Distributed Systems
Principles and Paradigms
Reza Rafeh
Arak University
1 INTRODUCTION
1.1 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 ADDRESSES
5.2 Structured Naming
5.3 Attribute-Based Naming
6 Synchronization
6.1 Clock Synchronization
6.2 Logical Clocks
6.3 Mutual Exclusion
6.4 Global Positioning of Nodes
6.5 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 Tolerance
8.1 Introduction
8.2 Process Resilience
8.3 Reliable Client-Server Communication
8.4 Reliable Group Communication
8.5 Disturbed Commit
8.6 Recovery
9 Security
9.1 Introduction
9.2 Secure Channels
9.3 Access Control
9.4 Security Management
10 Disturbed Object-Based Systems
10.1 Architecture
10.2 Processes
10.3 Communication
10.4 Naming
10.5 Synchronization
10.6 Consistency and Replication
10.7 Fault Tolerance
10.8 Security
11 Disturbed File Systems
11.1 Architecture
11.2 Processes
11.3 Communication
11.4 Naming
11.5 Synchronization
11.6 Consistency and Replication
11.7 Fault Tolerance
11.8 Security
12 Disturbed Web-Based Systems
12.1 Architecture
12.2 Processes
12.3 Communication
12.4 Naming
12.5 Synchronization
12.6 Consistency and Replication
12.7 Fault Tolerance
12.8 Security
13 Disturbed Coordination-Based Systems
13.1 Architecture
13.2 Processes
13.3 Communication
13.4 Naming
13.5 Synchronization
13.6 Consistency and Replication
13.7 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 single coherent 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
Features
Transparency
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, batterypowered 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_TRANSACTION
salary1 = 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.