Characterisation of Distributed Systems

Question 1

What is a distributed system?

Answer 1

A system where hardware/software components located at networked computers communicate and coordinate their actions only by passing messages.

Question 2

What are the characteristics of a Distributed System? (3)

Answer 2

Concurreny
No global clock
Independent Failures

Question 3

Why are distributed systems used? (3)

Answer 3

To share resouces
To have redundency
To parallelise computation

Question 4

How do distributed systems improve redundency?

Answer 4

Better fault tolerence

Question 5

What are the current trends of DS?

Answer 5

Cloud Computing
Big Data
Decentralised networks
IoT
Edge Computing
Fog Computing

Question 6

What is cloud computing?

Answer 6

Moving core services to remote servers.

Interact through web browser/application to store/retreive data and use services.

Question 7

What are the new requirements of DS for handling Big Data? (4)

Answer 7

Volume: Quantity of data
Variety: Diversity of types of data
Velocity: Speed data is generated and needs to be processed.
Veracity: Quality and value of data

Question 8

What are the issues with centralised networks?

Answer 8

Single point of failure
Censorship
Bottlenecks

Question 9

What are examples of decentralised networks? (2)

Answer 9

Peer to peer

Blockchain

Question 10

What is edge computing?

Answer 10

Placing more powerful devices at the edge of networks to carry out computation where the data is generated.

Question 11

What is fog computing?

Answer 11

Deploying more powerful resources between the edge and the cloud to carry out computation very close to where data is generated.

Question 12

What are the challenges of DS? (7)

Answer 12

Heterogeneity, Openness, Scalability, Transparency, Concurrency, Quality of Service, Failure Handling

Question 13

What are the heterogeneity challenges of DS?

Answer 13

Different implementations of data, software, networks can make communicating between them difficult unless standards have been agreed and adopted.
Internet protocols mask network heterogeneity.

Question 14

What are openness challenges of DS?

Answer 14

An open system can be extended and reimplemented in different ways.
Requires key interfaces to be publish (similar to standardisation, but less formal and faster.)

Question 15

What are the scalability challenges of DS?

Answer 15

Controlling the cost of physical resources.
Controlling the performance loss.
Preventing software resources running out.
Avoiding performance bottlenecks (centralisation)

Question 16

What are the failure handling challenges for DS?

Answer 16

Detecting failure (Async, sync)
Masking failure
Tolerating Failure
Recovering from failure

Question 17

What are the concurrency challenges of DS?

Answer 17

Allowing multiple clients to access the same resources at the same time in a safe way that doesn’t harm throughput too much.

Question 18

What are the transparency challenges of DS?

Answer 18

Hiding the separation of the system from the user and application programmer.
Should be percevied as one system not individual components.

Question 19

What are the transparency types in DS? (8)

Answer 19

Access, Location, Concurrency, Performance, Failure, Scaling, Mobility, Replication

Question 20

What are the quality of service challenges of DS?

Answer 20

Ability to meet deadlines
Requires guarentees of sufficient resources to complete tasks
Difficult when workload increases.

Question 21

How can QoS be achived in a DS?

Answer 21

Using a resource manage to ensure QoS requirements are met.