Physical and Architectural Models (Revision)

Question 1

What is the Baseline Physical Model for Distributed Systems?

Answer 1

-Components located in computers.
-Communicate via interconnected network. (by passing messages).

Question 2

What are the entities communicating in an Architectural model of a DS?

Answer 2

-System-oriented Perspective (what is running?)
-Program-oriented Perspective (how can I abstract what is running?)

Question 3

How do these entities communicate?

Answer 3

-Inter-process communication: Message Passing via Sockets.
-Remote Invocation:
1. Request-reply protocols (send a request and receive a response).
2. RPC (Remote Procedure Call): Request the execution of a remote function and receive a response.
3. RMI (Remote Method Invocation): Object-oriented RPC.

Question 4

What are the limitations of inter-process communication and Remote invocation?

Answer 4

Time coupling and Space coupling.

Question 5

What roles and responsibilities do these entities have?

Answer 5

Client-Server:
1.The client makes a request and the server responds.
2. The clients have access to shared resources managed by servers.
3. Servers might be clients of other servers.
P2P:
1.All clients play similar roles => evenly distributed workload.
2. Same program, same interfaces running on different machines.
3. Can improve scalability as it enables decentralized approaches.

Question 6

What does the placement of elements in DS impact?

Answer 6

Performance, Security and Scalability.

Question 7

What are some aspects we need to consider when designing the DS?

Answer 7

-Communication channels.
-Reliability.
-Quality of communication channels.
-Application workload.

Question 8

What are two types of element placement in DS?

Answer 8

1. Mapping of services to multiple servers. Data objects can be partitioned or replicated. Replication guarantees fault tolerance but no data consistency the partition the opposite.
2. Caching.

Question 9

What is Layering and Tiering? (See activity)

Answer 9

Layering (logical organization): Vertical organization of services into service layers
Tiering (physical organization): Adjacent to Layering, organizes functionality of a specific layer and places this functionality into servers.