使用 AWS Step Functions 靈活調度 AWS Lambda (Level:200)

© 2018, Amazon Web Services, Inc. or its affiliates. All rights reserved.
Scott Li
Cloud Support Engineer, Amazon Web Services
Orchestrating AWS Lambda with
Step Functions

Modern
Serverless
App

The Twelve-Factor App
VI. Process
Execute the app as one or more stateless
processes
…Lambda functions should always be
treated as being stateless, despite the
ability to potentially store some
information locally between execution
environment re-use
…. You should always store any stateful
information in a database, cache, or
separate data store via a backing service.

“I want to sequence functions”

“I want to select functions based on data”
?

“I want to run functions in parallel”

“I want to retry
functions”
“I want try / catch /
finally”
“I have code that runs for hours”

Coordination by Function Chaining

Coordination by Database

Coordination by Message Queues

Coordination Must-Haves
Scales Out Does Not Lose
State
Handles
Errors/Timeouts
Easy to Build/Operate Auditable

AWS Step Functions

A Step Function is a state machine
Changing to a specified state when reading an input
What is AWS Step Functions?

Application Lifecycle in AWS Step Functions
Define in JSON

Visualize in the Console

Monitoring Executions

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

Take States: Pull or Push
AWS Lambda
…On-premises
Amazon Elastic Compute Cloud (EC2),
Amazon Elastic Container Service (ECS)
, or… Long poll
Push

Take States: Dispatch Work
{
"StartAt": "HelloWorld",
"States": {
"HelloWorld": {
"Type": "Task",
"Resource":"arn:aws:lambda:REGION:
ACCOUNT_ID:function:FUNCTION_NAME",
"End": true
}
}
}

Retry Failures of Take States
"HelloWorld": {
"Type": "Task",
…
"Retry": [
{
"ErrorEquals": [”States.TaskFailed"],
"IntervalSeconds": 1,
"MaxAttempts": 3,
"BackoffRate": 2.0
},
… ]
1st retry after: 1 x 2^0 =1 sec
2nd retry after: 1 x 2^1 = 2 sec
3rd retry after: 1 x 2^2 = 4 sec

Catch Failures of Take States
"HelloWorld": {
"Type": "Task",
… "Catch":[
{
"ErrorEquals": [" States.TaskFailed"],
"Next": "ReservedTypeFallback "
},
{
"ErrorEquals": ["AccountAlreadyExistsException"],
"Next": " CustomErrorFallback"
… ]
{

Function Error Handling: Python
{
"StartAt": "Create Account",
"States": {
"CreateAccount": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:123456789012:function:CreateAccount",
"Next": "Send Welcome Email",
"Catch": [
{
"ErrorEquals": ["AccountAlreadyExistsException"],
"Next": "SuggestAccountName"
}
]
},
…
}
def create_account(event, context):
class AccountAlreadyExistsException(Exception):
pass
raise AccountAlreadyExistsException('Account is in use!')

Input and Output Processing
• State Input
{
"name": "dog",
"metadata":{
"extension": "jpg",
"size": "1mb"
},
"status": "pending",
}
• InputPath
• $ (ALL) / $.metadata
• ResultPath
• $."status" è "status": "finished",
• OutputPath
$ (ALL)
"finished"

Choice State for Branching Logic
"ChoiceState": {
"Type" : "Choice",
"Choices": [
{
"Variable": "$",
"StringEquals": "FirstState",
"Next": "FirstMatchState"
},
{
"Variable": "$.sequence",
"NumericEquals": 2,
"Next": ”SecondMatchState"
… ]

Parallel States to Fork and Join Processes
"Parallel": {
"Type": "Parallel",
"Next": "Final State",
"Branches": [
{
"StartAt": "Wait 20s",
"States": {
"Wait 20s": {
"Type": "Wait",
"Seconds": 20,
"End": true
}
... ]

Wait State For Timed Delay
"wait_using_seconds": {
"Type": "Wait",
"Seconds": 10,
"Next": "wait_using_timestamp"
},
"wait_using_timestamp": {
"Type": "Wait",
"Timestamp": "2018-06-
04T01:59:00Z",
"Next": "wait_using_timestamp_path"
},
…

Using Templates or Building from Scratch

Tips
• Don’t try/catch too much at the Lambda level. Use it at Step Functions
• Use Timeouts to avoid stuck executions
• Use ARNs instead of passing large payloads
• Avoid reaching the history limit

Integrate with Other AWS services
• Create state machines and Activities with
AWS CloudFormation
• Call AWS Step Functions with Amazon APIGateway
• 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

Image Recognition and Processing Backend

Amazon EBS Snapshot Management
Ireland Ohio

DEMO

CoCa-Cola Company: Vending Pass Program

How much?
per thousand
state transitions
Using US East (N. Virginia)
4,000 free
transitions/month
$0.0250
Free tier:

Pricing Example
Total State Transitions:
3 state transitions per execution x
100,000 executions = 300,000 state transitions
Monthly Charges:
300,000 state transitions x
$0.000025 per state transition = *$7.50 per month
*Using US East (N. Virginia) price,
less free tier adjustment of 4,000 free state transitions per month.
$7.5 – (4000x 0.000025) =
$7.40

The Benefit of AWS Step Functions
Build Applications Quickly Scale and Recover Reliably Evolve Applications Easily

Thank you!

使用 AWS Step Functions 靈活調度 AWS Lambda (Level:200)

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