Tutorial 2

Question 1

Scalability can be measured along three different dimensions, name them.

Answer 1

1. Size scalability
2. Geographic scalability
3. Administrative scalability

Question 2

Goals of size scalability

Answer 2

It is possible to add users and ressources without noticeable performance loss

Question 3

Challenges of size scalability

Answer 3

There are bottlenecks limiting the use of centalized servers
1. Processing speed
-> limited by number / speed of CPUs
2. Storage capacity
Single server may not be able to store all data
3.I/O transfer rate

Question 4

Goal of geographic scalability

Answer 4

Even if users/resources are far appart, make communication delays hardly noticeable

Question 5

Challenges of geographic scalability

Answer 5

1. Synchronous communication leads to slow service performance
2. Wide-area network communication is unreliable and suffers bandwidth limitations
3. Wide-area systems are limited for multipoint communication

Question 6

Goal of administrative scalability

Answer 6

System stays manageable even if there are many independent organizations involved

Question 7

Challenges of administrative scalability

Answer 7

1. Missing trust between different organizations (especially in different countries)
2. Conflicting policies regarding payment and management
3. Security issues

Question 8

Techniques to solve scalability problems in distrbuted systems

Answer 8

1. Improving capacities of servers and network (inc. memory and upgrade CPU’s)
2. Hide communication latencies
3. Partitioning and distribution
4. Replication

Question 9

Name 4 architectural styles for distributed systems

Answer 9

1. Layered
2. Object based and service oriented
3. Resource based
4. Publish - subscribe

Question 10

Why are there different architectural styles for distributed systems?

Answer 10

Not every architecture suitable for every use case

Question 11

Briefly explain Layered Architecture

Answer 11

1. High abstraction
2. Components are assigned different function layers with clear data flow Not easy to deploy!
3. Coupled and monolithic implementations

Question 12

Briefly explain Object- or service based architecture

Answer 12

1. Easier to integrate services from different administrative organizations
2. However, connecting components of service is challenging

Question 13

Briefly explain Resouce based architecture

Answer 13

1. System as a huge collection of resources managed by components
2. Use generic operations (simplicity) .RESTful architectures
3. Prone to errors during runtime
4. Complicate communication schemes

Question 14

Briefly explain publish-subsribe architecture

Answer 14

Strong decoupling of processes, but event-composition is not a trivial task