Distributed SystemsPrinciples and Paradigms

Reza RafehArak University

1 INTRODUCTION1.1 DEFINITION AND CHARACTERISTICS OF A DISTRIBUTED SYSTEM 1.2 TYPES OF DISTRIBUTED SYSTEMS  2 ARCHITECTURES 2.1 ARCHITECTURAL STYLES 2.2 SYSTEM ARCHITECTURES  3 PROCESSES , THREADS, MIGRATION

4 COMMUNICATION 4.1 FUNDAMENTALS 4.2 Types of Communication 4.2.1 REMOTE PROCEDURE CALL 4.2.2 MESSAGE-ORIENTED COMMUNICATION 4.2.3 STREAM-ORIENTED COMMUNICATION 4.2.4 MULTICAST COMMUNICATION

5 NAMING 5.1 NAMES, IDENTIFIERS, AND ADDRESSES5.2 Structured Naming5.3 Attribute-Based Naming

6 Synchronization 6.1 Clock Synchronization6.2 Logical Clocks6.3 Mutual Exclusion6.4 Global Positioning of Nodes6.5 Election Algorithms

7 Consistency and Replication 7.1 INTRODUCTION 7.2 DATA-CENTRIC CONSISTENCY MODELS 7.3 CLIENT-CENTRIC CONSISTENCY MODELS 7.4 REPLICA MANAGEMENT 7.5 CONSISTENCY PROTOCOLS

8 Fault Tolerance8.1 Introduction8.2 Process Resilience8.3 Reliable Client-Server Communication8.4 Reliable Group Communication8.5 Disturbed Commit8.6 Recovery

9 Security9.1 Introduction9.2 Secure Channels9.3 Access Control9.4 Security Management

10 Disturbed Object-Based Systems 10.1 Architecture10.2 Processes10.3 Communication10.4 Naming10.5 Synchronization10.6 Consistency and Replication10.7 Fault Tolerance 10.8 Security

11 Disturbed File Systems 11.1 Architecture11.2 Processes11.3 Communication11.4 Naming11.5 Synchronization11.6 Consistency and Replication11.7 Fault Tolerance 11.8 Security

12 Disturbed Web-Based Systems 12.1 Architecture12.2 Processes12.3 Communication12.4 Naming12.5 Synchronization12.6 Consistency and Replication12.7 Fault Tolerance 12.8 Security

13 Disturbed Coordination-Based Systems 13.1 Architecture13.2 Processes13.3 Communication13.4 Naming13.5 Synchronization13.6 Consistency and Replication13.7 Fault Tolerance 13.8 Security

Definition of a Distributed System (1)

A distributed system is:

A collection of independent computers that appears to its

users as a singlecoherent system.

Definition of a Distributed System (2)

A distributed system organized as middleware. The middleware layer extends over multiple

machines, and offers each application the same interface.

Motivation and Goals

• Making resources available– Systems should allow for efficient and controlled access to and sharing of distributed resources

• Hiding distribution– Systems should look as if only a single computer system is running

• Openness– Systems should offer services according to standard rules that describe the syntax and semantics of those Services

• Scalability– Systems should scale with respect to size, geography, and administrative boundaries

FeaturesTransparency

Degree of Transparency

• A trade-off between a high degree of transparency and the performance of a system

• Full distribution transparency is simply impossible

Openness

• A system • Offer services according to standard rules• Such rules are formalized in protocols

• Interoperability• Different manufacturers can co-exist and work

together • Portability

• System A can be executed, without modification, on a different distributed system B

Scalability:Size scalable: easily add more users & recourses to the system

Geographically scalable: users & resources may lie far apart

Administratively scalable: it can still be easy to manage even if it spans independent administrative organizations

Scalability

Scalability

Characteristics of decentralized algorithms:

• No machine has complete information about the system state.

• Machines make decisions based only on local information.

• Failure of one machine does not ruin the algorithm.

• There is no implicit assumption that a global clock exists.

Scaling Techniques

• Three techniques for scaling• Hiding communication latencies• Distribution • Replication

Scaling Techniques (1)

1.4

The difference between letting:

a) a server or

b) a client check forms as they are being filled

Scaling Techniques (2)

1.5

An example of dividing the DNS name space into zones.

Pitfalls when Developing Distributed Systems

• 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 one administrator

Types of Distributed Systems: 

1- Distributed Computing Systems : Focus on computation Cluster Computing Systems Grid Computing Systems

2- Distributed Information Systems:Focus on interoperability Transaction Processing Systems Enterprise Application Integration (Exchange info via RPC or RMI)

3- Distributed Pervasive Systems (usually small, battery-powered systems, Mobile & wireless): Focus on mobile, embedded, communicating Home Systems (e.g. Smart phones, PDAs) Electronic Health care systems (Heart monitors, BAN: Body Area Networks) Sensor Networks (distributed Databases connected wirelessly)

Cluster Computing Systems

- Hooking up a collection of simple computers via high-speed networks to build a supercomputing environment - Mostly homogenous - Example: server clusters at Banks

Grid Computing Systems

- have a high degree of heterogeneity-Users and recourses from different organizations are brought together to allow collaboration (i.e. a V.O. = Virtual Organization) - Members belonging to the same V.O. have access rights to a common set of recourses (e.g. Police, FBI, and some local agencies may form a computing grid)

Transaction Processing Systems (1)

BEGIN_TRANSACTIONsalary1 = doctor1.getSalary()doctor1.setSalary(salary1 + bonus)salary2 = doctor2.getSalary()doctor2.setSalary(salary2 - bonus)END_TRANSACTION

Transaction Processing Systems (2)

Characteristic:• Atomic: The transaction happens

indivisibly.

• Consistent: The transaction does not violate system invariants.

• Isolated: Concurrent transactions do not interfere with each other.

• Durable: Once a transaction commits, the changes are permanent.

Transaction Processing Systems (3)

Transaction Processing Systems (4)

Enterprise Application Integration

-RPC (Remote Procedure Call) -RMI (Remote Method Invocation)

Distributed Pervasive Systems

• Embrace contextual changes• (a phone now is a web access device. A

device must continuously be aware of the fact that its environment may change)

• Encourage ad hoc composition• (used differently by different users, e.g.

PDA)

• Recognize sharing as the default• (easily read, store, manage, and share info)

Electronic Health Care Systems (1)

• Where and how should monitored data be stored?

• How can we prevent loss of crucial data?

• What infrastructure is needed to generate and propagate alerts?

• How can physicians provide online feedback?

• How can extreme robustness of the monitoring system be realized?

• What are the security issues and how can the proper policies be enforced?

Electronic Health Care Systems (2)

Monitoring a person in a pervasive electronic health care system, using (a) a local hub or - (b) a continuous wireless connection.

Sensor Networks (1)• How do we (dynamically) set up

an efficient tree in a sensor network?

• How does aggregation of results take place? Can it be controlled?

• What happens when network links fail?

Sensor Networks (2)

Organizing a sensor network database, while storing and processing data (a) only at the operator’s site or …

Sensor Networks (3)

Organizing a sensor network database, while storing and processing data … or (b) only at the sensors.