Lesson 1: Introduction

Question 1

Give an informal definition of a distributed system

Answer 1

A distributed system is a collection of independent computers that appears to its user as a single coherent system.
-> build a powerful system out of many simpler systems

Question 2

What is a remote invocation?

Answer 2

A remote invocation is the complete interaction between client and server to process a single request

Question 3

What is a server?

Answer 3

It is a running process on a networked computer.
It accepts requests to perform a service and will respond appropriately.

Question 4

What is a service?

Answer 4

= part of a computer system managing a collection of related resources, presenting their functionality to users and applications.

Question 5

Define a “client”

Answer 5

It is a running process on a networked computer sending service requests to servers.

Question 6

Give 6 reasons to choose for distributed systems (keywords)

Answer 6

• Cost
• Capability
• Concurrency
• Reliability
• Integration
• Distribution

Question 7

Explain why “cost” is a reason to choose for distributed systems

Answer 7

Networked commodity systems can render the best performance/$

Question 8

Explain why “capability” is a reason to choose for distributed systems

Answer 8

Many computational problems are too large for any single system because of memory, data storage and computational requirements

Question 9

Explain why “concurrency” is a reason to choose for distributed systems

Answer 9

Many ‘large’ problems have inherent options for parallelism

Question 10

Explain why “reliability” is a reason to choose for distributed systems

Answer 10

Distributing redundant components minimizes the probability faults impact the user.

Question 11

Explain why “integration” is a reason to choose for distributed systems

Answer 11

• For organizations to interact, their systems need to interact
• Highly specialized infrastructures need to be integrated and shared

Question 12

Explain why “distribution” is a reason to choose for distributed systems

Answer 12

e-mail, WWW,… are inherently distributed as users are geographically spread

Question 13

What are todays problems and challenges with distributed systems?

Answer 13

1) No limit on spatial extent, difficult to manage
2) No global time notion
3) Almost always concurrent execution
4) (partial) failures likely to happen

Question 14

What are the the two main differences between coupled and de-coupled architectures?

Answer 14

In coupled architectures components are tightly linked with each other and removing/adding a component is non-trivial.

In de-coupled architectures components are loosely linked with each other and removing/adding a component is easier and can happen frequently

Question 15

Give the two coupled architectures seen in class.

Answer 15

We have seen the layered and object-based architecture.

Question 16

What is the layered architecture?

Answer 16

It is a coupled architecture.
-> layer only interacts with neighbor

Question 17

Give the ups and downs of the layered architecture.

Answer 17

+ reduced number of interfaces, dependencies
+ easy replacement of a layer

[-] possible duplication of functionality

Question 18

What is the object-based architecture?

Answer 18

It is a coupled architecture.
Interacting objects, no predefined interaction patterns

Question 19

Give the ups and downs of the object-based architecture.

Answer 19

+ highly flexible
- complex to manage and maintain

Question 20

What is the event-based architecture?

Answer 20

It is a decoupled architecture.
“publish-subscribe” style
Often used to integrate legacy systems

Question 21

Give the ups and downs of the event-based architecture

Answer 21

+ loosely coupling of components

Question 22

What is the data-centric architecture?

Answer 22

It is a de-coupled architecture. The only interaction is through a shared database

Question 23

Give the ups and down of a data-centric architecture.

Answer 23

+ loosely coupling of components
- possibly slow (central bottleneck, locking,…)

Question 24

What are peer-to-peer architectures?

Answer 24

Architectures to deliver a service that is fully decentralized and self-organizing.
Processes (nodes) are organized in an overlay network (virtual network)

Question 25

Give 6 characteristics of the peer-to-peer architecture

Answer 25

• Each node fulfills both a client and a server role
• Nodes and data item keys are assigned Globally Unique Identifiers
• Nodes have no or limited direct knowledge on other nodes
• Application-level message routing
• Nodes are volatile
• Structured or unstructured

Question 26

what is the service interface?

Answer 26

The service interface restricts access to the underlying resources of the service through a well-defined set of operations.