AWS Step Functions is a new, fully-managed service that makes it easy to coordinate the components of distributed applications and microservices using visual workflows. Step Functions is a reliable way to connect and step through a series of AWS Lambda functions so that you can build and run multi-step applications in a matter of minutes. This session shows how to use AWS Step Functions to create, run, and debug cloud state machines to execute parallel, sequential, and branching steps of your application, with automatic catch and retry conditions.

1. ©2017, Amazon Web Services, Inc. or its affiliates. All rights reserved
Serverless Apps with
AWS Step Functions
Chris Munns – Senior Developer Advocate - Serverless

2. About me:
Chris Munns - munns@amazon.com, @chrismunns
• Senior Developer Advocate - Serverless
• New Yorker
• Previously:
• Business Development Manager – DevOps, July ’15 - Feb ‘17
• AWS Solutions Architect Nov, 2011- Dec 2014
• Formerly on operations teams @Etsy and @Meetup
• Little time at a hedge fund, Xerox and a few other startups
• Rochester Institute of Technology: Applied Networking and
Systems Administration ’05
• Internet infrastructure geek

3. λλ
λ DBMS
λ
λ
λ
λ
λ
λ λ
λ
λ
Queue
Modern
Serverless
app

4. Modern
Serverless
app

5. “I want to sequence functions”
“I want to select functions based on data”
“I want to retry functions”
“I want try/catch/finally”
Functions into apps
“I have code that runs for hours”
“I want to run functions in parallel”

7. Coordination by method call
λ λ
λ
λ
λ
λ
λ

8. Coordination by function chaining
λ
λ
λ
λ
λλ
λ

9. Coordination by database
λλ
λ
λ
λλ
λ

10. Coordination by queues
λ
λ
λ
λ λλ
λ

11. Coordination must-haves
• Scales out
• Doesn’t lose state
• Deals with errors/timeouts
• Easy to build & operate
• Auditable

13. “State Machine”(noun)
1. A concept used by CompSci
profs for torturing
undergrads, full of arcane
math.
2. A practical way to build and
manage modern Serverless
Cloud apps.
Dictionary

14. “I want to sequence functions”
AWS Step Functions, we can easily change and iterate on
the application workflow of our food delivery service in
order to optimize operations and continually improve
delivery times. AWS Step Functions lets us dynamically
scale the steps in our food delivery algorithm so we can
manage spikes in customer orders and meet demand.
Mathias Nitzsche, CTO, foodpanda
“

17. var Twit = require('twit');
var T = new Twit(require('botfiles/config.js'));
exports.handler = function myBot(event, context, callback) {
var list = event.inputList;
var textToTweet = list.shift();
var output = { inputList: list }
T.post('statuses/update',
{ status: textToTweet }, function(err, reply) {
if (err) {
console.log('error:', err); context.fail();
} else {
console.log('tweet:', reply); callback(null, output);
}
});
};

18. How it works – API-level
Create State Machine – input is a
machine spec in a JSON DSL
Run Machine – input JSON blob,
returns Execution ID
List Executions
Describe Execution
Stop Execution

20. https://states-language.net/spec

22. “I want to select functions based on data”
“With AWS Step Functions, it was easy to build a multi-step product
updating system to ensure our database and website always have the
latest price and availability information.
AWS Step Functions let us replace a manual updating process with an
automated series of steps, including built-in retry conditions and error
handling, so we can reliably scale before a big show, and keep pace
with rapidly changing fashions.”
Jared Browarnik, CTO, TheTake
“

24. "ChoiceState": {
"Type" : "Choice",
"Choices": [
{
"Variable": "$.productSource",
"StringEquals": "screen-scrape",
"Next": "ScreenScrapeState"
},{
"Variable": "$.productSource",
"StringEquals": "vendor-a",
"Next": "VendorA"
},{
"Variable": "$.productSource",
"StringEquals": "vendor-b",
"Next": "VendorB"
},
{
"Variable": "$.productSource",
"StringEquals": "vendor-c",
"Next":"VendorC"
},{
"Variable": "$.productSource",
"StringEquals": "updateProduct",
"Next":"UpdateProduct"
}
],
"Default": "ScreenScrapeState”
}

25. “I want to retry functions”
We get transient errors from a RESTful
service we depend on, once every four
or five times we call it. But if we keep
retrying, it eventually works.
“

26. {
"Comment": "Call out to a RESTful service",
"StartAt": "Call out",
"States": {
"Call out": {
"Type": "Task",
"Resource":
"arn:aws:lambda:eu-central-1:123456789012:function:RestCallout",
"Retry": [
{ "ErrorEquals": [ "HandledError" ], "MaxAttempts": 10 }
],
"End": true
}
}
}

27. “I want to run functions in parallel”
We want to send the captured image to
three OCR providers and take the result
with the highest confidence value.“

29. "Send for OCR": {
"Type": "Parallel",
"Next": "Pick result",
"Branches": [
{
"StartAt": "Prep1",
"States": {
"Prep1": {
"Type": "Pass",
"Result": { "inputList": [ "OCR Provider 1" ] },
"Next": "Go1"
},
"Go1": {
"Type": "Task",
"Resource": "arn:aws:lambda:eu-central-1:123456789012:function:StatesBot",
"End": true
}
}

30. Where does transient application
state live?
In the machine, in JSON texts
passing from state to state.A:
Q:

31. Input processing
{
"title": "Numbers to add",
"numbers": [ 3, 4 ]
}
{
"Type": "Task",
"InputPath": "$.numbers",
"Resource": "arn:aws:lambda…"
…
[ 3, 4 ]
Raw input:
State spec:
Task input:

32. Input processing
Q: InputPath not provided?
A: State gets raw input as-is.
Q: InputPath is null?
A: State gets an empty JSON object: {}
Q: InputPath produces plural output?
A: State gets it wrapped in a JSON array.

33. Result placement
{
"title": "Numbers to add",
"numbers": [ 3, 4 ]
}
{
"Type": "Task",
"InputPath": "$.numbers",
"ResultPath": "$.sum”,
…
Raw input:
State spec:
Output: {
"title": "Numbers to add",
"numbers": [ 3, 4 ],
”sum": 7
}

34. Result placement
Q: ResultPath not provided?
A: Input discarded, raw output used.
Q: ResultPath is null?
A: State input is state output.
Q: ResultPath produces plural output?
A: Not allowed, validator won’t accept.

35. “I want try/catch/finally”
AWS Step Functions makes it simple to coordinate information
from many different infrastructure systems using easy to design
workflows and create a more intelligent monitoring system for our
Platform as a Service (PaaS).
With AWS Step Functions, we can reliably automate monitoring
decisions and actions in order to reduce human intervention by
over 60%, which improves infrastructure operation productivity and
customer application availability on our platform.
Pedro Pimenta, VP R&D, OutSystems
“

36. 13 AWS Lambda Task States
6 Choice States
1 Fail State
“I want try/catch/finally”

38. "Access Media": {
"Type": "Task",
"Resource": "arn:aws:lambda:eu-central-1:123456789012:function:FindMedia",
"TimeoutSeconds": 2,
"Next": "Graceful Exit",
"Retry": [
{
"ErrorEquals": [ "States.Timeout" ],
"IntervalSeconds": 2, "MaxAttempts": 2, "BackoffRate": 1.5
}
],
"Catch": [
{ "ErrorEquals": [ "States.ALL" ], "Next": "Clean Up" }
]
},

39. “I have code that runs for hours”
We need to gather data from our
production line, in units of 8-hour shifts.
“

40. More APIs
Register Activity Task - Returns ARN
Poll For task (by ARN)
Report Success
Report Failure
Report Heartbeat

41. "NextShift": {
"Type": "Wait",
"TimestampPath": "$.ShiftStart",
"Next": "Gather Plant Data"
},
"Gather Plant Data": {
"Type": "Task",
"Resource":
"arn:aws:states:ap-northeast-1:123456789012:activity:PlWatch",
"TimeoutSeconds": 30000,
"HeartBeatSeconds": 120,
"Next": "Clean up"
}

42. “I want to sequence functions”
“I want to select functions based on data”
“I want to retry functions”
“I want try/catch/finally”
Is this you?
“I have code that runs for hours”
“I want to run functions in parallel”

43. Integrate with other AWS services
• Create state machines and Activities with AWS
CloudFormation
• Call AWS Step Functions with Amazon API Gateway
• Monitor state machine executions with Amazon CloudWatch
• Log API calls with AWS CloudTrail

44. Serverless Human Approval Tasks
https://aws.amazon.com/blogs/compute/
implementing-serverless-manual-approval-steps-in-aws-step-functions-and-amazon-api-gateway/

45. Image Recognition and Processing Backend
Task
Choice
Fail
Parallel
https://github.com/awslabs/lambda-refarch-imagerecognition

47. 2.5¢
How much?
per thousand
state transitions
4,000 free
transitions/month
Free tier:

48. (Demo)

49. Chris Munns
munns@amazon.com
@chrismunnshttps://www.flickr.com/photos/theredproject/3302110152/

50. ?
https://secure.flickr.com/photos/dullhunk/202872717/