1	Modulo I Introdução aos Sistemas Distribuídos Prof. Ismael H F Santos
2	Bibliografia Sistemas Distribuídos Santos,F., H., Ismael; Notas de Aula, 2005 Sistemas Operacionais e Programação Concorrente Toscani e outros, Editora sagra-luzzatto Fundamentos de Sistemas Operacionais Silberschatz, Abraham, Galvin, Peter, Gagne, G., LTC Sistemas Distribuídos Andrew S. Tanenbaun; Prentice Hall Operating System Concepts: Internals and Design Principles Williiam Stallings, Prentice Hall
3	Ementa Distributed Systems Hardware for Distibuted Systems Client Server Paradigm Networking Client Server Communication
4	SOA
5	Motivation Distributed system is collection of loosely coupled processors interconnected by a communications network Processors called nodes, computers, machines, hosts Site is location of the processor Reasons for distributed systems Resource sharing sharing and printing files at remote sites processing information in a distributed database using remote specialized hardware devices Computation speedup – load sharing Reliability – detect and recover from site failure, function transfer, reintegrate failed site Communication – message passing
6	A Distributed System
7	Definition of a Distributed System (2)
8	Transparency in a Distributed System
9	Multitiered Architectures (1) Alternative client-server organizations (a) – (e).
10	Multitiered Architectures (2) An example of a server acting as a client.
11	Scalability Problems
12	Scaling Techniques (1)
13	Scaling Techniques (2)
14	Types of Distributed Operating Systems Network Operating Systems Distributed Operating Systems
15	Network-Operating Systems Users are aware of multiplicity of machines. Access to resources of various machines is done explicitly by: Remote logging into the appropriate remote machine (telnet, ssh) Transferring data from remote machines to local machines, via the File Transfer Protocol (FTP) mechanism
16	Distributed-Operating Systems Users not aware of multiplicity of machines Access to remote resources similar to access to local resources Data Migration – transfer data by transferring entire file, or transferring only those portions of the file necessary for the immediate task Computation Migration – transfer the computation, rather than the data, across the system
17	Distributed-Operating Systems (Cont.) Process Migration – execute an entire process, or parts of it, at different sites Load balancing – distribute processes across network to even the workload Computation speedup – subprocesses can run concurrently on different sites Hardware preference – process execution may require specialized processor Software preference – required software may be available at only a particular site Data access – run process remotely, rather than transfer all data locally
18	Network Structure Local-Area Network (LAN) – designed to cover small geographical area. Multiaccess bus, ring, or star network Speed » 10 megabits/second, or higher Broadcast is fast and cheap Nodes: usually workstations and/or personal computers a few (usually one or two) mainframes
19	Depiction of typical LAN
20	Network Types (Cont.) Wide-Area Network (WAN) – links geographically separated sites Point-to-point connections over long-haul lines (often leased from a phone company) Speed » 100 kilobits/second Broadcast usually requires multiple messages Nodes: usually a high percentage of mainframes
21	Communication Processors in a Wide-Area Network
22	SOA
23	Hardware Concepts
24	Multiprocessors (1)
25	Software Concepts DOS (Distributed Operating Systems) NOS (Network Operating Systems) Middleware
26	Uniprocessor Operating Systems Separating applications from operating system code through a microkernel.
27	Multicomputer Operating Systems (1) General structure of a distributed system as middleware.
28	Multicomputer Operating Systems (2) Alternatives for blocking and buffering in message passing.
29	Multicomputer Operating Systems (3) Relation between blocking, buffering, and reliable communications.
30	Distributed Shared Memory Systems (1) Pages of address space distributed among four machines Situation after CPU 1 references page 10 Situation if page 10 is read only and replication is used
31	Distributed Shared Memory Systems (2) False sharing of a page between two independent processes.
32	Network Operating System (1) General structure of a network operating system.
33	Network Operating System (2) Two clients and a server in a network operating system.
34	Network Operating System (3) Different clients may mount the servers in different places.
35	Middleware and Openness In an open middleware-based distributed system, the protocols used by each middleware layer should be the same, as well as the interfaces they offer to applications.
36	Middleware and Openness In an open middleware-based distributed system, the protocols used by each middleware layer should be the same, as well as the interfaces they offer to applications.
37	Modern Architectures An example of horizontal distribution of a Web service.
38	Comparison between Systems A comparison between multiprocessor operating systems, multicomputer operating systems, network operating systems, and middleware based distributed systems.
39	SOA
40	Software and hardware service layers in distributed systems
41	Clients invoke individual servers
42	A service provided by multiple servers
43	Web proxy server
44	A distributed application based on peer processes
45	Web applets
46	Thin clients and compute servers
47	Spontaneous networking in a hotel
48	Real-time ordering of events
49	Processes and channels
50	SOA
51	Middleware layers
52	Client-Server Communication Sockets Remote Procedure Calls Remote Method Invocation (Java) CORBA Object Registration
53	Middleware layers
54	Sockets A socket is defined as an endpoint for communication Concatenation of IP address and port The socket 161.25.19.8:1625 refers to port 1625 on host 161.25.19.8 Communication consists between a pair of sockets All Ports < 1024 are Considered “well-known” - TELNET uses port 23 - FTP uses port 21 - HTTP server uses port 80
55	Socket Communication
56	Sockets and ports
57	Java Sockets Java Provides: - Connection-Oriented (TCP) Sockets - Connection-less (UDP) Sockets - Multicast Connection-less Socket
58	Time-Of-Day Server/Client Server uses ServerSocket to Create the Socket on Port 5155 ServerSocket s = new ServerSocket(5155); To Accept Connections From Clients: Socket client = s.accept(); Connections are Often Serviced in Separate Threads The Client Connects to the Server Using Socket class with the IP Address of the Server. Socket s = new Socket(“127.0.0.1”,5155);
59	Sockets used for streams
60	Client and server with threads
61	TCP client makes connection to server, sends request and receives reply
62	TCP server continued
63	An Example Client and Server (1) The header.h file used by the client and server.
64	An Example Client and Server (2) A sample server.
65	An Example Client and Server (3) A client using the server to copy a file.
66	Alternative server threading architectures
67	State associated with execution environments and threads
68	Java thread constructor and management methods
69	Java thread synchronization calls
70	Sockets used for datagrams
71	UDP client sends a message to the server and gets a reply
72	UDP server repeatedly receives a request and sends it back to the client
73	TCP server makes a connection for each client and then echoes the client’s request
74	Multicast peer joins a group and sends and receives datagrams
75	Multicast peer continued …
76	Indication of Java serialized form
77	Representation of a remote object reference
78	Remote Procedure Calls Sockets are Considered Low-level. RPCs Offer a higher-level Form of Communication Client Makes Procedure Call to “Remote” Server Using Ordinary Procedure Call Mechanisms. Remote procedure call (RPC) abstracts procedure calls between processes on networked systems.
79	Remote Procedure Calls Remote procedure call, RPC Stubs – client-side proxy for the actual procedure on the server. The client-side stub locates the server and marshalls the parameters. The server-side stub receives this message, unpacks the marshalled parameters, and peforms the procedure on the server.
80	Stubs and Skeletons “Stub” is a Proxy for the Remote Object – Resides on Client. The Stub “Marshalls” the Parameters and Sends Them to the Server. “Skeleton” is on Server Side. Skeleton “Unmarshalls” the Parameters and Delivers Them to the Server.
81	Remote Method Invocation Remote Method Invocation (RMI) is a Java mechanism similar to RPCs. RMI allows a Java program on one machine to invoke a method on a remote object.
82	Remote Method Invocation A Thread May Invoke a Method on a Remote Object An Object is Considered “remote” if it Resides in a Separate Java Virtual Machine.
83	A remote object and its remote interface
84	The role of proxy and skeleton in remote method invocation
85	Marshalling Parameters
86	Role of client and server stub procedures in RPC
87	RPC versus RMI RPC’s Support Procedural Programming Style RMI Supports Object-Oriented Programming Style Parameters to RPCs are Ordinary Data Structures Parameters to RMI are Objects
88	Classes supporting Java RMI
89	Parameters Local (Non-Remote) Objects are Passed by Copy using Object Serialization Remote Objects are Passed by Reference
90	Remote Objects Remote Objects are Declared by Specifying an interface that extends java.rmi.Remote Every Method Must Throw java.rmi.RemoteException
91	MessageQueue interface import java.rmi.*; public interface MessageQueue extends Remote { public void send(Object item) throws RemoteException; public Object receive() throws RemoteException; }
92	MessageQueue implementation import java.rmi.; public class MessageQueueIMPL extends server.UnicastRemoteObject implements MessageQueue { public void send(Object item) throws RemoteException { / implementation / } public Object receive() throws RemoteException { / implementation */ } }
93	The Client The Client Must (1) Install a Security Manager: System.setSecurityManager( new RMISecurityManager()); (2) Get a Reference to the Remote Object MessageQueue mb; mb = (MessageQueue)Naming.lookup( “rmi://127.0.0.1/MessageServer”’);
94	Running the Producer-Consumer Using RMI Compile All Source Files and Generate Stubs javac *.java; rmic MessageQueueImpl Start the Registry Service rmiregistry Create the Remote Object java –Djava.security.policy=java.policy MessageQueueImpl Start the Client java –Djava.security.policy=java.policy Factory
95	Policy File New with Java 2 grant { permission java.net.SocketPermission "*:1024-65535","connect,accept"; };
96	Java Remote interfaces Shape and ShapeList
97	The Naming class of Java RMIregistry
98	Java class ShapeListServer with main method
99	Java class ShapeListServant implements interface ShapeList
100	Java client of ShapeList
101	CORBA RMI is Java-to-Java Technology CORBA is Middleware that Allows Heterogeneous Client and Server Applications to Communicate Interface Definition Language (IDL) is a Generic Way to Describe an Interface to a Service a Remote Object Provides Object Request Broker (ORB) Allows Client and Server to Communicate through IDL. Internet InterORB Protocol (IIOP) is a Protocol Specifying how the ORBs can Communicate.
102	Corba Model
103	CORBA IDL example
104	Registration Services Registration Service Allows Remote Objects to “register” their services. RMI, CORBA Require Registration Services
105	System layers
106	Core OS functionality
107	Address space
108	Copy-on-write
109	Request-reply communication
110	Operations of the request-reply protocol
111	Request-reply message structure
112	RPC exchange protocols