This document discusses different types of distributed system architectures. It covers layered architectures where components are organized in layers and requests flow from top to bottom. Object-based architectures connect components through remote procedure calls. Data-centered architectures involve all components communicating through a shared data repository. Event-based architectures use publish-subscribe systems where components communicate through event propagation. The document also describes centralized client-server architectures and decentralized peer-to-peer architectures. Client-server involves clients requesting from servers, while peer-to-peer has no central control and nodes can act as clients or servers.

1. Chapter 2(A) – Distributed System
Architectures

2. • The content of this chapter is structured as follows:
 Software architectural
 Layered architectures
 Object-based architectures
 Data-centered architectures
 Event-based architectures
 System architectures
 Client-server architecture
 Peer-to-peer (P2P) architecture
Introduction
20.11.2022 2

3. 2.1. Why we need Architectures
 For hardware and software arrangement
 This arrangement is generally known as a topology
 The ways on how to view the organization of software
components and how they should interact
 Distributed system architectures are bundled up with components and
connectors.
– Component: A modular unit with well-defined interfaces; replaceable;
reusable
– Connector: A communication link between modules
• e.g., facilities for RPC, message/file passing, or streaming data
20.11.2022 3

4. 2.2. Architectural Styles
 There are various architectural styles
A) Layered architectures
B) Object-based architectures
C) Data-centered architectures
E) Event-based architectures
20.11.2022 4

5. 2.2. Architectural Styles
A) Layered architectures:
 Components are organized in a layered fashion where a
 The layers on the bottom provide a service to the layers on the top.
• Which means request flows from top to bottom,
• The response is sent from bottom to top.
 A well known example for this is the OSI model that
incorporates a layered architecture
the layered architectural style
20.11.2022 5

6. 2.2. Architectural Styles……
A) Layered architectures…..
20.11.2022 6

7. B) Object-based architectures:
 Each object corresponds to a component and
 The components are connected through a remote procedure
call mechanism (client-server paradigm)
 No specific architecture like layers
 No sequential step like layers
the object-based architectural style
2.2. Architectural Styles……
20.11.2022 7

8. 2.2. Architectural Styles……
B) Object-based architectures……
 Communication between object happen as method
invocations.
These are generally called Remote Procedure Calls
(RPC).
 Some popular examples are
 Java RMI,
 Web Services and
 REST API Calls.
 This has the following properties.
 This architecture style is less structured.
 Component object
 Connector RPC or RMI
20.11.2022 8

9. 2.2. Architectural Styles……
C) Data-centered architectures
 All components communicate through a common repository;
e.g., a shared distributed file system
 It contains all the required data in one place
 It follows publish/subscribe type of communication.
 Distributed file systems, and
 Web based data services
20.11.2022 9

10. 2.2. Architectural Styles……
D ) Event-based architectures:
 Components communicate through the propagation of
events.
 It uses Publish/subscribe systems
 How It works?
 Step-1: An event is generated.
 Step-2: It will be sent to the bus system.
 Step-3: With this, everyone else will be notified telling
that such an event has occurred.
 So, if anyone is interested, that node can pull the
event from the bus and use it.
 Sometimes these events could be data, or event
URLs to resources.
20.11.2022 10

11. 2.2. Architectural Styles……
D ) Event-based architectures…..
 Easy to add, remove and modify components in the
system. S
 Some examples are, publisher - subscriber system, and
Enterprise Services Bus (ESB).
the event-based architectural style
20.11.2022 11

12. 2.2 System Architectures
Two major system-level architectures:
A. Centralized Architectures
e.g., client-server architectures
B. Decentralized Architectures
e.g., p2p
. .
20.11.2022 12

13. 20.11.2022 13
2.2 System Architectures
A) Centralized Architecture: e.g., Client-server architecture
 It consists of a client and a server.
 The client can then request from the server, and the server
will respond accordingly.

14. More on Client-server architecture
general interaction between a client and a server
20.11.2022 14
 Client-server architecture has been subjected to many database-
based applications.
 Client-server applications usually have three different layers
 The user-interface level: implemented by clients and contains all that
is required by a client; usually through GUIs, but not necessarily
 The processing level: contains the applications
 The data level: contains the programs that maintain the actual data

15. • e.g., the general organization of an Internet search engine into three
different layers
 There is a question in Client-Server Architectures
 Questions: how to physically distribute a client-server application
across several machines
 Solution: Multi-tiered Architectures, e.g., Two-tiered architecture

16. Multi-tiered Architectures
(a) put only terminal-dependent part of the user interface on the client machine and let
the applications remotely control the presentation
(b) put the entire user-interface software on the client side
(c) move part of the application to the client, e.g. checking correctness in filling forms
(d) and (e) are for powerful client machines (more popular)
20.11.2022 16
Two-tiered architecture: alternative client-server organizations

17. Multi-tiered Architectures
 an example is the organization of Web sites
20.11.2022 17
three-tiered architecture: an example of a server acting as a client

18. More on Client-server architecture…..
• Advantages:
– Easier to Build and Maintain
– Better Security
– Stable
• Disadvantages:
– Single point of failure
– Less scalable
20.11.2022 18

19. 2.2 System Architectures…..
B) Decentralized Architectures: e.g., Peer-to-peer (P2P) architecture
– P2P is a good example for decentralized
architectures
 Removes distinction between a client and a server
 Works on the concept of no central control in a distributed system
 A node can either act as a client or server at any given time once it
joins the network.
 A node that requests something is called a client
 A node that provides response is called a server
20.11.2022 19

20. Decentralized Architectures….
 Two major decentralized forms of architectures
 Vertical distribution:
 Place logically different components on different
machines
 Horizontal distribution:
 Physically split up the client or the server into logically
equivalent parts
 an example is a peer-to-peer system where processes are
equal and hence each process acts as a client and a
server at the same time
 read about the different approaches of peer-to-peer
architecture - pages 44 - 51 and about Architectures versus
Middleware - pages 54 - 66
20.11.2022 20

21.  another example is the horizontal distribution of a Web
service
20.11.2022 21

22. 2.3 Client-Server Vs. Peer-to-Peer Architectures
20.11.2022 22

23. The end
20.11.2022 23