AWS Builders' Days

1. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Building Advanced Serverless
Applications with AWS Step Functions
Danilo Poccia
Technical Evangelist
danilop@amazon.com
@danilop
danilop

2. λλ
λ DBMS
λ
λ
λ
λ
λ
λ λ
λ
λ
Queue
Modern
serverless
app

3. Modern
serverless
app

4. "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"

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

6. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.

7. Application Lifecycle in AWS Step Functions
Visualize in the
Console
Define in JSON Monitor
Executions

8. Define in JSON and Then Visualize in the Console
{
"Comment": "Hello World Example",
"StartAt" : "HelloWorld",
"States" : {
"HelloWorld" : {
"Type" : "Task",
"Resource" : "${lambdaArn}",
"End" : true
}
}
}

9. Execute One or One Million
Start
End
HelloWorld
Start
End
HelloWorld
Start
End
HelloWorld
Start
End
HelloWorld
Start
End
HelloWorld
Start
End
HelloWorld
Start
End
HelloWorld
Start
End
HelloWorld

10. Maximum Execution Time
AWS Lambda
Functions
5 minutes
AWS Step Functions
State Machines
1 year

11. Monitor Executions from the Console

12. Seven State Types
Task A single unit of work
Choice Adds branching logic
Parallel Fork and join the data across tasks
Wait Delay for a specified time
Fail Stops an execution and marks it as a failure
Succeed Stops an execution successfully
Pass Passes its input to its output

13. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
ExtractImageMetadata
ImageTypeCheck
TransformMetadata
Rekognition Thumbnail
StoreMetadata
Start
End
Synchronous task
Task: a single unit of work
Synchronous: Lambda
{
"ExtractImageMetadata": {
"Type": "Task",
"Resource": "arn:aws:lambda:mars-ter …",
…
}
}

14. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
ExtractImageMetadata
TransformMetadata
Rekognition Thumbnail
StoreMetadata
Start
End
Task: a single unit of work
Asynchronous: "Activity Task", Polled by workers
{
"ExtractImageMetadata": {
"Type": "Task",
"Resource": "arn:aws:states:mars-ter …",
…
}
}
Asynchronous task

15. API actions on activity task
Register Activity Task - Returns ARN
Poll For task (by ARN)
Report Success
Report Failure
Report Heartbeat

16. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
https://states-language.net/spec.html

17. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Integrate with other AWS services
• Create state machines and activities with AWS CloudFormation
• Call AWS Step Functions with Amazon API Gateway
• Start state machines in response to events, or on a schedule,
with Amazon CloudWatch Events
• Monitor state machine executions with Amazon CloudWatch
• Log API calls with AWS CloudTrail
• Start state machine using AWS Lambda

18. Build Visual Workflows from State Types
Task
Choice
Fail
Parallel

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

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

21. Amazon EBS Snapshot Management
https://github.com/awslabs/aws-step-functions-ebs-snapshot-mgmt
1. Tag
2. Count
3. Copy to DR region
4. Delete Expired
Whenever a new EBS
snapshot completes:
State Machines
invoked by Amazon
CloudWatch Events

22. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Demo:
AWS Step Functions

23. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.

24. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.© 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Case Studies

25. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Vending Pass problem
1. Thirsty consumer presents
card, can buy a drink with
Vending Pass or debit
2. But mobile wallet display can
get out of sync under certain
conditions
3.

26. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Vending Pass problem
• Just wait for backend
to catch up
• Create a two-step state
machine:
• Wait (90 seconds)
• Update mobile wallet
• Cheap and simple!

27. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
• Transcode 350 clips/day into
14 formats, fast
• It’s all done with FFmpeg.
The processing time is just
about 100% of the video
length
• Aargh!
Video processing problem

28. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
• Derive keyframe locations
within the source
• Split the source at the
keyframes
• Process segments (typically
0.5 sec per) in parallel
• Concatenate segments
• Elapsed time: ~20 min down
to ~2 minutes
Video processing solution

29. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Details
How to get from Lambda to Amazon S3:
ffmpeg -f concat –safe 0 -I filelist.ffcat –c copy pipe:0 |
aws s3 cp – s3://output-bucket/output-file.mp4

30. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Details

31. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Let’s peek at the code!
"Init": {
"Type": "Pass",
"ResultPath": "$.operation",
"Result": "prepare-split",
"Next": "PrepareSplit"
},
"PrepareSplit": {
"Type": "Task",
"Resource": "arn:…:ffmpeg-18HFP9FXFL6P",
"Next": "SplitPrepared"
},
"SplitPrepared": {
"Type": "Pass",
"ResultPath": "$.operation",
"Result": "perform-split",
"Next": "PerformSplit"
},
"PerformSplit": {
"Type": "Task",
"Resource": "arn:…:ffmpeg-18HFP9FXFL6P",
"Next": "SplitPerformed"
},
"SplitPerformed": {
"Type": "Pass",
"ResultPath": "$.operation",
"Result": "poll-results",
"Next": "PreparePoll"
},
"PreparePoll": {
"Type": "Pass",
"ResultPath": "$.pollstatus",
"Result": "Submitted",
"Next": "WaitForResults"
}
Hmm…the same function,
throughout

32. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Let’s peek at the code!
"WaitForResults": {
"Type": "Choice",
"Choices": [
{
"Variable": "$.pollstatus",
"StringEquals": "Complete",
"Next": "SegmentsCompleteState"
},
{
"Variable": "$.pollstatus",
"StringEquals": "Progressing",
"Next": "loop_wait_using_seconds"
},
{
"Variable": "$.pollstatus",
"StringEquals": "Submitted",
"Next": "loop_wait_using_seconds"
}
]
}
"loop_wait_using_seconds": {
"Type": "Wait",
"Seconds": 3,
"Next": "loop"
},
"loop": {
"Type": "Task",
"Resource": "arn:…:ffmpeg-18HFP9FXFL6P",
"Next": "WaitForResults"
},
"SegmentsCompleteState": {
"Type": "Pass",
"ResultPath": "$.operation",
"Result": "concat",
"Next": "CompleteState"
},
"CompleteState": {
"Type": "Task",
"Resource": " arn:…:ffmpeg-18HFP9FXFL6P",
"End": true
}
Counts the segments,
sets $.pollstatus
Stitches segments together

33. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Takeaways
Use Amazon S3
data events to
trigger parallel
Lambda
processing: win
Use Amazon
S3 URLs to
stream video to
Lambda: win
Scaling to 1,000
Lambdas, rather
than 1,000 EC2
instances: win
Process video
segments in
parallel: win

34. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
1. Sometimes Lambda is best, sometimes
ECS
2. Previously, all tied together with
pub/sub and
procedural code
3. Aargh!
Media transcoding problem

35. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
1. Use state machines to pick
execution engine
2. Use CloudWatch Events for
messaging and triggering
Step Functions
Media transcoding solution

36. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Let’s peek at the code!
"Encoder Decider": {
"Type": "Choice",
"Default": "Run ECS Encoder",
"Choices": [
{
"Next": "Run Lambda Encoder",
"And": [
{
"Variable": "$.asset.size",
"NumericLessThanEquals": 2000000000
},
{
"Variable": "$.asset.duration_ms",
"NumericLessThanEquals": 10000
}
]
}
]
}
Hmm…maybe "Default" should
have been called "Else"

37. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Let’s peek at the code!
"Run ECS Encoder": {
"Type": "Task",
"Resource": "arn:…SubmitECSTask",
"Retry": [
{
"ErrorEquals": [
"NoResourceInCluster"
],
"IntervalSeconds": 5,
"MaxAttempts": 720,
"BackoffRate": 1.0
}
],
"ResultPath": "$.task",
"Next": "Wait X Seconds"
}
Hmm…every 5 seconds,
for an hour?!
"Wait X Seconds": {
"Type": "Wait",
"SecondsPath": "$.task.wait_time",
"Next": "Get ECS Task Status"
},
"Get ECS Task Status": {
"Type": "Task",
"Resource": "arn:…ECSTaskStatus",
"Next": "ECS Task Complete?",
"ResultPath": "$.task.status"
}

38. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Let’s peek at the code!
"ECS Task Complete?": {
"Type": "Choice",
"Choices": [
{
"And": [
{
"Variable": "$.task.status",
"StringEquals": "FAILED"
},
{
"Variable": "$.task.attempt",
"NumericGreaterThanEquals": 3
}
],
"Next": "Fire Failed Event"
},
{
"Variable": "$.task.status",
"StringEquals": "FAILED",
"Next": "Run ECS Encoder"
},
{
"Variable": "$.task.status",
"StringEquals": "SUCCEEDED",
"Next": "Fire Successful Event"
}
],
"Default": "Wait X Seconds"
},
"Fire Successful Event": {
"Type": "Task",
"Resource": "aws:…SendSuccessfulEvent",
"End": true
},
"Fire Failed Event": {
"Type": "Task",
"Resource": "aws:…SendFailedEvent",
"End": true
}
These fire
CloudWatch
Events

39. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Takeaways
Passing a
correlation ID
through a complex
serverless app: win
SAM to make
code changes
auditable: win
Code Pipeline
for CI/CD: winCloudWatch
Events pattern
matching: win

40. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
More state machines
Image Recognition and Processing BackendEBS Snapshot Management
https://aws.amazon.com/step-functions/getting-started

41. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
What are you building? #stepfunctions
https://console.aws.amazon.com/states/

42. © 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.© 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Building Advanced Serverless
Applications with AWS Step Functions
Danilo Poccia
Technical Evangelist
danilop@amazon.com
@danilop
danilop