Module 1 - Intro

Question 1

What is a distributed system?

Answer 1

A collection of autonomous computing elements what appear to its users as a single coherent system

Question 2

What is a middleware?

Answer 2

A layer of software that separates applications from the underlying platforms

Question 3

What are 5 goals of distributed systems?

Answer 3

• Support resource sharing
• Making distribution transparent
• being open
• being scalable
• being highly available

Question 4

What a does “distribution transparent” mean

Give an example

Answer 4

The system hides the fact that processes and resources are physically distributed

Examples:

• They hide where a resource is physically located
• They hide that the data is replicated
• They hide failures
• They hide that resources may be shared by several processes

Question 5

What does a “open distributed system” mean

Answer 5

A system that offers components that can be easily used or integrated into other systems

Properties of an open system:

• interoperability
• composability
• extensibility
• separation of policy and mechanism

Question 6

What does a “scalable distributed system” mean

Answer 6

Scalability is a system’s ability to expand along three axes:

1. Size (number of users & resources)
2. Geography
3. Administration (multiple independent admins)

Being able to add resources and improve the performance of the system

Question 7

What are 3 anti-patterns for scalable distributed systems?

Answer 7

• Centralized services (a single server for all users)
• Centralized data (a single DB for all data
• Centralized algorithms (it isn’t scalable for the algorithms to assume a global view of the network)

Question 8

What are primitive common rules to improve scalability in a distributed system?

Answer 8

Batch processing
Replication of microservices
Partitioning of requests
Load balancing

The idea is to avoid the anti-patterns

Question 9

What are the 8 fallacies (false beliefs) of distributed systems? (given the network)

As in, what are NOT features of a distributed system?

Answer 9

• The network is reliable
• The network is secure
• The network is homogeneous
• The topology does not change
• Latency is zero
• Bandwidth is infinite
• Transport cost is zero
• There is a single administrator

Question 10

What does it mean for a network in a distributed system to be homogeneous

Answer 10

For the connections between microservices to all be the same bandwidth and latency

Question 11

In high performance computing, there are multiprocessor systems and multicomputer systems. Describe the difference between a multiprocessor and a multicomputer system.

Answer 11

A multiprocessor shares memory across the computing units, whereas a multicomputer passes messages between computing units (each computing unit has its own memory block)

Multiprocessor Systems = parallel computing
Multicomputer Systems = distributed computing

Question 12

What are characteristics of a shared memory system? (a system in which computing units share memory)

Answer 12

• Threads communicate together by accessing shared variables
• Requires shared variable primitives
• Useful for CPU intensive programs
• Parallel computing

Question 13

What are characteristics of Message passing systems (a system in which each computing unit has its own memory block)

Answer 13

• Processes must communicate by sending and receiving messages over a network
• More scalable but system must support messages
• Distributed computing

Question 14

What are “cluster computing systems”?

Answer 14

Cluster computing frameworks distribute CPU or I/O-intensive
jobs across multiple servers

Just like Hadoop

Question 15

What are the 4 computing layers that a cloud system is divided into? (think SaaS, IaaS, PaaS, HaaS)

Answer 15

Application - Web services

Platform - Software framework, Databases

Infrastructure - VMs, Blob Storage

Hardware - CPU, Memory, Disk

Question 16

Example of PaaS (Platform as a service)

Answer 16

AWS, Azure, GCP, Digial Ocean

Question 17

Example of IaaS (Infrastructure as a service)

Answer 17

AWS S3, AWS EC2, etc

Question 18

Describe how middleware can be used as a communication facilitator between client applications and server applications

Answer 18

The middleware layer sits in between the clients and the servers, interfaces with the client applications, and the server-side apps