This document discusses strategies for transitioning from monolithic applications to microservices. It covers topics like domain-driven design, event storming, identifying core domains, and technical and business heuristics for determining when to use microservices. It also addresses challenges that can arise with too many microservices and discusses alternative approaches like modular monoliths. The implementation section covers sociotechnical architecture approaches and building cloud-native applications.

1. Confidential │ © 2020 VMware, Inc.
Should That Be a
Microservice ?
Journey From Monoliths to
Microservices and Back
Rohit Kelapure @rkela
Principal Solution Architect @ VMware Pivotal Labs
June 2020
rkelapure@vmware.com
https://cloud.rohitkelapure.com

2. Confidential │ © 2020 VMware, Inc.
Agenda
2
Monoliths To Microservices
DDD To The Rescue
Too Many Microservices
Why? What? How?
Technical Heuristics
6 Factors Of Microservices
Business Heuristics
Wardley Maps, Core Domain Patterns
Modular Monoliths
App Continuum, Service Block & Moduliths
Implementation
SocioTechnical Architecture
Cloud Native Applications
Building Patterns

3. 3Confidential │ © 2020 VMware, Inc.
Monoliths To Microservices
DDD To The Rescue

4. Confidential │ ©2020 VMware, Inc. 4
Your application portfolio is a mix of things
CONTAINERS
EVENT-DRIVEN
FUNCTIONS
DATA
MICROSERVICES
Batch
MONOLITHIC
APPLICATIONS
JEE
COTS
MAINFRAME
.NET
ESB

5. Confidential │ © 2020 VMware, Inc.
What We See
• Complex monolithic systems built over many
years as a web of interdependent parts
• Poor developer experience and productivity
• Slow feature delivery and more bugs
• Tactical treatment of symptoms (ex. latency)
and not core problems (ex. design)
• Technology-focused “horizontal” strategies

6. Confidential │ © 2020 VMware, Inc.
Existing Architecture Makes Improvement Very Hard
This in particular is
not unusual,
especially for
“heritage” systems
in regulated
industries
* From Accelerate: State of DevOps 2019
6

7. Microservices
“In short, the microservice architectural style is an approach to developing a single
application as a suite of small services, each running in its own process and
communicating with lightweight mechanisms, often an HTTP resource API.
These services are built around business capabilities and independently
deployable by fully automated deployment machinery. There is a bare minimum of
centralized management of these services, which may be written in different
programming languages and use different data storage technologies.”
-Fowler, Lewis et al
7

8. Confidential │ © 2020 VMware, Inc. 8
Theory of Microservices
Domain Driven Design
Subdomains Represents a single, logical Domain Model
used to break up the business model logically to
understand the problem space.
Bounded Context : Language based semantic
contextual boundary where each component of the
software model has a specific meaning and does specific
things.
Ubiquitous language: The consistent language spoken
by all members of the team within the Bounded Context.
It is necessary to rigorous, stringent, exact and tight.
Entities: Something with continuity and identity.
Aggregates: Mark the scope within which invariants
have to be maintained stored. An Order Aggregate would
represent the Order, Order Items, Shipping Address, etc.
as a single transactional invariant.

9. Confidential │ © 2020 VMware, Inc. 9
Event Storming
CROSS FUNCTIONAL COLLABORATIVE MODELING OF BUSINESS PROCESS
Drive out the the domains, bounded contexts
& services of a system to reveal vertical slices,
trouble spots & starting points for
rearchitecting it
Make sense of a Huge mess
Making Sure We’re doing the right thing
Enables Cross Perspective Communication
Force Function for CLARITY
Reveals Bounded Contexts, Microservices,
Vertical Slices, Trouble Spots, Starting Points

10. Confidential │ © 2020 VMware, Inc.
Event Storming
Get the right
people in a room
with stickies and a
pen
Use stickies to roughly
define the logical flow
of a system or process Talk it through!
Discover underlying
risks and opportunities
Discover the business flow
and find ideas on where to
start - in a few hours 10
@ziobrando

11. Confidential │ © 2020 VMware, Inc. 11
DDD IS BROKEN
https://cloud.rohitkelapure.com/2019/10/ddd-is-broken.html

12. Confidential │ © 2020 VMware, Inc. 12
Identifying how the system “wants to be behave” @swiftbird68 https://www.swiftbird.us/
The Swift Method
APIs Data
Pub
/Sub
Stories UI/Ext
Domains, Pains,
BehaviorEvent Storm
Boris Model of Notional
Architecture, Mappings,
Direction
Snap-E In parallel with Boris -
API, Data, Pub/Sub
Patterns Technology and Patterns
to Implement
Backlog
The actual work that
needs to be done

13. Confidential │ © 2020 VMware, Inc. 13
Are Your Boundaries (BOUNDED CONTEXTS) Correct ?

14. Boris Exercise
Uses graph theory to model relationships
between the capabilities in a system
● Depends on live collaboration, a lot of
sticky notes and working space
● Uses Event Storming to start an exercise
that identifies system relationships
● Avoids premature solutioning
● Quickly models future system design
● As the diagram is built the team documents
findings
Service
Topic /
Queue
External
System
Async Sync
SAMPLE BORIS DIAGRAM
Confidential │ © 2020 VMware, Inc. 14

15. SNAP
Quickly document Boris outcomes in real-time.
Usually captured using poster-sized sticky paper
on a conference room wall, with one SNAP per
node or service depicted on Boris.
● APIs
● Data
● Pub/Sub
● External Systems/UI
● Agile Stories
● Risks
Sample SNAP
Confidential │ © 2020 VMware, Inc. 15

16. Confidential │ © 2020 VMware, Inc.
Incremental Modernization - Event Thinking
Reduce temporal coupling
● Instrument Monolith with Events
● Break Things apart with events
● Use domain language for events
● Build things on the outside
● Strangler Pattern
● Minimally Invasive
● Cannot rely on ordering of messages or
zero message loss
Strive for autonomy with messaging
● Messaging schemas can introduce
coupling
● Sagas handle Eventual Consistency
● What operations are idempotent ?
● Handle duplicate messages with Outbox
pattern
● Messaging schemas can introduce
coupling
● Avoid Kafka as an ESB anti-pattern
16

17. Confidential │ © 2020 VMware, Inc.
Many Meanings of Event Driven Architecture (EDA)
Event Carried State Transfer
● Update clients in a way that they
don't need to contact the source
system
● Receiver has to maintaining all
the state
● Decoupling
● Reduced load on supplier
● Replicated Data
● Eventual Consistency
Event Sourcing
● Every state change of the system
is recorded as an event
● Event store becomes the source
of truth, and the system state is
derived from it
● Audit, Debugging, Historic State,
Alternative State, Memory Image
● Unfamiliar, External Systems,
Event Schema, Identifiers,
Asynchrony, Versioning
Event Notification
● Send event messages to notify
other systems of a change in its
domain
● Event carries ID and link back to
the sender for more info
● Decouples sender from receiver
● No Statement of overall behavior
Martin Fowler: https://www.youtube.com/watch?v=STKCRSUsyP0
17

18. Confidential │ © 2020 VMware, Inc.
Lessons Learned From Real World Modernizations
Balancing bounded context granularity can be challenging.
Powerpoint is dead, long live the Stickies
Choose the right style of Event Driven Architecture
Correlation strategy and Lock Strategy get complicated.
Complex work-flows require Sagas & Process Managers.
Aggregate <= sizeof(Microservice) <= Bounded Context
DIY Event Sourcing systems are hard. Too much time spent in toil.
Leverage Consumer driven Contracts to establish cschemas across
Bounded Contexts for messages
Delay making frameworks
● Event Sourcing is hard
without a supporting event
persistence framework or
library
● Pick a framework based on
the guidance before
beginning
● Challenge preconceived
architectural decisions
● Set goals with measurable
metrics.
● Be wary of the Hourglass
effect
18

19. Confidential │ © 2020 VMware, Inc.
Too Many Microservices
Why? What? How?
19

20. Confidential │ © 2020 VMware, Inc. 20
Microservices has now
become DEFAULT
Cloud Native and Serverless
have become buzz words
Towards A New Serverless
World
https://www.swiftbird.us/post/towards-a-new-ser
verless-world
Education & Enablement
Should That Be A
Microservices Workshop
Modular Monoliths / App
Continuum
https://www.infoq.com/news/2020/04/microservi
ces-back-again/
Microservices Sprawl -
Leads to POOR
Development & Testing
experience
Poor definition and
understanding of service &
Context Boundaries
Challenges with
Observability and
Heisenbugs
To Microservices and Back Again
Why Go Back to a Monolith ?
HOW? WHY ? WHAT?

21. 21Confidential │ © 2020 VMware, Inc.
Technical Heuristics
Should that be a Microservice? Keep These
Factors in Mind
Please Microservice Responsibly

22. Confidential │ © 2020 VMware, Inc. 22
Technical Heuristics
Multiple Rates Of
Change
Value Streams
Independent Life
Cycles
Speed Matters
Independent
Scalability
Efficiently allocate

23. Confidential │ © 2020 VMware, Inc. 23
Technical Heuristics
Simplify
Interactions with
External
Dependencies
Facades, ACL
Isolated Failure
Failure Domains
Freedom to
Choose the Right
Tech
Polyglot

24. Confidential │ © 2020 VMware, Inc. 24
Microservices - Is the Price Right Workshop ?

25. 25Confidential │ © 2020 VMware, Inc.
Business Heuristics
Wardley Maps To The Rescue

26. Confidential │ © 2020 VMware, Inc. 26
Core Domain -An area of the domain with the
opportunity for high business differentiation. This
represents a compelling ROI. Implementation
must has at-least a reasonable level of model
complexity.
Supporting Domains are business necessities,
they contain business concepts related to the
domain, but there is limited ROI.
Generic Domains represent concepts not-unique
to our domain, such as user identity, sending
emails, taking payments — we should consider
buying SaaS or using open source instead of
building Generic Domains.
Business Heuristics
Context Distillation Invented by Nick Tune @ntcoding

27. Confidential │ © 2020 VMware, Inc. 27
Where is my Core Domain ?

28. Confidential │ © 2020 VMware, Inc. 28
Understand the Business Capability Value Chain Of Your Product
Identify Patterns of Genesis, Product, Utility and Commodity

29. Confidential │ © 2020 VMware, Inc. 29
What are Wardley Maps? Using Miro for Wardley Mapping
Wardley Maps

30. 30Confidential │ © 2020 VMware, Inc.
Simon Brown
“If you can't build a monolith,
what makes you think
microservices are the
answer?”
http://www.codingthearchitecture.com
/2014/07/06/distributed_big_balls_of_m
ud.html Martin Fowler - Monoliths First

31. Confidential │ © 2020 VMware, Inc. 31
Sometimes The Right Answer is a Modular Monolith

32. Confidential │ © 2020 VMware, Inc. 32

33. Confidential │ © 2020 VMware, Inc. 33
Moduliths: A playground to build technology supporting
the development of modular monolithic (modulithic)
Java applications. Repo
Service blocks are cloud-native applications that share
many characteristics with microservices. The key
difference with microservices is that a service block is a
self-contained system that has multiple independently
deployable units—mixing together serverless functions
with containers.
App Continuum: Evolution of a distributed system
starting from a single application and evolving into
several applications and services. Link
Options - Idiomatic Approaches to Modular Monoliths
Moduliths , Service Blocks & App Continuum

34. 34Confidential │ © 2020 VMware, Inc.
Implementation
Sociotechnical Architecture

35. Confidential │ © 2020 VMware, Inc. 35
Team Topologies - Flow Based Teams
Interaction Modes for the Four Fundamental Team Topologies - Skelton & Pais
35

36. Confidential │ © 2020 VMware, Inc. 36
Coupled - End To End Stream Teams
Drawbacks:
● Teams must understand how
to operate in multiple
domains
● Teams can’t confidently
make changes to shared
codebases without
committee approval
● Cross-functional apps don’t
have clear owners to
improve them
● Adding a new team requires
everyone to take on
additional context (the full
ecosystem of domains)
Teams Are Too Coupled During Development

37. Confidential │ © 2020 VMware, Inc. 37
Component Based Teams
Improving Team Independence
Impact:
● Teams can confidently make
changes to and release! code
they own at any time
● Cross-functional apps have
owners to drive improvements
● There’s a clear path to scaling
teams horizontally without
drastic scope change for
existing teams
● Communication between
teams happens between
well-defined public contracts
instead of in-the-weeds
implementation detail

38. Confidential │ © 2020 VMware, Inc.
Building Patterns
Cloud Native
Applications

39. Confidential │ © 2020 VMware, Inc.
A Paved Path To Cloud Native
start.spring.io Gaurdrails
● Spring Cloud Contracts
● Reference Extensible Pipelines
● Security Scanning - Libraries & Code
● Performance Latency Budget Checks
● ArchUnit - Dependency Check
● ErrorProne/Checkstyle - Static Analysis
● CI separate from CD
● Feature Flags
● Coexistance of multiple versions
● Observability - Distributed Traces, Metrics &
Structured Logging
● 15 Factor compliance (API, State, Startup,
External Services)
● Data & App Resiliency safegaurds
39

40. Confidential │ © 2020 VMware, Inc. 40
What Role Do Containers Play ?
Rerence Architecture - @asaikali

41. Confidential │ © 2020 VMware, Inc. 41
Big Picture Overview
Micro Frontends
Each vertically
arranged teams
produces features
in the form of
pages or
fragments.
Use techniques
like SSI or Web
Components to
integrate then
into an
assembled page
https://www.manning.
com/books/micro-fron
tends-in-action

42. Confidential │ © 2020 VMware, Inc. 42
https://cloud.rohitkelapure.com/2018/11/decomposing-ui.html

43. 43Confidential │ © 2020 VMware, Inc.
Conclusion
What Next ?

44. Confidential │ © 2020 VMware, Inc.
Technical + Business + Social Heuristics
Bringing It All Together
44

45. Thank You
Confidential │ © 2020 VMware, Inc.