Tutorial 1

Question 1

What is a Distributed System ?

Answer 1

Is a collection of autonomous computing elements that appears to its users as a single coherent system

Question 2

What does a collection of autonomous computing elements mean?

Answer 2

1. Different types of nodes ( computing elements) i.e hardware devices or software process
2. Act independently but try to achieve a common goal.

Question 3

What do we understand with ‘System appears to users as a single system’ ?

Answer 3

1. System behaves according to the expectations
2. Collection of nodes operates the same independent of location, time, and type of interaction.
3. Hide internal organization
4. Hide different computing elements

Question 4

Explain the concept of transparency in distributed systems

Answer 4

A transparent system appears to its users as a single computer, hides the distribution of processes and resources

Question 5

Some types of transparency

Answer 5

1. Location
2. Access
3. Migration
4. Relocation
5. Replication
6. Concurrency
7. Failure

Question 6

Why is implementing the highest degree of transparency not always a good idea?

Answer 6

1. Might cause an unaccepted loss of performance
2. Context/Location is sometimes required
3. Legal reasons such as privacy

Question 6

High transparency might cause an unaccepted loss of performance. Explain

Answer 6

1. Transmission is limited by processing capacities and delays in intermediate switches
2. Ensuring consistency between replicas needs seconds to be complete, which can’t be hidden from clients
3. Masking transient server failure through repeatedly attempting to contact the server can slow down the whole system

Question 7

Give examples on how forcing transparency can impact the performance of a distributed system.

Answer 7

1. Location transparency: Storing data in servers that could be geographically distant
2. Replication transparency: Consistency between data copies requires continuous propagation of changes

Question 8

What mechanisms are needed for hiding the occurrence and recovery from failures
in a distributed system and what are the challenges?

Answer 8

1.Replication of resources provides high availability
2.Mechanisms of access and relocation transparency
Challenges :
1. There are high economical and performance costs for replication
2. Find adequate backup strategies
3. Mechanisms for detecting failures

Question 9

Describe openess briefly

Answer 9

Components from different sources integrated into a single system

1. Owned components used by other systems
2. Use components from other systems

Question 10

What are the main goals of openness and how could they be achieved?

Answer 10

1. Interoperability: Cooperation with other open systems
2. Portability: Allow applications to be easily ported between different implementations of the system but with the same interfaces
3. Extensibility: Allow easy configuration, integration, and replacement of components

Question 11

How can the goals of openess be achieved?

Answer 11

1. Complete and neutral inferfaces
   2.Seperating policy from mechanism
   Tutorial 1. Page 9

Question 12

“Middleware is the same to a distributed system as what an operating system is to a computer”. Explain this sentence.

Answer 12

Middleware and OS as resource managers
OS:
1.Manage hard- and software
2.Resource scheduling
3.Control interaction among processes/ threads/ computations
Middleware:
1.Enables interoperability between components with different OS ,different locations,etc.
2.Control interaction between components through coordination,naming,communication(e.g.
prevent concurrent computations from interfering)