Adrienne Tacke PRO
🇵🇭 Software Engineer & Sr. Developer 🥑 @ Cisco • Published Author • LinkedIn Learning Instructor • Twitch Streamer 🕹 Most important: I spend way too much money on desserts and endless hours playing Borderlands
IDEMPOTENCY
One Serverless Principle to Rule Them All
Moar Serverless!!! 2022
@AdrienneTacke
@AdrienneTacke
IDEMPOTENCY
-- One Serverless Principle to Rule Them All
Agenda
idempotency
Not a real word,
according to Merriam-Webster.
idempotent
idem·po·tent : relating to or being a mathematical quantity which when applied to itself under a given binary operation equals itself
Merriam-Webster
idempotent
i·dem·po·tent : unchanged when multiplied by itself
Random House Webster's
idempotency
i·dem·po·ten·cy : characteristic that ensures when running an operation over and over, and given the same input, that the same output is achieved every single time.
Adrienne and other developers
"...when multiplied by itself"
"unchanged"
〞
Great, what does
have to do with good serverless architecture?
– Curious Moar Serverless Attendee
〞
Have you heard about the seven design principles of well-architected applications?
– Me, Adrienne
seven design principles of well-architected applications*
* Source: https://docs.aws.amazon.com/wellarchitected/latest/serverless-applications-lens/general-design-principles.html
🧱 Speedy, simple, singular
🔀 Think concurrent requests, not total requests
🙅🏻♀️ Share Nothing
💽 Assume no hardware affinity
🚦 Orchestrate your application with state machines, not functions
📨 Use events to trigger transactions
☔ Design for failures and Duplicates
seven design principles of well-architected applications*
* Source: https://docs.aws.amazon.com/wellarchitected/latest/serverless-applications-lens/general-design-principles.html
🧱 Speedy, simple, singular
🔀 Think concurrent requests, not total requests
🙅🏻♀️ Share Nothing
💽 Assume no hardware affinity
🚦 Orchestrate your application with state machines, not functions
📨 Use events to trigger transactions
☔ Design for failures and Duplicates
Impossible without idempotency!
☔ Design for failures and Duplicates
Failures
retries
lead to
.
retries
means
duplicates
can and will occur.
Implementing
Failures
lead to
.
retries
duplicates
If
exist,
is key to mitigate side effects.
idempotency
retries
means
can and will occur.
Implementing
Failures
lead to
.
retries
duplicates
side effects
side effects
side effects
side effects
side effects
side effects
side effects
side effects
side effects
side effects
side effects
side effects
side effects
side effects
side effects
side effects
side effects
side effects
side effects
side effects
side effects
What happens without idempotency?
Order 🍰
Order placed
Order processed
Adrienne
Adrienne
Website
Website
API
API
What happens without idempotency?
Adrienne enters tunnel
Adrienne exits tunnel
Network failure
Time
Adrienne
Adrienne
Website
Website
API
API
Adrienne exits tunnel
Network failure
What happens without idempotency?
Time
Adrienne
Adrienne
Website
Website
API
API
Adrienne exits tunnel
Adrienne sees error and resubmits order
Order 🍰
Order placed
Order processed
🚚 Cake is on the way!
What happens without idempotency?
Time
Order 🍰
Order placed
Order processed
🚚 Cake is on the way!
Adrienne
Adrienne
Website
Website
API
API
What happens without idempotency?
Adrienne sees error and resubmits order
Network failure
Order 🍰
Order placed
Order processed
Adrienne enters tunnel
Adrienne exits tunnel
🚚 Also, this first cake is on the way!
Time
Surprise!
Order 🍰
Order placed
Order processed
🚚 Cake is on the way!
Adrienne
Adrienne
Website
Website
API
API
What happens without idempotency?
Adrienne sees error and resubmits order
Network failure
Order 🍰
Order placed
Order processed
Adrienne enters tunnel
Adrienne exits tunnel
🚚 Also, this first cake is on the way!
Time
Surprise!
side effect:
duplicate requests are considered valid requests
How do we apply idempotency?
How do we apply idempotency?
elements of idempotency
idempotency key
Generated by caller, unique identifier, captures intent
How do we apply idempotency?
idempotency key
idempotency layer
Generated by caller, unique identifier, captures intent
Acts like a filter, decides what to do with a request
elements of idempotency
How do we apply idempotency?
idempotency key
idempotency layer
persistent storage
Generated by caller, unique identifier, captures intent
Acts like a filter, decides what to do with a request
Stores state, "source of truth" for idempotency keys, list of checkpoints in retries
elements of idempotency
How do we apply idempotency?
idempotency key
idempotency layer
persistent storage
Stores state, "source of truth" for idempotency keys, list of checkpoints in retries
Acts like a filter, decides what to do with a request
Generated by caller, unique identifier, captures intent
elements of idempotency
How do we apply idempotency?
Generate unique identifier
Adrienne
placeOrder(event) {
const context = event.context;
const message = event.data;
const order = {
id: context.eventId,
timestamp: context.timestamp,
cake: message.data
? Buffer.from(message.data, 'base64').toString()
: '',
idempotencyKey: "cb3d3141-a229-6ce0-b005-eb832e2cdabc"
};
// Remaining request logic
}
"cb3d3141-a229-6ce0-b005-eb832e2cdabc"
placeOrder(event)
How do we apply idempotency?
Adrienne
placeOrder(event)
API
Persistent Store
Run placeOrder handler(event)
Initial Request
Get idempotency key (event)?
Nothing found
Set idempotency key + handler result
Response not received by client
❌
How do we apply idempotency?
Adrienne
placeOrder(event)
API
Persistent Store
Run placeOrder handler(event)
Initial Request
Get idempotency key (event)?
Nothing found
Set idempotency key + handler result
Response not received by client
❌
Subsequent requests
(retries)
Get idempotency key (event)?
Exists: return result from initial request
Response sent to client
placeOrder(event)
Idempotency libraries and tools
Idempotency libraries and tools
✨ Features
- Prevent multiple Lambda handler function executions on the same payload during a time window.
- Reuse the same DynamoDB table to store idempotency state. Function name is added in addition to the idempotency key as a hash key.
- Set expiration period for idempotency records.
- Ensure Lambda handler returns the same result when called with the same payload.
Java, Python
# Idempotent decorator
from aws_lambda_powertools.utilities.idempotency import (
DynamoDBPersistenceLayer, idempotent
)
persistence_layer = DynamoDBPersistenceLayer(table_name="IdempotencyTable")
@idempotent(persistence_store=persistence_layer)
def handler(event, context):
payment = create_subscription_payment(
user=event['user'],
product=event['product_id']
)
...
return {
"payment_id": payment.id,
"message": "success",
"statusCode": 200,
}🔑 Idempotency Key
hash representation of entire event or specific configured subset of the event
💾 Persistent Storage
Amazon DynamoDB (only supported persistent storage layer for now)
Other great tools and libraries!
Stripe API - Supports idempotent requests and implements idempotency keys.
https://stripe.com/blog/idempotency
IdempotentAPI - Performs additional idempotency checks. NuGet package.
https://www.nuget.org/packages/IdempotentAPI
https://stripe.com/docs/api/idempotent_requests
Step Functions - Serverless orchestration service.
https://docs.aws.amazon.com/step-functions
https://www.dotnetnakama.com/blog/idempotency-for-fault-tolerant-web-apis
Durable Functions - Azure's serverless orchestration service.
https://docs.microsoft.com/en-us/azure/azure-functions/durable/durable-functions-overview
IDEMPOTENCY
One Serverless Principle to Rule Them All
@AdrienneTacke
Thank you Moar Serverless!!!
One Serverless Principle to Rule Them All: Idempotency
By Adrienne Tacke
