Introduction to Distributed Systems. Fabienne Boyer, LIG,

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1 Introduction to Distributed Systems Fabienne Boyer, LIG,

2 What is a distributed system? Set of software components Running in separate address spaces Communicating through a network Collaborating to a common goal A distributed system is one that stops you from getting any work done when a machine you ve never heard of crashes. Leslie Lamport Fabienne Boyer, Distributed Programming 2

3 What is a distributed system? Computer 1 Computer 2 Computer n Component Component Component 1 2 n Communication system Fabienne Boyer, Distributed Programming 3

4 Examples of distributed systems Information sharing Ø Wikipedia Distributed Games Collecticiels Ø Teleconference Ø Cooperative edition Ø Workflow (BPM) Real-time systems Ø Flying control systems Naming Servers Ø DNS Network File Servers Ø AFS, NFS Printing Servers Business Ø E-commerce Fabienne Boyer, Distributed Programming 4

5 Objectives of the course Study conceptual and practical aspects of distributed systems We will characterize a distributed system by Its properties Its architecture Its distributed protocol Its programming artefact Its execution model Fabienne Boyer, Distributed Programming 5

6 Expected properties of distributed systems Expected properties Main issues Availability Scalability Manageability Security Asynchronism Dynamicity Heterogeneity Size Fabienne Boyer, Distributed Programming 6

7 Characterization of distributed systems Distributed Programming Model Architecture Distributed Protocols Programming Artefacts Model Client-Server Synchronous Message Thread Multi-Tiers Asynchronous Procedure Process Peer-to-Peer Object Service Event Agent Fabienne Boyer, Distributed Programming 7

8 Architecture of distributed systems What software components (processes) form the system How are they connected What are their roles C1 C2 C4 C3 Fabienne Boyer, Distributed Programming 8

9 Client-Server architecture A client uses some services provided by a server Client Server Fabienne Boyer, Distributed Programming 9

10 Client-Server architecture General client-server distributed architecture Ø The server provides a service Ø A client may request that service The client and the server are usually hosted by two distinct machines machine 1 machine 2 1. request 2. processing client 3. response server communication link Fabienne Boyer, Distributed Programming 10

11 Client-Server architecture Request message Ø Sent by the client to the server Ø Specifies the requested service (a server may provide several services) Ø Contains parameters of the requested service Response message Ø Sent by the server to the client Ø Results of service execution, or error message Fabienne Boyer, Distributed Programming 11

12 Client-Server Contract 3 main aspects: Interface + Behavior + QoS The interface defines the format of the information exchanged between a service provider and its client Ø Ø IDL (Interface Definition Language) Examples: IDL Corba, Java interfaces, The behavior drives the exchanges between a service provider and its client Ø Example: session types (state charts) The QoS defines non-functional aspects Ø Atomicity, reliability (MTBF), execution time, price, security,.. Fabienne Boyer, Distributed Programming 12

13 Multi-tiers architecture The multi-tiers client-server architecture allows to parallelize client requests Server Client Server Server Server Fabienne Boyer, Distributed Programming 13

14 Peer-to-peer architecture Software components play the role of both clients and servers Client Client Client Client Fabienne Boyer, Distributed Programming 14

15 Distributed Programming Model The distributed programming model mainly determines What information is exchanged, From who to who, How it is exchanged, When it is exchanged How it is managed at sending and receiving times Fabienne Boyer, Distributed Programming 15

16 Distributed Programming Model What kind of information is exchanged Ø Data Ø Request (procedure call, object invocation) Ø Code Ø Object Ø Agent / Thread From who to who Ø Direct (process to process) Ø Indirect (exchanges go through a shared area) With what protocol Ø Synchronous (either blocking or non-blocking) Ø Asynchronous (generally non-blocking) Ø + Order, + reliability,+ atomicity Fabienne Boyer, Distributed Programming 16

17 Distributed protocol Ø Blocking o When the client sends a request, it waits until the server replies to its request Ø Non-blocking o A client does not wait for the result, it will be notified of (using client callbacks) Ø Synchronous o When the client (resp. server) sends a request (resp. a reply), the server (resp. client) should be running Ø Asynchronous o When the client (resp. server) sends a request (resp. a reply), the server (resp. client) may not be running Fabienne Boyer, Distributed Programming 17

18 Distributed protocol Ø Ordered (or not) o Requests are delivered to the server in the order they are sent to the client Ø Ø Reliable (or not) o No request lost Atomic (or not) o A request is either entirely executed at the server side, or not at all Fabienne Boyer, Distributed Programming 18

19 Distributed programming model Remote procedure call Computer 1 entity (process 1) Computer 2 entity (process 2) 2. procedure execution 1. request 3. Response Communication system Fabienne Boyer, Distributed Programming 19

20 Distributed programming model Remote method invocation Computer 1 entity (VM1) Computer 2 entity (VM2) 2. method execution 1. request 3. Response Communication system Fabienne Boyer, Distributed Programming 20

21 Distributed programming model Non-blocking procedure call or method invocation Computer 1 entity 1 Computer 2 entity 2 2. Procedure execution or method invocation 1. request Communication system Fabienne Boyer, Distributed Programming 21

22 Distributed programming model Event sending Computer 1 Computer 2 2. Callback entity 1 entity 2 1. event Communication system Fabienne Boyer, Distributed Programming 22

23 Distributed programming model Agents Computer 1 Computer 2 Agent Agent entity 1 execution entity 2 execution agent Communication system Fabienne Boyer, Distributed Programming 23

24 Distributed programming model Message queuing Computer 1 Computer 2 entity (process 1) entity (process 2) Message-oriented middleware (e.g. JMS) M4 M3 M2 M1 put put message a message M3 Communication system get a message Fabienne Boyer, Distributed Programming 24

25 Distributed programming model Distributed services Computer 2 Computer 1 entity 2 entity 1 Provide service Invoke Service Fabienne Boyer, Distributed Programming

26 Service-oriented distributed programming Base for service-oriented frameworks Ø A client specifies a required service Ø A server specifies a provided service Ø Static and/or dynamic matching between clients and servers A client does not have to identify a server, only a service Service orientation A service is a contractually defined behavior that can be implemented and provided by any component for use by any component, based solely on the contract. Bieber el. al., Service oriented programming, Fabienne Boyer, Distributed Programming 26

27 Distributed systems core layers Sockets (TCP, UDP) o o o Low-level protocol (based on messages) Allows for application-specific optimizations Data heterogeneity often managed by the application RPC (Remote procedure calls) o o Procedural programming Data heterogeneity managed by the application RMI (Remote Method Invocations) o o Object-oriented programming Data heterogeneity managed by the JVM Fabienne Boyer, Distributed Programming 27

28 Planning Séance Cours TD / TP 1 Introduction & Message-based distributed systems TCP Sockets 2 Asynchronous message-based distributed systems TCP Sockets 3 Asynchronous message-based distributed systems Java NIO 4 Object-based distributed systems Java NIO 5 Object-based distributed systems Java RMI 6 Asynchronous object-based distributed systems Java RMI Distribution projet Mobile agents 7.. Travail projet Mobile agents 8 Web protocols AAA 9 Service-oriented distributed systems Servlets 10 Evaluation projet Mobile agents Jini Fabienne Boyer, Distributed Programming 28

29 References Chris Britton, Peter Bye. IT Architectures and Middleware: Strategies for Building Large, Integrated Systems (2nd Edition). Addison-Wesley, George Coulouris, Jean Dollimore, Tim Kindberg. Distributed Systems: Concepts and Design (4th Edition). Addison Wesley, Arno Puder, Kay Römer, Frank Pilhofer. Distributed Systems Architecture: A Middleware Approach. Morgan Kaufmann, Andrew S. Tanenbaum, Maarten van Steen. Distributed Systems: Principles and Paradigms (2nd Edition). Prentice Hall, Fabienne Boyer, Distributed Programming 29

30 Distributed programming model Shared distributed objects Computer 1 Computer 2 entity 1 entity 2 Invoke object Shared objects store Fabienne Boyer, Distributed Programming