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INFODECK
Self-Contained
Systems
I N F O D E C K
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A monolith contains
numerous things inside
of a single system …
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Various Domains
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User interface
Business logic
Persistence
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… as well as a lot of
modules, components,
frameworks and libraries.
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With all these layers in one
place, a monolith tends to
grow.
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With all these layers in one
place, a monolith tends to
grow.
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If you cut a monolithic
system along its very
domains …
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… and wrap every domain
in a separate, replaceable
web application …
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… then that application
can be referred to as a
self-contained system
(SCS).
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On its outside, an SCS is a
decentralized unit that is
communicating with other
systems via RESTful HTTP
or lightweight messaging.
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Therefore self-contained
systems can be individually
developed for different
platforms.
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An SCS contains its own
user interface, specific
business logic and
separate data storage
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The user interface consists
of web technologies that
are composed according to
ROCA principles.
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Besides a web interface a
self-contained system can
provide an optional API.
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The business logic part
only solves problems that
arise in its core domain.
This logic is only shared
with other systems over a
well defined interface.
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The business logic can
consist of microservices to
solve domain specific
problems.
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Every SCS brings its own
data storage and with it
redundant data depending
on the context and
domain.
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These redundancies are
tolerable as long as the
sovereignty of data by its
owning system is not
undermined.
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This enables polyglot
persistence, which means a
database can be chosen to
solve a domain specific
problem rather than to
fulfill a technical urge.
Neo4J Oracle
CouchDB
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Inside of a self-contained
system a bunch of
technical decisions can be
made independently from
other systems, such as
programming language,
frameworks, tooling or
workflow.
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The manageable domain
specific scope enables the
development, operation
and maintenance of an
SCS by a single team.
Team 1
Team 3
Team 2
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Self-contained Systems
should be integrated over
their web interfaces to
minimize coupling to other
systems.
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Therefore simple hyperlinks can be used to
navigate between systems.
System 1 System 2
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A redirection can be used to ensure
navigation works in both directions.
System 1 System 2
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Hyperlinks can also support the
dynamic inclusion of content that is served by
another application into the web interface of a
self-contained system.
System 1 System 2
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To further minimize
coupling
to other systems,
synchronous remote calls
inside the business logic
should be avoided.
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Instead remote API calls
should be handled
asynchronously to reduce
dependencies and prevent
error cascades.
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This implies that –
depending on the desired
rate of updates – the data
model’s consistency
guarantees are relaxed.
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An integrated
system of systems
like this has many benefits.
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Overall resilience is improved through loosely
coupled, replaceable systems.
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Some systems can be individually
scaled to serve varying demands.
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It is not necessary to perform a risky big bang
release to migrate an outdated, monolithic
system into a system of systems.
Version 1
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It is not necessary to perform a risky big bang
release to migrate an outdated, monolithic
system into a system of systems.
Version 2
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Instead a migration can happen in small,
manageable steps which minimize the risk of
failure and lead to an evolutionary modernization
of big and complex systems.
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Instead a migration can happen in small,
manageable steps which minimize the risk of
failure and lead to an evolutionary modernization
of big and complex systems.
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In reality a system of systems consists of
individually developed software and
standard products.
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A product that fits well in a system of systems
can be chosen by the following aspects: It has to
solve a defined set of tasks and provide the same
integration mechanisms that a self-contained
system offers.
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This ensures that products can be replaced safely
by other products once their
lifetime has ended.
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This ensures that products can be replaced safely
by other products once their
lifetime has ended.
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If a product with such integration mechanisms
can not be found, it should at least be possible to
extend that product with uniform interfaces that
integrate well with the rest of the system.
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