$": "$.output"
},
"Iterator": {
"StartAt": "Massage",
"States": {
"Massage": {
"Type": "Pass",
"Parameters": {
"type.$": "$.output.type"
},
"OutputPath": "$.type",
"End": true
}
}
},
"ResultPath": "$.output.typeArray",
"Next": "Second"
},
"Second": {
"Comment": "The Lambda in your example is replaced with Pass so that I could test this",
"Type": "Pass",
"Parameters": {
"regularParameter": "some string",
"arrayParameter.$": "$.output.typeArray"
},
"Next": "Succeed"
},
"Succeed": {
"Type": "Succeed"
}
}
}
As many answers correctly pointed out, it's not possible to do it exactly the way you need. But I would suggest another solution: an array of dictionaries. It's not exactly what you need, but is native and not hacky.
"Second": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:<aws_id>:function:MyFunction",
"Parameters": {
"regularParameter": "some string",
"arrayParameter": [{"type.$": "$.output.type"}]
},
"Next": "Succeed"
},
The result would be
{
"regularParameter": "some string",
"arrayParameter": [{"type": "SingleItemWrappedToAnArray"}]
}