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Key Design Issues in Internet Servers: Functionality, Robustness, and Fault Tolerance

This lecture discusses essential design issues related to Internet servers, focusing on their functionality and ability to handle multiple concurrent clients. Key topics include maintaining client-specific state, reducing message sizes, ensuring fault tolerance, and implementing access control and data security. The discussion covers server socket calls, connection handling, and the importance of idempotent operations in a stateful server environment. The lecture emphasizes the need for robust servers to provide enhanced functionality while navigating the challenges of client reliability and network failures.

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Key Design Issues in Internet Servers: Functionality, Robustness, and Fault Tolerance

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  1. Internet and Intranet Protocols and Applications Lecture 4: Internet Servers Feb 15, 2000 Arthur P. Goldberg Clinical Associate Professor of Computer Science and Information Systems New York University artg@cs.nyu.edu

  2. Server design issues • Functionality • Handle multiple clients concurrently • Maintaining client-specific state at a server (usually) • Reduce message sizes • Require fault-tolerance • Access control • Authenticate clients • Evaluate whether client is allowed access • Secure data • Robustness • Performance • Reliability

  3. Server Socket Calls rc = bind(socket,(struct sockaddr *) localaddr, addrlen); • Specify local IP:port rc = listen(socket, queuelen); • TELL socket to queue up to queuelen REQUEST retcode=accept(socket, (struct sockaddr*) addr, (int *)addrlen); • wait until connection REQUEST arrives; return descriptor of new connected socket. [datatypes int unless otherwise specified]

  4. Fork rc=fork(); • duplicate process; return 0 to child, child PID to parent.

  5. Select #include <sys/types.h> #include <sys/time.h> int select (width, readfds, writefds, exceptfds, timeout); int width; fd_set *readfds, *writefds, *exceptfds; struct timeval *timeout; • wait for first fd in a set to become ready, or a timeout.

  6. Precise description of stateful server challenge • Idempotent • An operation which can be applied multiple times and still produce the same result • Formally, operation O is idempotent iff • O( a ) = O( O( a ) ) • Example • Idempotent: x = z • Not idempotent: x = x +z • In a stateful server • Request operations must be idempotent, or • The server must recover from failures

  7. Comer advice • If the network is unreliable or machines can crash then the server should be stateless • I disagree: I think we need to make stateful servers, because they provide greater functionality; therefore, they must be fault-tolerant

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