You want to migrate your existing application to serverless and you don’t know where to start. This is a common problem that a lot of the architects, CTOs and developers have, as it is very rare that we start a project from a Greenfield. In this talk, I will walk you through different strategies to migrate an existing application to serverless. We will look at known architectures existing challenges in applications and how we can overcome them with serverless. And also I will share what I learnt when I worked on the migration of one existing microservices application into serverless. Track: DevOps: Culture of working together and the technology that makes it happen

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How to migrate an existing
application to serverless
Marcia Villalba
@mavi888uy

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About me
AWS Developer Advocate
Coding for more than 15 years
Host of FooBar YouTube Channel
https://youtube.com/foobar_codes

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Serverless
”Serverless is a
methodology for
planning, building and
deploying software in a
way that maximizes value
by minimizing
undifferentiated heavy
lifting…”
Jeremy Daly

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What it means that something is serverless?
No managing infrastructure High availability built in
Pay for what you useScales automagically

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Function as a Service (FaaS)
“AWS Lambda lets you run code without
provisioning or managing servers. ...
…Just upload your code and Lambda takes care
of everything required to run and scale your code
with high availability.
You can set up your code to automatically
trigger from other AWS services or call it directly
from any web or mobile app”
AWS – Lambda definition
AWS
Lambda

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How AWS Lambda works?
Event source Function Services
Node.js
Python
Java
C#
Go
Custom runtimes
Changes in
data state
Requests to
endpoints
Changes in
resource state
Amazon S3
DynamoDB
Amazon
SQS

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Managed services
Amazon S3
Amazon SQS
DynamoDB

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Managing unknowns

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Lack of technology knowledge

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Will this solve my problem?

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Foundational work

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Conway Law
”Any organization that designs a system will inevitably
produce a design whose structure is a copy of the
organization communication structure…”
Melvin Conway
Reverse Conway’s maneuver
Structure your organization to match the software you
would like to build
Small, agile teams – Two pizza teams

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Pick your tools
- Programming languages
- Deployment frameworks
- Developer tools

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Use Infrastructure as code
1. Minimize risk and bugs
2. Make infrastructure changes
repeatable and predictable
3. infrastructure changes using the
same tools as code changes

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CI/CD

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Monitoring and observability
Make sure that all your services send
metrics and logs
Pick a centralized tool for handling this

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Migration strategies
The real fun part 😅

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The big rewrite
Please don’t do it
Strategy 1

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Strategy 2 - The monolithic function
Move your existing monolith with the least amount of changes to a big
function.
If you application is too big, move it to AWS Fargate – Serverless containers

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Strategy 2 - The monolithic function
Good option if you want to migrate from an on-prem to the cloud
Combined with the next pattern it can be the first step
Some tools to help you out:
• For NodeJS:
- Serverless express (https://serverless.com/plugins/serverless-express/)
- Serverless HTTP (https://github.com/dougmoscrop/serverless-http)
• For Java
- Serverless Java Container (https://github.com/awslabs/aws-serverless-java-
container)

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Strategy 3 - Strangler pattern
Monolith
Users
DB
Monolith
Service1
LB
Users
DBDB
Monolith
LB
Service1 Service n
Users
DB DB DB

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The strangler pattern

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Steps for doing the strangler pattern
Migrating to serverless in 5 steps

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Big mess of Customer, orders and inventory business logic
OrderId Order info
CustomerId Customer
info…
CustomerId OrderId OrderId ItemId
ItemId Item info
DB manager
Authentication / User management

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Step 1 – Find the seams in the code
”… a seam is a portion of the code that can be treated
in isolation and worked on without impacting the rest
of the codebase…”
Michael Feathers

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Step 1 – Find the bounded context in the code
Examples of seams in Java
Package content
- Organize your code inside different packages if its not done already
Example of seams in Javascript
Modules
- Be careful when moving things around if you don’t have unit tests.

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ItemsCustomersOrders
OrderId Order info
CustomerId Customer
info…
CustomerId OrderId OrderId ItemId
ItemId Item info
DB manager
Authentication / User management

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Package1
Repository1
Package2
Repository2
PackageN
Repository
N
Monolithic application
DB
Step 2 – Organizing the data

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ItemsCustomers Orders
OrderId Order info
CustomerId Customer
info…
CustomerId OrderId
OrderId ItemId
ItemId Item info
DB order manager
DB customer
manager
DB items manager
Authentication / User management

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Step 3 – Move the code gracefully
1. Choose what to
migrate first
2. Rebuild it as a
serverless component
Tidy
Monolith
Users
DB
Tidy
Monolith
Service1
LB
Users
DBDB

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Where to start?
Strategy 1
Start with the least critical
part of your system
Strategy 2
Start with the part of the
system with the highest
return of invested time
🤔

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My strategy
Start with the least critical
part of your system (2 or 3
services)
Then move the most
critical part

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Some things to rethink when
moving to serverless

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Tidy Monolith
LB
Users
Logical microservice
AWS Lambda AWS Lambda
AWS Lambda AWS Lambda
AWS Lambda
DB
DB

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Evolutionary architecture
- Modularity and decoupling
- Organized around business capabilities
- Experimentation
Rebecca Parsons and Neal Ford

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Single responsibility principle
“A class should have only one reason to change”
Robert C. Martin – Uncle Bob
In the serverless worlds this means:
- Simpler functions – easier to know what they are doing
- Less code to test
- Single purpose functions are more secure
- Single purpose functions perform better

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Orchestration pattern
Process manager will handle all the incoming events
Knows the status of all the processes running
Knows how to make all the services work together

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Get order
detailsGet order
details
Orchestration pattern
Get customer
orders
DB
Eg. Get customer orders
Get order
details
Order service
Generate
results

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Choreography and event driven architectures
Add a customer
Save
customer info
DB
Generate
thumbnail
Update
customer info
with
thumbnail
DBStorage

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Components emit events and other components react to those events
We don’t want components talking to each other as this adds a lot of coupling
Choreography and event driven architectures

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So we need a router

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Why do you need a router?

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Decoupling the services and functions
- Independent releases
- Scalability
- Modular code
- Easy to maintain and to work on
- Adds resiliency to the application Amazon Simple
Notification
Service
Amazon Simple
Queue Service
Amazon
EventBridge

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Replace existing functionality with managed services
Amazon Cognito
Order service
Customer
service
Items service
Users

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Serverless analytics pipeline
Amazon Cognito
Amazon S3 Users
Amazon
Kinesis Data
Firehose
Amazon
Athena
AWS Glue Amazon
QuickSight
S3
Bucket
AWS Cloud
Client

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Step 4 - Breaking the database
Logical microservices should own their data
Migrate the data to the new database
Rethink how your data is stored – noSQL, files, SQL,
ect.

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Step 5 – Breaking the APIs
We need to keep the APIS compatible after migration for our clients
We want to switch the traffic to the new service gradually

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Move traffic gradually to the new service
Tidy Monolith with
old service 1
Service1
Application Load
Balancer
Users
30% traffic
70% traffic
ALB Weighted Target Groups

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Case Study

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SCALING CHALLENGES
350
DONATIONS PER SECOND

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2016
Drupal 7 monolith
- Static content
- Pay-in fundraising
- Gift aid declaration
- Fundraiser gallery
- Contact us
Giving
Pages
Donate

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2017
Drupal 7 monolith
- Static content
- Contact us
Drupal 8
- Static content
Pay-in
fund-
raising
SMS
Gift aid
Fundraise
gallery
Giving
Pages
Donate

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2018
Drupal 8
- Static content
Pay-in fund-
raising
SMS
Gift aid
Giving
Pages
Donate
Contact
us
Red Nose
Comp
School
step calc

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2018
Drupal 8
- Static content
Pay-in fund-
raising
SMS
Gift aid
Contact
usGiving
Pages
Donate
Red Nose
Comp
School
step calc
Mailer Service
Postcode lookup

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2019
Drupal 8
- Static content
Pay-in fund-
raising
Contact
us
Payment Service layer
Image uploader service
Marketing preferences service
Mailer Service
Postcode lookup service
SMS Gift
Aid
Donate

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Donate
bit.ly/cr-donate-blueprint

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OLD VS NEW
March 2019 cost*
$5,393
March 2015 cost*
$83,908
*All hosting costs are paid for through corporate partnerships.
100% of public donations go to the projects we fund.

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WE COULD DO
IT ALL AGAIN TOMORROW
Serverless services cost
$92

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comicrelief.com/donate

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Closing remarks

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Best practices
Automate everything
Decompose for agility
Standardized tools
Infrastructure as code

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Steps start migrating
1 – Do the foundational work
2 – Move your monolith to the cloud if needed
3 – Find the seams for your code
4 – Organize the data layer
5 – Move the code to serverless
6 – Break the database
7 – Break the APIs
8 – Repeat from step 5 until 7 until you are done

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Thank you!
Marcia Villalba
@mavi888uy