There are many software engineering practices that can and should be applied to Lambda functions: Single Responsibility Principle (from SOLID), You Ain't Gonna Need It (YAGNI), Keep It Simply Stupid (KISS). In this presentation, I'll go through the different ways to apply those principles in the AWS serverless world and even to avoid the usage of Lambda functions sometimes.

1. Less is more
Do more with less code in a serverless world
Jerome Van Der Linden
Geneva Serverless Meetup - 26/05/2020

2. About me
• In a previous life, ”Mr Cut Cut” (M. Coupe coupe)
• Developer & software craftsman
• And now, Solutions Architect @ AWS
2
linkedin.com/in/jeromevdl/
Jerome Van Der Linden

3. Few principles
Clean Code

4. SOLID
4
S Single Responsibility Principle
O Open / closed Principle
L Liskov substitution Principle
I Interface segregation Principle
D Dependency Inversion Principle

5. Single Responsibility Principle
5
“A class or module should have one,
and only one, reason to be changed”
- Robert C. Martin, aka Uncle Bob

6. YAGNI (You Ain’t Gonna Need It)
6
Just because you can,
doesn’t mean you should…

7. KISS
7

8. 8
And many more…
Clean Code
DRY
Don’t Repeat Yourself
Law of Demeter
Broken window
theory
Boy scout rule
Not invented here

9. How to apply those principles?
In the serverless world

10. Serverless World?
10
Serverless == FAASFunction As A Service

11. Serverless World?
11
Serverless ⊃ FAASFunction As A Service

12. AWS Serverless world
12
AWS
Lambda
AWS
Fargate
Amazon
API Gateway
Amazon
SNS
Amazon
SQS
COMPUTE
DATA STORES
INTEGRATION
Amazon Aurora
Serverless
Amazon
S3
Amazon
DynamoDB
Amazon
EventBridge
FAAS
AWS
Step Functions
AWS
AppSync

13. Single Responsibility Principle
ü Do’s ✘ Don’ts *
- Input validation
- Business logic /!
- Transform data
- Return result
- Event/Input Filtering
- Transport data
- Orchestration & long
transactions
- Retry/Failure handling
* Most of the time

14. Event Filtering
15
SNS
Topic
Publisher
if event_type == 'order_created’:
lambda_client.invoke('OrderCreation', ...)
elif event_type == 'order_placed’:
lambda_client.invoke('OrderPlacement', ...)
elif event_type == 'order_cancelled’:
lambda_client.invoke('OrderCancelation', ...)
OrderCreation
OrderPlacement
OrderCancellation
{
"event_type": "order_placed",
"order": {
"id": "232134",
"amount": "2341,45",
"stock_ref": "AMZN”
}
}
the wrong way
𝝺 function code
Input event
OrderFiltering

15. Event Filtering with SNS
16
OrderCreation
OrderPlacement
OrderCancellation
Publisher
OrderCreationEvent:
Type: AWS::SNS::Subscription
Properties:
TopicArn: 'arn:aws:sns:eu-central-1:123456789:OrdersTopic’
Protocol: lambda
Endpoint: 'arn:aws:lambda:eu-central-1:123456789:function:OrderCreation’
FilterPolicy:
event_type:
- order_created
SNS
Topic
https://docs.aws.amazon.com/sns/latest/dg/sns-subscription-filter-policies.html
Cloudformation template
{
"event_type": [
"order_created"
]
}
Filter policy

16. Event Filtering with SNS
17
OrderCreation
OrderPlacement
OrderCancellation
Publisher
OrderPlacementEvent:
Type: AWS::SNS::Subscription
Properties:
TopicArn: 'arn:aws:sns:eu-central-1:123456789:OrdersTopic’
Protocol: lambda
Endpoint: 'arn:aws:lambda:eu-central-1:123456789:function:OrderPlacement’
FilterPolicy:
event_type:
- order_placed
SNS
Topic
Cloudformation template

17. Event Filtering with SNS
18
OrderCreation
OrderPlacement
OrderCancellation
Publisher
OrderCancellationEvent:
Type: AWS::SNS::Subscription
Properties:
TopicArn: 'arn:aws:sns:eu-central-1:123456789:OrdersTopic’
Protocol: lambda
Endpoint: 'arn:aws:lambda:eu-central-1:123456789:function:OrderCancellation’
FilterPolicy:
event_type:
- order_cancelled
SNS
Topic
Cloudformation template

18. Event Filtering with EventBridge
19
https://aws.amazon.com/blogs/compute/reducing-custom-code-by-using-advanced-rules-in-amazon-eventbridge/
{
"Source": "custom.myATMapp",
"EventBusName": "default",
"DetailType": "transaction",
"Time": "Wed Jan 29 2020 08:03:18 GMT-0500",
"Detail":{
"action": "withdrawal",
"location": "NY-NYC-001",
"amount": 300,
"result": "approved",
"transactionId": "123456",
"cardPresent": true,
"partnerBank": "Example Bank",
"remainingFunds": 722.34
}
}
{
"source": [ "custom.myATMapp" ],
"detail-type": [ "transaction" ],
"detail": {
"amount": [ { "numeric": [ ">", 300 ] } ]
}
}
{
"source": [ "custom.myATMapp" ],
"detail-type": [ "transaction" ],
"detail": {
"location": [ { "prefix": "NY-NYC-" } ]
}
}
{
"source": [ "custom.myATMapp" ],
"detail-type": [ "transaction" ],
"detail": {
"partnerBank": [ { "exists": true } ]
}
}
{
"source": [ "custom.myATMapp" ],
"detail-type": [ "transaction" ],
"detail": {
"result": [ "approved" ],
"partnerBank": [ { "exists": false } ],
"location": [ { "anything-but": "NY-NYC-002" }]
}
}

19. Orchestration
20
the wrong way
invoke
invokeif (…
)
invoke //
else
if (success)
Notify with SNS
n * invoke
if (failure)
Enqueue error
notify with SNS
need approval
App…

20. Simple orchestration with Lambda destinations
21
invoke
invokeif (…
)
invoke //
else
if (success)
Notify with SNS
n * invoke
if (failure)
Enqueue error
notify with SNS
need approval
App…
Lambda Destinations

21. Simple orchestration with Lambda destinations
22
Amazon SNS
Amazon
EventBridge
Amazon
Cloudwatch Logs
Amazon S3
Amazon SES
AWS Config
Amazon
CloudFormation
AWS
CodeCommit
A
S
Y
N
C
"DestinationConfig": {
"onSuccess": {
"Destination": "arn:aws:lambda:..."
},
"onFailure": {
"Destination": "arn:aws:sqs:..."
}
}
Cloudformation template
Amazon SNS
Amazon
EventBridge
Amazon
SQS
AWS Lambda
if success:
return {...}
else:
raise Exception(‘Failure', {...})
𝝺 function code
Lambda function
A
S
Y
N
C

22. Advanced orchestration with Step Functions
23
invoke
invokeif (…
)
invoke //
else
if (success)
Notify with SNS
n * invoke
if (failure)
Enqueue error
notify with SNS
need approval
App…

23. Advanced orchestration with Step Functions
24
invoke
invokeif (…
)
invoke //
else
if (success)
Notify with SNS
n * invoke
if (failure)
Enqueue error
notify with SNS
need approval
App…
{
"StartAt": "SimpleInvocation",
"States": {
"SimpleInvocation": {
"Type": "Task",
"Resource": "arn:aws:lambda:eu-central-
1:123456789012:function:HelloFunction",
"Next": "Choose1or2"
},

24. Advanced orchestration with Step Functions
25
invoke
invokeif (…
)
invoke //
else
if (success)
Notify with SNS
n * invoke
if (failure)
Enqueue error
notify with SNS
need approval
App…
"Choose1or2": {
"Type": "Choice",
"Choices": [
{
"Variable": "$.foo”,
"NumericEquals": 1,
"Next": "Lambda1"
},
{
"Variable": "$.foo",
"NumericEquals": 2,
"Next": "ParallelInvocation"
}
],
"Default": "Unmatched"
},

25. Advanced orchestration with Step Functions
26
invoke
invokeif (…
)
invoke //
else
if (success)
Notify with SNS
n * invoke
if (failure)
Enqueue error
notify with SNS
need approval
App…
"Lambda1": {
"Type": "Task",
"Resource": "arn:aws:lambda:eu-
central-1:123456789012:function:Lambda1",
"Next": "SuccessOrFailure"
},

26. Advanced orchestration with Step Functions
27
invoke
invokeif (…
)
invoke //
else
if (success)
Notify with SNS
n * invoke
if (failure)
Enqueue error
notify with SNS
need approval
App…
"SuccessOrFailure": {
"Type": "Choice",
"Choices": [
{
"Variable": "$.status",
"StringEquals": "SUCCESS",
"Next": "SendNotification"
},
{
"Variable": "$.status",
"StringEquals": "FAILURE",
"Next": "QueueError"
}
],
"Default": "Unmatched"
}

27. Advanced orchestration with Step Functions
28
invoke
invokeif (…
)
invoke //
else
if (success)
Notify with SNS
n * invoke
if (failure)
Enqueue error
notify with SNS
need approval
App…
"SendNotification": {
"Type": "Succeed"
},
"QueueError": {
"Type": "Fail"
},

28. Advanced orchestration with Step Functions
29
invoke
invokeif (…
)
invoke //
else
if (success)
Notify with SNS
n * invoke
if (failure)
Enqueue error
notify with SNS
need approval
App…
"ParallelInvocation": {
"Type": "Parallel",
"Branches": [
{
"StartAt": "SendApprovalRequest",
"States": {
"SendApprovalRequest": {
// ...
}
},
{
"StartAt": "Loop",
"States": {
"Loop": {
// ...
}
}
}

29. Advanced orchestration with Step Functions
30
invoke
invokeif (…
)
invoke //
else
if (success)
Notify with SNS
n * invoke
if (failure)
Enqueue error
notify with SNS
need approval
App…
"SendApprovalRequest": {
"Type": "Task",
"Resource":
"arn:aws:states:::lambda:invoke.waitForTaskToken",
"Parameters": {
"FunctionName": "sendMailForApprovalFunction",
"Payload": {
"step.$": "$$.State.Name",
"model.$": "$.data",
"token.$": "$$.Task.Token"
}
},
"ResultPath": "$.output",
"Next": "Approved",
"Catch": [
{
"ErrorEquals": [ "rejected" ],
"ResultPath": "$.reason",
"Next": "Rejected"
}
]
}
SendTaskSuccess
SendTaskFailure

30. Advanced orchestration with Step Functions
31
invoke
invokeif (…
)
invoke //
else
if (success)
Notify with SNS
n * invoke
if (failure)
Enqueue error
notify with SNS
need approval
App…
"Loop": {
"Type": "Map",
"ItemsPath": "$.loopItems",
"Iterator": {
"StartAt": "LoopLambda",
"States": {
"LoopLambda": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-
1:123456789012:function:LoopFunction",
"End": true
}
}
},
"End": true
}

31. Advanced orchestration with Step Functions
32
invoke
invokeif (…
)
invoke //
else
if (success)
Notify with SNS
n * invoke
if (failure)
Enqueue error
notify with SNS
need approval
App…

32. TL;DR Single Responsibility Principle
33
èKeep your 𝝺 code focused on the business
This is not the responsibility of a 𝝺 to do orchestration

33. You ain’t gonna need it
34
Welcome in the “functionless” world !

34. API Gateway Service Proxy
35

35. Ex: insert data in DynamoDB
36
Resource: /comments
HTTP Method: POST
HTTP Request Body: {
"pageId": "example-page-id",
"userName": "ExampleUserName",
"message": "Example comment to be added."
}
Table: Comments
commentId: String
userName: String
message: String
pageId: String
PK: commentIdAPI Gateway DynamoDBLambda
var AWS = require('aws-sdk');
var ddb = new AWS.DynamoDB({apiVersion: '2012-08-10'});
exports.handler = async function(event, context) {
var params = {
TableName: 'Comments’,
Item: {
'commentId' : {
S: 'randomid’
},
'pageId' : {
S: event.pageId
},
'userName' : {
S: event.userName
},
'message' : {
S: event.message
}
}
};
ddb.putItem(params, function(err, data) {
if (err) {
console.log("Error", err);
} else {
console.log("Success", data);
}
});
}

36. Ex: insert data in DynamoDB
37
Resource: /comments
HTTP Method: POST
HTTP Request Body: {
"pageId": "example-page-id",
"userName": "ExampleUserName",
"message": "Example comment to be added."
}
Table: Comments
commentId: String
userName: String
message: String
pageId: String
PK: commentIdAPI Gateway DynamoDB

37. Ex: insert data in DynamoDB
38
Resource: /comments
HTTP Method: POST
HTTP Request Body: {
"pageId": "example-page-id",
"userName": "ExampleUserName",
"message": "Example comment to be added."
}
Table: Comments
commentId: String
userName: String
message: String
pageId: String
PK: commentIdAPI Gateway DynamoDB

38. Ex: insert data in DynamoDB
39
Resource: /comments
HTTP Method: POST
HTTP Request Body: {
"pageId": "example-page-id",
"userName": "ExampleUserName",
"message": "Example comment to be added."
}
Table: Comments
commentId: String
userName: String
message: String
pageId: String
PK: commentIdAPI Gateway DynamoDB

39. Ex: insert data in DynamoDB
40
Resource: /comments
HTTP Method: POST
HTTP Request Body: {
"pageId": "example-page-id",
"userName": "ExampleUserName",
"message": "Example comment to be added."
}
Table: Comments
commentId: String
userName: String
message: String
pageId: String
PK: commentIdAPI Gateway DynamoDB

40. Ex: insert data in DynamoDB
41
Resource: /comments
HTTP Method: POST
HTTP Request Body: {
"pageId": "example-page-id",
"userName": "ExampleUserName",
"message": "Example comment to be added."
}
Table: Comments
commentId: String
userName: String
message: String
pageId: String
PK: commentIdAPI Gateway DynamoDB

41. Use with caution
42
• Not a generic design pattern, not
always applicable
• Apply when the lambda is a
passthrough (no business code, just
mapping)
• Mapping can sometimes be complex
(Velocity Template Language)

42. Step Function integrations
43
"QueueError": {
"Type": "Task",
"Resource": "arn:aws:states:::sqs:sendMessage",
"Parameters": {
"QueueUrl": "https://sqs.eu-central-1.amazonaws.com/123456789012/myQueue",
"MessageBody.$": "$.input.message"
},
"End": true
},
"SendNotification": {
"Type": "Task",
"Resource": "arn:aws:states:::sns:publish",
"Parameters": {
"TopicARN": "arn:aws:sns:eu-central-
1:123456789012:myTopic",
"Subject": "Lambda1 has successfully finish its job",
"Message.$" : "$.input.message"
},
"End": true
},
SQS
SNS

43. Step Function integrations
44
AWS Batch Amazon DynamoDB Amazon ECS / Fargate Amazon EMR AWS Glue
Amazon SageMaker Amazon SNS Amazon SQS AWS Step Functions
AWS Lambda
AWS CodeBuild

44. TL;DR You Ain’t Gonna Need It
45
è 𝝺 is not always needed
You can save costs and
optimize performance
when functions are just passthrough/mapping

45. Keep it simple stupid
46
Lighten your functions

46. Keep your functions simple & stupid
nano functions
API GW
/res1
/res2
/res3
= 1 handler (1 function)
= 1 file
Not that stupid
so they need
sisters to do the job !

47. Keep your functions simple & stupid
nano functions
API GW
/res1
/res2
/res3
= 1 handler (1 function)
= 1 file
function-lith
API GW
/{proxy}
/res1
/res2
/res3
That’s really not simple & stupid!
= 1 handler (1 function)
= 1 file

48. Keep your functions simple & stupid
nano functions
API GW
/res1
/res2
/res3
function-lith
API GW
/{proxy}
/res1
/res2
/res3
= 1 handler (1 function)
= 1 file
fat functions
API GW
/res1
/res2
/res3
= 3 handlers (3 functions)
= 1 file
= 1 handler (1 function)
= 1 file

49. Keep your functions simple & stupid
50
nano functions
API GW
/res1
/res2
/res3
function-lith
API GW
/{proxy}
/res1
/res2
/res3
fat functions
= 1 handler (1 function)
= 1 file
API GW
= 3 handler (3 functions)
= 1 file
micro functions
API GW
/res1
/res2
/res3
/res1
/res2
/res3
= 1 handler (1 function)
= 1 file
= 1 handler (1 function)
= 1 file

50. Keep your functions simple & stupid
https://github.com/cdk-patterns/serverless/tree/master/the-lambda-trilogy
Potential duplicated code ++
Cognitive burden ++
Coupled functions
Coupled deployments
nano functions
API GW
/res1
/res2
/res3
function-lith
API GW
/{proxy}
/res1
/res2
/res3
fat functions
= 1 handler (1 function)
= 1 file
API GW
= 3 handler (3 functions)
= 1 file
micro functions
/res1
/res2
/res3
= 1 handler (1 function)
= 1 file
API GW
/res1
/res2
/res3
= 1 handler (1 function)
= 1 file
Stupidity Complexity
FAAS?
Longer cold starts ++
Risk of blast radius
Framework dependent
Longer cold starts
Risk of blast radius
Potential duplicated code
Cognitive burden

51. TL;DR Keep it simple stupid
52
Lighter functions
=
Easier to test and maintain
Faster to start: less cold start
More scalable: higher throughput
More secure: less permission needed

52. Conclusion
No function is easier to manage
than ‘no function’
– me
è If you can do better without a
function, just do it
è Else, apply software
craftsmanship principles
(clean code, tests, code reviews…)
“No server is easier to
manage than ‘no server’”
– Werner Vogels

53. Thank You @jeromevdl
https://tinyurl.com/ydeowzut
2-minutes survey:

54. Appendix

55. AWSTemplateFormatVersion: 2010-09-09
Resources:
API:
Type: AWS::ApiGateway::RestApi
Properties:
Name: !Sub ${AWS::StackName}-api-
${AWS::AccountId}
APIDeployment:
Type: AWS::ApiGateway::Deployment
Properties:
RestApiId: !Ref API
StageName: prod
DependsOn:
- ListBucketAPI
APIBucketResource:
Type: AWS::ApiGateway::Resource
Properties:
ParentId: !GetAtt API.RootResourceId
PathPart: "{bucket}"
RestApiId: !Ref API
ListBucketAPI:
Type: AWS::ApiGateway::Method
Properties:
HttpMethod: GET
ResourceId: !Ref APIBucketResource
RestApiId: !Ref API
AuthorizationType: NONE
Integration:
Credentials: 'arn:aws:iam::1234567890:role/role-demo-api-gw-s3-integration’
IntegrationHttpMethod: GET
IntegrationResponses:
- StatusCode: "200"
PassthroughBehavior: WHEN_NO_MATCH
RequestParameters:
integration.request.header.Content-Type: method.request.header.Content-Type
integration.request.header.x-amz-acl: "'authenticated-read’”
integration.request.path.bucket: method.request.path.bucket
Type: AWS
Uri: !Sub arn:aws:apigateway:${AWS::Region}:s3:path/{bucket}
MethodResponses:
- StatusCode: "200"
RequestParameters:
method.request.path.bucket: true
method.request.header.Content-Type: false
API Gateway & S3 sample
https://docs.aws.amazon.com/apigateway/latest/developerguide/integrating-api-with-aws-services-s3.html

56. 57
Advanced orchestration with Step Functions{
"StartAt": "SimpleInvocation",
"States": {
"SimpleInvocation": {
"Type": "Task",
"Resource": "arn:aws:lambda:eu-central-1:123456789012:function:HelloFunction",
"Next": "Choose1or2"
},
"Choose1or2": {
"Type": "Choice",
"Choices": [
{
"Variable": "$.foo",
"NumericEquals": 1,
"Next": "Lambda1"
},
{
"Variable": "$.foo",
"NumericEquals": 2,
"Next": "ParallelInvocation"
}
],
"Default": "Unmatched"
},
"Lambda1": {
"Type": "Task",
"Resource": "arn:aws:lambda:eu-central-1:123456789012:function:Lambda1",
"Next": "SuccessOrFailure"
},
"SuccessOrFailure": {
"Type": "Choice",
"Choices": [
{
"Variable": "$.status",
"StringEquals": "SUCCESS",
"Next": "SendNotification"
},
{
"Variable": "$.status",
"StringEquals": "FAILURE",
"Next": "QueueError"
}
],
"Default": "Unmatched"
},
"SendNotification": {
"Type": "Succeed"
},
"QueueError": {
"Type": "Fail"
},
"ParallelInvocation": {
"Type": "Parallel",
"Branches": [
{
"StartAt": "SendApprovalRequest",
"States": {
"SendApprovalRequest": {
"Type": "Task",
"Resource": "arn:aws:states:::lambda:invoke.waitForTaskToken",
"Parameters": {
"FunctionName": "sendMailForApprovalFunction",
"Payload": {
"step.$": "$$.State.Name",
"model.$": "$.data",
"token.$": "$$.Task.Token"
}
},
"ResultPath": "$.output",
"Next": "Approved",
"Catch": [
{
"ErrorEquals": [ "rejected" ],
"ResultPath": "$.reason",
"Next": "Rejected"
}
]
},
"Approved": {
"Type": "Task",
"Resource": "arn:aws:lambda:eu-central-1:123456789012:function:Lambda1",
"End": true
},
"Rejected": {
"Type": "Fail"
}
}
},
{
"StartAt": "Loop",
"States": {
"Loop": {
"Type": "Map",
"ItemsPath": "$.loopItems",
"Iterator": {
"StartAt": "LoopLambda",
"States": {
"LoopLambda": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:123456789012:function:LoopFunction",
"End": true
}
}
},
"End": true
}
}
}
],
"End": true
},
"Unmatched": {
"Type": "Fail",
"Error": "DefaultStateError",
"Cause": "No Matches!"
}
}
}