Physcial and Architectural Models

Question 1

What is the general approach to modelling DS?

Answer 1

Use models to represent DS to capture their relevant aspects.
Develop general solutions for classes of distributed systems.
Reuse solutions for new DS.

Question 2

What are the baseline physical models?

Answer 2

Components located at computers.
Computers interconnected by a network
Components communicate by passing messages over the network.

Question 3

What are the types of physical model for DS?

Answer 3

Early DS : Homogeneity, small scale
Internet-scale DS: Internet network, Heterogeneity, Global Scope
Comtempory DS: Supports mobile, ubiquitous, cloud computing.
Distributed System of Systems: Progressive integration of existing DS.

Question 4

What does an architectural model describe?

Answer 4

Types of components involved
Interrelationships of components
Interaction between components

Question 5

What is an architecture validated on?

Answer 5

Availability
Performance
Adaptability
Security

Question 6

What are the two main aspects of architecture?

Answer 6

Architectural elements: Components, communication, roles, deployment
Archtectural patterns: Common strategies to combine the building blocks

Question 7

What are the communicating entities of a DS?

Answer 7

Processes communicating via inter-process channels.

Threads

Question 8

What are the communication paradigms of DS?

Answer 8

Direct and Indirect Communication

Question 9

How do processes communicate in Direct Communication?

Answer 9

Message passing

Sockets

Question 10

What are the limitations of RI and Interprocess Communication

Answer 10

Space coupling: Senders need to know how to reach the receivers (endpoints)
Time Coupling: Sends and recevies need to be up and running at the same time.

Question 11

What does indirect communication achieve?

Answer 11

Time and space decoupling between senders and receviers.

Question 12

What are examples of indirect communication?

Answer 12

Group communication

Publish-subscribe systems (MQTT)

Question 13

What are the roles and responsibilities in a Client-Server system?

Answer 13

Clients send requests to servers and receive responses back.

Clients enabled to access shared resources that are managed by servers.

Question 14

What are the roles and responsibilities of P2P networks?

Answer 14

All involved play similar roles.

Clients can become part of the network and provide their resources to support the service.

Question 15

What do P2P networks enable?

Answer 15

Decentralisation
Better load balancing
Better scalability

Question 16

What does placement impact in DS?

Answer 16

Performance, Reliability, Security

Question 17

What aspects should be taken into account when designing placement of DS?

Answer 17

Communication patterns
Reliablilty of machines
Application workload
Quality of communication channels

Question 18

What are the pros and cons of partioning data over servers?

Answer 18

Pros: Fault tolerence, load balancing
Cons: Need to ensure consistency

Question 19

What are the pros and cons for data replication over servers?

Answer 19

Pros: No overhead for data consistency
Cons: no real fault tolerence

Question 20

Where are caches located?

Answer 20

Proxy servers

Question 21

Why are caches used?

Answer 21

To provide a closer store of data.

Question 22

What are the key architectural patterns?

Answer 22

Layering and Tiering

Question 23

What is layering?

Answer 23

Logical organistaion of services into service layers.

Application, Middleware, OS, Hardware

Question 24

What does the middleware in layering aim to do?

Answer 24

Mask heterogeneity

Provide suitable programming extraction (RMI, Group Communication)

Question 25

What is tiering?

Answer 25

Physical organisation of layers.

Functionalities are turned into servers.