Execution Environments for Distributed Computing

Distributed Systems

EEDC34330

Master in Computer Architecture, Networks and Systems - CANS

Homework number: 1Group number: EEDC-7

Group members:

Georgia Christodoulidou – geochris71@gmail.com

Ioanna Tsalouchidou – ioannatsalouchidou@gmail.com

Maria Stylianou – marsty5@gmail.com

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Contents

• Definitions• Need for DS• Characteristics• Trade-offs• Examples• Differentiation with parallel systems• Challenges

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What is a Distributed System (DS)?

• No single definition for distributed systems

• Two representative definitions:• “A system in which hardware and software components located

at network computers communicate and coordinate their actions only by message passing.” ~ Coulouris

• “A distributed system is a collection of independent components that appear to the users of the system as a single computer.” ~ Tanenbaum

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What is a Distributed System (DS)?

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Why do we need DS?

• Workload distribution among the nodes

Performance improved

• Information distribution and sharing

• Resource sharing

Reliability

Data Preservation &

Replication

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Characteristics of DS

• Concurrent execution• Message passing communication• Resource sharing• No global clock• Lack of knowledge of the global state of the DS by

any single process

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Trade-offs

• Communication via insecure network

• Topology is not stable => Latency increases

• Message loss

• Bandwidth is limited

• Multiple administrators => Difficult to manage the system

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Examples of DS

• World Wide Web - www• Distributed File Systems - DFS• Database Systems• Distributed Operating Systems

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Differentiation with Parallel Systems

• No need of shared memory Communication via message passing

• No need of homogeneity DS consists of different types of hardware and software.

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Challenges

• Heterogeneity• Distribution transparency• Fault tolerance• Scalability• Concurrency• Openness• Security

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Challenges - Heterogeneity

• Inter-operation of the heterogeneous components• Differences between components in

• Operating systems• Hardware and Communication architectures• Programming languages• Software

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Challenges - Distribution Transparency

• The perception of the system as a whole and not as a collection of independent components

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Challenges - Fault Tolerance, Scalability

Fault Tolerance• Multiple failures

• Hardware• Software• Network

• Maintain availability despite failures!

Scalability• The system should

remain effective, even with a significant increase • in the number or

resources• in the number of users

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Challenges - Concurrency, Openness

Concurrency• Manage concurrent

access to shared resources• Scheduling• Dependencies• Deadlocks

Openness• Possibility of new

resource-sharing services to be added

• Available to be used by users

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Challenges - Security

• Resources should be used the way they are supposed to

• Only authorized users should access the resources• Confidentiality• Integrity• Availability• Non-repudiation

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Thank you!

Questions?