All software architectures have to deal with stress. Its simply the way the world works! Stressors come from multiple directions, including changes in the marketplace, business models, and customer demand, as well as infrastructure failures, improper or unexpected inputs, and bugs. As software architects, one of our jobs is to create solutions that meet both business and quality requirements while appropriately handling stress. We typically approach stressors by trying to create solutions that are robust. Robust systems can continue functioning properly in the presence of internal and external challenges, but they also have one or more breaking points. When we pass a robust system's known threshold for a particular type of stress, it will fail. When a system encounters an unknown unknown challenge, it will usually not be robust! Recent years have seen new approaches, including resilient, antifragile, and evolutionary architectures. All of these approaches emphasize the notion of adapting to changing conditions in order to not only survive stress but sometimes to benefit from it. In this presentation, we'll examine the theory and practice behind these architectural approaches.

1. Architectures that Bend but Don’t Break
Matt Stine
Global Field CTO / Chief Architect
@mstine
http://www.mattstine.com

2. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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Who is this guy?
Matt Stine - Global Field CTO / Chief Architect
at Pivotal
18 year Enterprise IT veteran developer / architect
6 years focused on Cloud Native Platforms and
Architecture
Frequent conference circuit speaker
Host of Software Architecture Radio
http://softwarearchitecturerad.io
I wrote a little cloud book…
https://www.oreilly.com/programming/free/
migrating-cloud-native-application-
architectures.csp
2

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What even is
architecture?

4. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/ 3
What even is
architecture?
What does
“bend but not
break”
mean?

5. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/ 3
What even is
architecture?
What does
“bend but not
break”
mean?
What are
software
stressors?

6. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/ 3
What even is
architecture?
What does
“bend but not
break”
mean?
What are
software
stressors?
What
software
qualities do we
want?

7. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/ 3
What even is
architecture?
What does
“bend but not
break”
mean?
What are
software
stressors?
How do we
measure those
qualities?
What
software
qualities do we
want?

8. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/ 3
What even is
architecture?
What does
“bend but not
break”
mean?
What are
software
stressors?
How do we
create those
qualities?
How do we
measure those
qualities?
What
software
qualities do we
want?

9. 4Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
What even is
architecture?

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5
Architecture: decisions that are hard to reverse.
Matt Parker
Software Architecture: the high level shape and
flow of the software that’s independent of the
problem domain, but dependent on the desired
user experience.

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6
Architecture represents the significant
design decisions that shape a system,
where significance is measured by cost of
change.
Simon Brown

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7
Meaningful architecture is a living, vibrant
process of deliberation, design, & decision,
not just documentation.
Grady Booch

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8
The important stuff (whatever that is).
Ralph Johnson

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9
Architecture is the process by which we
make and capture software engineering
decisions that have system-wide impact and
are often expensive to reverse.
Matt’s Definition

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What even is
architecture?
What does
“bend but not
break”
mean?

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What does
“bend but not
break”
mean?

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12
The oak fought the wind and was broken, the willow
bent when it must and survived.
― Robert Jordan, The Fires of Heaven

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13
Bend but
Don’t Break
Defense (2017)
SOURCE: https://www.patspulpit.com/2018/1/6/16855296/new-england-patriots-defense-took-bend-but-dont-break-to-a-new-level-in-2017
■ Yards per Drive:
32nd (i.e. WORST)
■ Points per Drive:
6th

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Break vs. Bend
Break
■ Fragile
Stress → Destruction
■ Robust
Stress → Resistance
14
Bend
■ Resilient
Stress → Adaptation
■ Antifragile
Stress → Innovation

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15
CREDIT: Bilgin Ibryam - https://developers.redhat.com/blog/2016/07/20/from-fragile-to-antifragile-software/

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16
Resilience is the ability of a system to adapt
or keep working when challenges occur.
Resilience
CREDIT: Ines Sombra - https://speakerdeck.com/randommood/full-stack-fest-architectural-patterns-of-resilient-distributed-systems

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Defining Resilience
■ Fault-tolerance
■ Evolvability
■ Scalability
■ Failure isolation
■ Complexity Management
17
CREDIT: Ines Sombra - https://speakerdeck.com/randommood/full-stack-fest-architectural-patterns-of-resilient-distributed-systems

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18

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Immune Systems
19

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Muscular Systems
20

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Ant Swarms
21

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22

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Software That Improves Itself?
23

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Socio-technical Systems
24

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Socio-technical Systems
24
!
" #!
" #
!
" #
!
" #

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What even is
architecture?
What does
“bend but not
break”
mean?
What are
software
stressors?

32. 26Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
What are
software
stressors?

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Russ Miles’ Stressors
■ Innovation
■ System Wildly Successful!
■ System Hardly Used
■ System Failures
■ Emergent Need to Reuse
27

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What even is
architecture?
What does
“bend but not
break”
mean?
What are
software
stressors?
What
software
qualities do we
want?

35. 29Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
What
software
qualities do we
want?

36. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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30
Can we continuously deliver incremental
value to the business through software?
Innovation

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31
Can we deliver systems that are able to
survive and thrive amidst turbulent
conditions in production?
Wild Success / System Failure

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What even is
architecture?
What does
“bend but not
break”
mean?
What are
software
stressors?
How do we
measure those
qualities?
What
software
qualities do we
want?

39. 33Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
How do we
measure those
qualities?

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34
LEAD TIME: how long does it take you to go
from idea to delivered software?
Innovation

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35
CYCLE TIME: how long does it take you to
make a change and deliver it to production?
Innovation

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36
INVERSE LEAD TIME: how long does it take
for feedback to enter your development
queue?
Innovation

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37
TRASH RATIO: how many of your
experiments do you end up discarding?
Innovation

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38
■ Service Level Objectives (SLOs)
■ Steady State Metrics
Resilience

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39

46. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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SRE Measures
■ Service Level Indicator:
Quantitative measure of an aspect of level of service provided (e.g. request
latency)
■ Service Level Objective:
Target value/range of values for a service level measured by an SLI
40

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Focus on Distributions
41
Not on Averages!
https://landing.google.com/sre/book/chapters/service-level-objectives.html

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Four Golden Signals
■ Latency:
Time it takes to service a request.
■ Traffic:
How much demand is placed on the system.
■ Errors:
Rate of requests that fail.
■ Saturation:
How "full" your service is.
42

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Steady State
43
Some externally visible business metric with
a low degree of variation.

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Netflix: SPS
44
Successful Streaming Starts per Second

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Starts Per Second
45
A single indicator that closely approximates our most important activity: viewing.
A single indicator that closely approximates our
most important activity: viewing.

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46
WHAT IS YOUR MOST IMPORTANT ACTIVITY?

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47
WHAT SINGLE INDICATOR COULD YOU USE TO
APPROXIMATE IT?

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The Ultimate Metric
48
TTRTime to Recovery

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What even is
architecture?
What does
“bend but not
break”
mean?
What are
software
stressors?
How do we
create those
qualities?
How do we
measure those
qualities?
What
software
qualities do we
want?

56. 50Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
How do we
create those
qualities?

57. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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51
Can we continuously deliver incremental
value to the business through software?
Innovation

58. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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52

59. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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53
This paper discusses modularization as a
mechanism for improving the flexibility and
comprehensibility of a system while allowing
the shortening of its development time. The
effectiveness of a "modularization” is
dependent upon the criteria used in dividing
the system into modules.

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54
The major progress in the area of modular
programming has been the development of
coding techniques and assemblers which (1)
allow one module to be written with little
knowledge of the code used in another
module and, (2) allow modules to be
reassembled and replaced without
reassembly of the whole system.

61. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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55
Let’s build an online store!
Decomposition Techniques

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56
Product
Catalog
Orders Inventory Payment Fulfillment ShippingNotifications

63. 57
Data
Services
UI

64. 57
Domain Model
Data
Services
UI

65. 57
Domain Model
Data
Services
UI

66. 57
Services
Domain Model
Data
Services
UI

67. 57
Services
Domain Model
Data
Services
UI

68. 57
MVC Controllers / Views
Services
Domain Model
Data
Services
UI

69. 57
MVC Controllers / Views
Services
Domain Model
Data
Services
UI

70. 57
MVC Controllers / Views
Services
Domain Model
Data
Services
UI

71. 57
MVC Controllers / Views
Services
Domain Model
Data
Services
UI

72. Functional Decomposition
Independent
Development
Dependent on shared
data formats and
schema. Must be jointly
defined and agreed
upon across multiple
groups.
Comprehensibility
You need to know
something about how
all of the modules work
to understand the
whole system.
Changes
Struggles with
knowledge spread
across all modules, so
often each module has
to change in response
to a desired functional
change.
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73. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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59
Let’s Refactor to a
Capability Decomposition
Decomposition Techniques

74. 60

75. 60

76. 60

77. 60

78. 60

79. 60

80. 60

81. Capability Decomposition
Independent
Development
Has abstract interfaces
that encapsulate the
work to be done.
Comprehensibility
You can understand
modules
independently.
Changes
Usually isolates a
change to a single
module.
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83. DOMAIN
DRIVEN
DESIGN

84. hexagonal
architecture
DOMAIN
DRIVEN
DESIGN

85. Strategic Design - the View from 35,000 FEET

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64
!
!
!
"
"
"
πελάτης
πελάτης
πελάτης
πελάτης
πελάτης
πελάτης
!
!
!
"
"
"
!
!
!
"
"
"
ग्राहक
ग्राहक
ग्राहक
ग्राहक
ग्राहक
ग्राहक
Bounded
Contexts

87. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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64
!
!
!
"
"
"
πελάτης
πελάτης
πελάτης
πελάτης
πελάτης
πελάτης
!
!
!
"
"
"
!
!
!
"
"
"
ग्राहक
ग्राहक
ग्राहक
ग्राहक
ग्राहक
ग्राहक
Bounded
Contexts

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■ Business Invariants
■ Policies
■ Transactions
■ State
■ Persistence
65
Now it’s time to start speaking the
Ubiquitous Language within each Bounded Context.
Tactical Design?
■ Business Invariants
■ Policies
■ Transactions
■ State
■ Persistence

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The Central Concept
66
Aggregate

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The Central Concept
66
Aggregate
A cluster of objects
treated as a single unit.
Often modeled as a
state machine.
The atomic unit for any
transactional
behavior.
Only accessed through its
Root Entity.
Responsible for maintaining
any/all business invariants.
Entity
EntityEntity
Value
Object
Value
Object
Value
Object

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67
Application Service
Hexagonal
Architecture

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67
Application Service
Domain
Model
Hexagonal
Architecture
■ Domain Model (Aggregates, etc.)
wrapped by an Application Service

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67
Application Service
Domain
Model
Port
Port
Port
Port
Port Port
Hexagonal
Architecture
■ Domain Model (Aggregates, etc.)
wrapped by an Application Service
■ Ports represent generic
entry/exit points (interface)

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67
Application Service
Domain
Model
Adapter
Port
Port
Port
Port
Port Port
Adapter
Adapter
Adapter
Adapter
Hexagonal
Architecture
■ Domain Model (Aggregates, etc.)
wrapped by an Application Service
■ Ports represent generic
entry/exit points (interface)
■ Adapters represent specific
entry/exit implementations (class)

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68
Adapter
Port
Port
Port
Port
Port Port
Adapter
Adapter
Adapter
Adapter
Order
(root)
Line Item
Order ID
Order
Repository
Order Placed
Application Service
Hexagonal
Architecture
■ Domain Model (Aggregates, etc.)
wrapped by an Application Service
■ Ports represent generic
entry/exit points (interface)
■ Adapters represent specific
entry/exit implementations (class)

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Adapter
Port
Port
Port
Port
Port Port
Adapter
Adapter
Adapter
Adapter
Adapter
Adapter
Adapter
Adapter
REST
SOAP
AMQP
AdapterAdapterKafka
JDBC
69
Application Service
Order
(root)
Line Item
Order ID
Order
Repository
Order Placed
Hexagonal
Architecture
■ Domain Model (Aggregates, etc.)
wrapped by an Application Service
■ Ports represent generic
entry/exit points (interface)
■ Adapters represent specific
entry/exit implementations (class)

97. 70
Software
ModuleAggregate
Entity
EntityEntity
Value
Object
Value
Object
Value
Object
≤
!"
ग्राहकग्राहक
Aggregate
Aggregate≤
Aggregate ≤ SizeOf(Module) ≤ Bounded Context
The Golden Rule

98. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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Deployment Topology Spectrum
71
Big
Ball
of
Mud
Monolith Modular Monolith Microservices

99. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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72
■ Individually Deployable
■ Individually Upgradeable
■ Individually Replaceable
■ Individually Scalable
■ Heterogeneous Tech Stacks
Modular Monolith Microservices
■ High Cohesion
■ Low Coupling
■ Business Capability Focus
■ Bounded Contexts / Aggregates
■ Data Encapsulation
■ Substitutable
■ Composable

100. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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73
Can we deliver systems that are able to
survive and thrive amidst turbulent
conditions in production?
Wild Success / System Failure

101. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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74
Leverage Patterns
Resilience

102. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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Timeouts
75

103. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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Retries
76

104. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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Bulkheads
77

105. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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Circuit Breakers
78

106. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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79

107. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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80
Embrace Chaos
Antifragility

108. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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Socio-technical Systems
81
!
" #!
" #
!
" #
!
" #

109. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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82
https://principlesofchaos.org/

110. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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83

111. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Principles of Chaos Engineering
84
■ Build a Hypothesis around Steady State Behavior
■ Vary Real-world Events
■ Run Experiments in Production
■ Automate Experiments to Run Continuously
■ Minimize Blast Radius

112. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Steady State Behavior
85
A business-facing metric with predictable pattern that fluctuates
significantly when system problems are happening.

113. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Vary Real World Events
86
■ Server Crashes
■ Storage Failures
■ Error Responses
■ Increased Latency between Nodes
■ AZ or Region Failures
■ Thundering Herds

114. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Run Experiments in Production
87
■ Difficult to exactly duplicate the
production environment
■ Impossible to exactly duplicate
production traffic patterns

115. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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88
RUNNING EXPERIMENTS MANUALLY IS
UNSUSTAINABLE
Automate Experiments to Run Continuously

116. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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89
CUSTOMER PAIN WILL HAPPEN.
TAKE STEPS TO ENSURE FALLOUT IS
MINIMIZED AND CONTAINED.
Minimize the Blast Radius

117. Unless otherwise indicated, these slides are © 2013-2018 Pivotal Software, Inc. and licensed under a Creative Commons
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90

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What even is
architecture?
What does
“bend but not
break”
mean?
What are
software
stressors?
How do we
create those
qualities?
How do we
measure those
qualities?
What
software
qualities do we
want?

119. > Stay Connected.
Matt Stine
Global Field CTO / Chief Architect
@mstine
http://www.mattstine.com
#springone@s1p
See also these sessions:
Nate Schutta - Thinking Architecturally
Matt Parker - Agile Architecture