1. Software Architecture in Practice
Micro Services

2. Henrik Bærbak Christensen
Software Reuse
If only we could build software from reusable components
A big struggle throughout the history of computing
Henrik Bærbak Christensen

3. Software Reuse Vendor Lock-in
During the early 90’ies the Lego bricks metaphor was often used for object/component reuse
However, the golden future of a world wide component market place sort of deflated
Vendor Lock-in
If the kids want to build a large model, adding non-lego bricks does not help! It is basically a vendor lock-in!
Clemens Szyperski (2002). Component Software: Beyond Object-Oriented Programming.

4. Henrik Bærbak Christensen
SideBar
Szyperski predicted a large market
Companies eager to buy reusable components
Suppliers building high-quality reusable components
We never saw it…
Or did we???
Mvnrepository.com is a nice example of component reuse; however it is an open source trading place!
Henrik Bærbak Christensen

5. Henrik Bærbak Christensen
Software Reuse
In the 00’ the web exploded and allowed a different deployment model
Component based reuse:
A static / module viewpoint - get a DLL/jar file
“libraries” in [Lewis et al. 2014]
Linked in, and called by in-memory function calls
Service oriented architecture:
A dynamic / C&C viewpoint - connect to a service
“services” in [Lewis et al. 2014]
Out-of-process, communicate using RPC or web service
Henrik Bærbak Christensen

6. Henrik Bærbak Christensen
Software Reuse
Big difference from the business perspective
Example: A Danish-English dictionary
Consider
Intellectual property rights? ‘Who has the dictionary’?
Updating with new words?
Revenue model?
What are pros/cons of each model: static/dynamic?
Henrik Bærbak Christensen

7. Henrik Bærbak Christensen
SOA
Wikipedia
A service-oriented architecture (SOA) is an architectural pattern in computer software design in which application components provide services to other components via a communications protocol, typically over a network. The principles of service-orientation are independent of any vendor, product or technology.
MacKenzie et al., 2006
is a paradigm for organizing and utilizing distributed capabilities that may be under the control of different ownership domains
provides a uniform means to offer, discover, interact with and use capabilities to produce desired effects consistent with measurable preconditions and expectations
Henrik Bærbak Christensen

8. Web Services
A software system designed to support interoperable machine-to-machine interaction over a network
It has an interface described in a machine-processable format (specifically WSDL)
Other systems interact with the Web service in a manner prescribed by its description using SOAP messages
These are typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards
[W3C, 2004]

9. Key Elements SOAP (Simple Object Access Protocol)
Communication protocol for web services
Typically over HTTP or SMTP
WSDL (Web Service Description Language)
An XML-based language for describing network services
An Interface Description Language for Web services
UDDI (Universal Description, Discovery, and Integration)
Provides a registration and lookup mechanism for clients and servers to find each other
Uses SOAP for communication

10. Henrik Bærbak Christensen
Micro Services
The next step? A successful step?
Henrik Bærbak Christensen

11. Henrik Bærbak Christensen
Overview
Henrik Bærbak Christensen

12. Henrik Bærbak Christensen
Key Properties
Henrik Bærbak Christensen

13. Henrik Bærbak Christensen
Component = Service
I.e. the unit of reuse is
“services” in [Lewis et al. 2014]
Out-of-process, communicate using RPC or web service
Henrik Bærbak Christensen

14. Organizational Principle
Classic versus DevOps
Products, not projects
Smart endpoints and dumb pipes
REST, not enterprise service bus
Decentralized governance
DevOps
Henrik Bærbak Christensen

15. Henrik Bærbak Christensen
Data Management
Is decentralized
Each service has its own storage
Henrik Bærbak Christensen

16. Infrastructure Automation
Docker is an excellent example
Infrastructure-as-code
Henrik Bærbak Christensen

17. … And Design for Failure!
Circuit Breakers
Timeouts
Bulkhead
Henrik Bærbak Christensen

18. Henrik Bærbak Christensen
Evolutionary Design
Build replacable and upgradeable units
MVP: Minimal Viable Prototype
Henrik Bærbak Christensen