DISTRIBUTED SYSTEMS. Second Edition. Andrew S. Tanenbaum Maarten Van Steen. Vrije Universiteit Amsterdam, 7'he Netherlands PEARSON.

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1 DISTRIBUTED SYSTEMS 121r itac itple TAYAdiets Second Edition Andrew S. Tanenbaum Maarten Van Steen Vrije Universiteit Amsterdam, 7'he Netherlands PEARSON Prentice Hall Upper Saddle River, NJ 07458

2 CONTENTS PREFACE xvii 1 INTRODUCTION DEFINITION OF A DISTRIBUTED SYSTEM GOALS Making Resources Accessible Distribution Transparency Openness Scalability Pitfalls TYPES OF DISTRIBUTED SYSTEMS Distributed Computing Systems Distributed Information Systems Distributed Pervasive Systems SUMMARY 30 2 ARCHITECTURES ARCHITECTURAL STYLES SYSTEM ARCHITECTURES Centralized Architectures Decentralized Architectures Hybrid Architectures ARCHITECTURES VERSUS MIDDLEWARE Interceptors General Approaches to Adaptive Software Discussion 58 vii

3 viii CONTENTS 2.4 SELF-MANAGEMENT IN DISTRIBUTED SYSTEMS The Feedback Control Model Example: Systems Monitoring with Astrolabe Example: Differentiating Replication Strategies in Globule Example: Automatic Component Repair Management in Jade SUMMARY 66 3 PROCESSES THREADS Introduction to Threads Threads in Distributed Systems VIRTUALIZATION The Role of Virtualization in Distributed Systems Architectures of Virtual Machines CLIENTS Networked User Interfaces Client-Side Software for Distribution Transparency SERVERS General Design Issues Server Clusters Managing Server Clusters CODE MIGRATION Approaches to Code Migration Migration and Local Resources Migration in Heterogeneous Systems SUMMARY COMMUNICATION FUNDAMENTALS Layered Protocols Types of Communication REMOTE PROCEDURE CALL Basic RPC Operation Parameter Passing 130

4 CONTENTS ix Asynchronous RPC Example: DCE RPC MESSAGE-ORIENTED COMMUNICATION Message-Oriented Transient Communication Message-Oriented Persistent Communication Example: IBM's WebSphere Message-Queuing System STREAM-ORIENTED COMMUNICATION Support for Continuous Media Streams and Quality of Service Stream Synchronization MULTICAST COMMUNICATION Application-Level Multicasting Gossip-Based Data Dissemination SUMMARY NAMING NAMES, IDENTIFIERS, AND ADDRESSES FLAT NAMING Simple Solutions Home-Based Approaches Distributed Hash Tables Hierarchical Approaches STRUCTURED NAMING Name Spaces Name Resolution The Implementation of a Name Space Example: The Domain Name System ATTRIBUTE-BASED NAMING Directory Services Hierarchical Implementations: LDAP Decentralized Implementations SUMMARY

5 x CONTENTS 6 SYNCHRONIZATION CLOCK SYNCHRONIZATION Physical Clocks Global Positioning System Clock Synchronization Algorithms LOGICAL CLOCKS Lamport's Logical Clocks Vector Clocks MUTUAL EXCLUSION Overview A Centralized Algorithm A Decentralized Algorithm A Distributed Algorithm A Token Ring Algorithm A Comparison of the Four Algorithms GLOBAL POSITIONING OF NODES ELECTION ALGORITHMS Traditional Election Algorithms Elections in Wireless Environments Elections in Large-Scale Systems SUMMARY CONSISTENCY AND REPLICATION INTRODUCTION Reasons for Replication Replication as Scaling Technique DATA-CENTRIC CONSISTENCY MODELS Continuous Consistency Consistent Ordering of Operations CLIENT-CENTRIC CONSISTENCY MODELS Eventual Consistency Monotonic Reads Monotonic Writes Read Your Writes Writes Follow Reads 295

6 CONTENTS xi 7.4 REPLICA MANAGEMENT Replica-Server Placement Content Replication and Placement Content Distribution CONSISTENCY PROTOCOLS Continuous Consistency Primary-Based Protocols Replicated-Write Protocols Cache-Coherence Protocols Implementing Client-Centric Consistency SUMMARY FAULT TOLERANCE INTRODUCTION TO FAULT TOLERANCE Basic Concepts Failure Models Failure Masking by Redundancy PROCESS RESILIENCE Design Issues Failure Masking and Replication Agreement in Faulty Systems Failure Detection RELIABLE CLIENT-SERVER COMMUNICATION Point-to-Point Communication RPC Semantics in the Presence of Failures RELIABLE GROUP COMMUNICATION Basic Reliable-Multicasting Schemes Scalability in Reliable Multicasting Atomic Multicast DISTRIBUTED COMMIT Two-Phase Commit Three-Phase Commit RECOVERY Introduction Checkpointing 366

7 xii CONTENTS Message Logging Recovery-Oriented Computing SUMMARY SECURITY INTRODUCTION TO SECURITY Security Threats, Policies, and Mechanisms Design Issues Cryptography SECURE CHANNELS Authentication Message Integrity and Confidentiality Secure Group Communication Example: Kerberos ACCESS CONTROL General Issues in Access Control Firewalls Secure Mobile Code Denial of Service SECURITY MANAGEMENT Key Management Secure Group Management Authorization Management SUMMARY DISTRIBUTED OBJECT-BASED SYSTEMS ARCHITECTURE Distributed Objects Example: Enterprise Java Beans Example: Globe Distributed Shared Objects PROCESSES Object Servers Example: The Ice Runtime System 454

8 CONTENTS xiii 10.3 COMMUNICATION Binding a Client to an Object Static versus Dynamic Remote Method Invocations Parameter Passing Example: Java RMI Object-Based Messaging NAMING CORBA Object References Globe Object References SYNCHRONIZATION CONSISTENCY AND REPLICATION Entry Consistency Replicated Invocations FAULT TOLERANCE Example: Fault-Tolerant CORBA Example: Fault-Tolerant Java SECURITY Example: Globe Security for Remote Objects SUMMARY DISTRIBUTED FILE SYSTEMS ARCHITECTURE Client-Server Architectures Cluster-Based Distributed File Systems Symmetric Architectures PROCESSES COMMUNICATION RPCs in NFS The RPC2 Subsystem File-Oriented Communication in Plan NAMING Naming in NFS Constructing a Global Name Space 512

9 xiv CONTENTS 11.5 SYNCHRONIZATION Semantics of File Sharing File Locking Sharing Files in Coda CONSISTENCY AND REPLICATION Client-Side Caching Server-Side Replication Replication in Peer-to-Peer File Systems File Replication in Grid Systems FAULT TOLERANCE Handling Byzantine Failures High Availability in Peer-to-Peer Systems SECURITY Security in NFS Decentralized Authentication Secure Peer-to-Peer File-Sharing Systems SUMMARY DISTRIBUTED WEB-BASED SYSTEMS ARCHITECTURE Traditional Web-Based Systems Web Services PROCESSES Clients The Apache Web Server Web Server Clusters COMMUNICATION Hypertext Transfer Protocol Simple Object Access Protocol NAMING SYNCHRONIZATION CONSISTENCY AND REPLICATION Web Proxy Caching Replication for Web Hosting Systems Replication of Web Applications 579

10 CONTENTS xv 12.7 FAULT TOLERANCE SECURITY SUMMARY DISTRIBUTED COORDINATION-BASED 589 SYSTEMS 13.1 INTRODUCTION TO COORDINATION MODELS ARCHITECTURES Overall Approach Traditional Architectures Peer-to-Peer Architectures Mobility and Coordination PROCESSES COMMUNICATION Content-Based Routing Supporting Composite Subscriptions NAMING Describing Composite Events Matching Events and Subscriptions SYNCHRONIZATION CONSISTENCY AND REPLICATION Static Approaches Dynamic Replication FAULT TOLERANCE Reliable Publish-Subscribe Communication Fault Tolerance in Shared Dataspaces SECURITY Confidentiality Secure Shared Dataspaces SUMMARY 621

11 xvi CONTENTS 14 SUGGESTIONS FOR FURTHER READING 623 AND BIBLIOGRAPHY 14.1 SUGGESTIONS FOR FURTHER READING Introduction and General Works Architectures Processes Communication Naming Synchronization Consistency and Replication Fault Tolerance Security Distributed Object-Based Systems Distributed File Systems Distributed Web-Based Systems Distributed Coordination-Based Systems ,2 ALPHABETICAL BIBLIOGRAPHY 634 INDEX 669

Chapter 10 DISTRIBUTED OBJECT-BASED SYSTEMS

DISTRIBUTED SYSTEMS Principles and Paradigms Second Edition ANDREW S. TANENBAUM MAARTEN VAN STEEN Chapter 10 DISTRIBUTED OBJECT-BASED SYSTEMS Distributed Objects Figure 10-1. Common organization of a remote