Lecture 1-introduction to distributed computing.pptx

Distributed and
Cloud Computing
DR. ABDULRAHMAN ALSABRI
ALSABRI374@GMAIL.COM

Computing Systems
Types of Computing Systems:
Centralized Systems
Decentralized Systems
Distributed Systems
 Distributed Computing :
A field of computer science /engineering that
studies distributed systems.

Centralized,
Decentralized and
Distributed Systems

Centralized Systems
Centralized systems are systems that use
client/server architecture where one or more
client nodes are directly connected to a
central server where client sends a request
to the server and receives the response.
 Components of Centralized System –
1. Node (Computer, Mobile, etc.).
2. Server.
3. Communication link (Cables, Wi-Fi, etc.).

Characteristics of Centralized System
 Presence of a global clock:
As the entire system consists of a central node(a server/ a master) and
many client nodes(a computer/ a slave), all client nodes sync up with the
global clock(the clock of the central node).
 One single central unit:
 One single central unit which serves/coordinates all the other nodes in
the system.
 Dependent failure of components:
Central node failure causes entire system to fail. This makes sense because
when the server is down, no other entity is there to send/receive
response/requests

Advantages of Centralized
System
 Easy to physically secure. It is easy to secure and service the server and
client nodes by virtue of their location
 Smooth and elegant personal experience – A client has a dedicated system
which he uses(for example, a personal computer) and the company has a
similar system which can be modified to suit custom needs
 Dedicated resources (memory, CPU cores, etc)
More cost efficient for small systems upto a certain limit – As the central
systems take less funds to set up, they have an edge when small systems
have to be built
Quick updates are possible – Only one machine to update.
 Easy detachment of a node from the system. Just remove the connection
of the client node from the server and voila! Node detached.

Disadvantages of Centralized
System
Highly dependent on the network connectivity – System can fail if the
nodes lose connectivity as there is only one central node.
No graceful degradation of system – abrupt failure of the entire
system
Less possibility of data backup. If the server node fails and there is no
backup, you lose the data straight away
Difficult server maintenance – There is only one server node and due
to availability reasons, it is inefficient and unprofessional to take the
server down for maintenance. So, updates have to be done on-the-
fly(hot updates) which is difficult and the system could break.

Applications of Centralized System
 Application development : Very easy to setup a
central server and send client requests.
 Data analysis – Easy to do data analysis when all
the data is in one place and available for analysis
 Personal computing

Use Cases
 Centralized databases – all the data in one server
for use.
 Single player games like Need For Speed, GTA
Vice City – entire game in one system(commonly, a
Personal Computer)
 Application development by deploying test
servers leading to easy debugging, easy
deployment, easy simulation
 Personal Computers

Decentralized Systems
 Is an interconnected information
system in which no single entity is the
sole authority.
Every node makes its own decision. The
final behavior of the system is the
aggregate of the decisions of the
individual nodes.
Components of Centralized System:
1. Nodes (Computer, Mobile, etc.).
2. Servers
3. Communication link (Cables, Wi-Fi,
etc.).

Ingredients of a Distributed System
Middleware
Network OS
Component-1 Component-n
…
Host-1
Hardware
Middleware
Network OS
…
Host-3
Hardware
Middleware
Network OS
…
Host-n
Hardware
Middleware
Network OS
…
Host-2
Hardware
Network

Characteristics of Decentralized System
Lack of a global clock: Every node is independent of each
other and hence, have different clocks that they run and
follow.
Multiple central units (Computers/Nodes/Servers): More
than one central unit which can listen for connections from
other nodes
Dependent failure of components: one central node failure
causes a part of system to fail; not the whole system

Architecture of Decentralized System
Peer-to-peer architecture :
 all nodes are peers of each other. No one node has supremacy over
other nodes
 Master-slave architecture :
 One node can become a master by voting and help in coordinating
of a part of the system but this does not mean the node has
supremacy over the other node which it is coordinating

Advantages of Decentralized System
 Minimal problem of performance bottlenecks occurring :
The entire load gets balanced on all the nodes; leading to
minimal to no bottleneck situations.
 High availability: Some nodes(computers, mobiles,
servers) are always available/online for work, leading to
high availability.
 More autonomy and control over resources : As each
node controls its own behavior, it has better autonomy
leading to more control over resources

Disadvantages of Decentralized System
 Difficult to achieve global big tasks : No chain of
command to command others to perform certain tasks
Difficult to know which node failed : Each node must be
pinged for availability checking and partitioning of work has
to be done to actually find out which node failed by
checking the expected output with what the node
generated
 Difficult to know which node responded : When a
request is served by a decentralized system, the request is
actually served by one of the nodes in the system but it is
actually difficult to find out which node indeed served the
request.

Applications of Decentralized System
 Private networks : peer nodes joined with each other
to make a private network.
Cryptocurrency: (Blockchain ) Nodes joined to
become a part of a system in which digital currency is
exchanged without any trace and location of who sent
what to whom.
Decentralized databases : Entire database split in parts
and distributed to different nodes for storage and use.

DISTRIBUTED SYSTEMS
A distributed system is a
collection of autonomous hosts
that are connected through a
computer network each host
executes components and
coordinated via middleware.
Components of Distributed System –
1. Node (Computer, Mobile, etc.)
2. Communication link (Cables, Wi-Fi, etc.)

Characteristics of Distributed System
Concurrency of components: Nodes apply consensus
protocols to agree on same
values/transactions/commands/logs.
A global clock is not required : All nodes maintain their
own clock.
Independent failure of components: In a distributed
system, nodes fail independently without having a significant
effect on the entire system.

Architecture of Distributed System
peer-to-peer : all nodes are peer of each other
and work towards a common goal
client-server : some nodes are become server
nodes for the role of coordinator, arbiter, etc.
n-tier architecture : different parts of an
application are distributed in different nodes of the
systems and these nodes work together to function
as an application for the user/client

Advantages of Distributed System
Economics:-
◦ Computers harnessed together give a better price/performance ratio
than mainframes.
Speed:-
◦ A distributed system may have more total computing power than a
mainframe.
Reliability:-
◦ If one machine crashes, the system as a whole can still survive if you
have multiple server machines and multiple storage devices
(redundancy).
Extensibility and Incremental Growth:-
◦ Possible to gradually scale up (in terms of processing power and
functionality) by adding more sources (both hardware and software).
This can be done without disruption to the rest of the system.

Disadvantages of Distributed System
Complexity :-
◦ Lack of experience in designing, and implementing a distributed
system. E.g. which platform (hardware and OS) to use, which
language to use etc.
Network problem:-
◦ If the network underlying a distributed system saturates or goes
down, then the distributed system will be effectively disabled thus
negating most of the advantages of the distributed system.
Security:-
◦ Security is a major hazard since easy access to data means easy
access to secret data as well.

Applications of Distributed System
 Cluster computing – a technique in which many
computers are coupled together to work so that they
achieve global goals. The computer cluster acts as if they
were a single computer
Grid computing – All the resources are pooled together for
sharing in this kind of computing turning the systems into a
powerful supercomputer; essentially.

Issues and Challenges
 Heterogeneity of components :-
◦ variety or differences that apply to computer hardware, network, OS,
programming language and implementations by different developers.
 Openness:-
◦ System can be extended and re-implemented in various ways.
Transparency:-
◦ make certain aspects of distribution are invisible to the application
programmer ; focus on design of their particular application.
◦ They not concern the locations and details of how it operate, either
replicated or migrated.

Issues and Challenges cont…
Security:-
◦ Security for information resources in distributed system have 3 components :
a. Confidentiality : protection against disclosure to unauthorized individuals.
b. Integrity : protection against alteration/corruption
c. Availability : protection against interference with the means to access the
resources.
Concurrency :-
◦ Where applications/services process concurrency, it will effect a
conflict in operations with one another and produce
inconsistence results.
◦ Each resource must be designed to be safe in a concurrent
environment.

Distributed Systems Architecture
Client-server
3-tier architecture
Peer-to-peer

Client/Server Architecture
Client/server architecture is a
computing model in which the server
hosts, delivers and manages most of the
resources and services to be consumed
by the client.
Components
Server
 Hosts Services
Client
 Request Service
Communication
Media for message exchange

Peer-to-Peer Architecture (P2P Architecture)
Peer-to-peer architecture (P2P
architecture) is a commonly used
computer networking architecture in
which each workstation, or node,
has the same capabilities and
responsibilities.

3-Tier Client Server System
 A three-tier architecture is a client-server architecture in
which the functional process logic, data access, computer
data storage and user interface are developed and
maintained as independent modules on separate platforms.

3-Tier Client Server System
Presentation Tier- The presentation tier is the
front end layer in the 3-tier system and consists of
the user interface.
Application Tier- The application tier contains the
functional business logic .
Data Tier- The data tier comprises of the
database/data storage system and data access
layer.

21-Oct-22 COMP28112 LECTURE 3 32
Client-Server vs P2P
Client-Server
◦ Widely Used
◦ Functional Specialisation
◦ Asymmetrical
◦ Tends to be centralised
◦ Tends to scale poorly
P2P
◦ Symmetrical, computers have same
“rights”
◦ Truly Distributed
◦ Share / exploit resources with a
large number of participants
◦ Resource discovery is a challenge

Distributed Computing Systems
Clusters
Grids
Clouds

Cluster Computing
A collection of similar processors (PCs, workstations)
running the same operating system, connected by a high-
speed LAN.
Each node set to perform the same task, controlled and
scheduled by software.
Parallel computing capabilities using inexpensive PC
hardware
High degree of distribution transparency (single system
image)(SSI)
Processes can migrate between nodes dynamically and
preemptively

Components of Cluster
CPU CPU CPU
…
High Speed Local Network
Cluster Middle ware
Cluster
…
 Nodes(master+computing)
 Network
 OS
 Cluster middleware:
Middleware such as MPI
which permits compute
clustering programs to be
portable to a wide variety
of clusters

Grid Computing Systems
Similar to clusters but processors are more loosely coupled, tend to be
heterogeneous, and are not all in a central location.
Highly heterogeneous with respect to hardware, software, networks,
security policies, etc.
A collaboration of users who pool resources (servers, storage, databases,
clusters,..) and share them
Can handle workloads similar to those on supercomputers, but grid
computers connect over a network (Internet?) and supercomputers’ CPUs
connect to a high-speed internal bus/network.
Each user should have a single login account to access all resources.
Resources may be owned by diverse organizations.
.

Architecture for Grid Systems
Fabric layer: interfaces to local resources at
a specific site
Connectivity layer: protocols to support
usage of multiple resources for a single
application; e.g., access a remote resource
or transfer data between resources; and
protocols to provide security
Resource layer manages a single resource,
using functions supplied by the connectivity
layer
Collective layer: resource discovery,
allocation, scheduling, etc.
Applications: use the grid resources
The collective, connectivity and resource
layers together form the middleware layer
for a grid
. A layered architecture for grid
computing systems

Cloud computing
Is the delivery of computing services—servers, storage,
databases, networking, software, analytics and more—over
the Internet
Is the delivery of on-demand computing services -- from
applications to storage and processing power -- typically over the
internet and on a pay-as-you-go basis.
is an information technology (IT) paradigm that enables
ubiquitous access to shared pools of virtualized and
configurable system resources and higher-level services that can
be rapidly provisioned with minimal management effort, often
over the Internet.

Lecture 1-introduction to distributed computing.pptx

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Lecture 1-introduction to distributed computing.pptx