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Prof. Leonardo Mostarda University of Camerino

Explore the world of distributed systems with this comprehensive guide covering architectures, processes, communication, security, and more. Understand the importance of sharing, transparency, openness, and scalability in distributed systems.

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Prof. Leonardo Mostarda University of Camerino

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  1. Distributed Systems – intro Prof. Leonardo Mostarda University of Camerino Prof. Leonardo Mostarda-- Camerino,

  2. Who am I? • Prof. Leonardo Mostarda • Born in Poggio Bustone • Lived for the last 8 years in London

  3. Who am I? • Degree + Ph.D. at University of L’Aquila • Cooperating with the Ericsson research lab. • Consultancy: Fiat, Ericson, Nokia, … • Post Doc European Space Agency (ESA): • GALELEO satellite system applied to security • Research associate: Imperial College London • Ubival project with Oxford and Cambridge • Prof. Middlesex University London • My research interests: Security, Distributed Systems and wireless sensor networks • HP and IBM research labs and INRIA are using my system

  4. Module Outline (provisional) • INTRODUCTION • 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

  5. Activity Plans

  6. Outline • Basic definitions • Goals when implementing a distributed system • Sharing • Transparency • Openness • Scalability • Scalability techniques

  7. Definition of a Distributed System: “A collection of independent computers that appears to its users as a single coherent system.” Tanenbaum & Van Steen. “A distributed system is one in which the failure of a computer you didn't even know existed can render your own computer unusable”Leslie Lamport “A distributed system is an application that executes a collection of protocols to coordinate the actions of multiple processes on a network, such that all components cooperate together to perform a single or small set of related tasks.” Google University Code

  8. Definition of a Distributed System A distributed system is organised as a middleware. The middleware layer extends over multiple machines and offer each application the same interface.

  9. Goals • 4 goals you should met to make the implementation of a distributed system worth: • Sharing • Transparency • Openness • Scalability Prof. Leonardo Mostarda-- Camerino,

  10. Sharing • Users should be able to access easily remote resources • Cost effective: • it is cheaper to share a printer instead of buying one for each user. • Costly resources such as supercomputers and high performance storage systems should be shared • Easier to collaborate: • Mail, file sharing, Groupware software

  11. Sharing SECURITY? Do you see any disadvantages in sharing?

  12. Sharing Is a stand alone computer secure?

  13. Transparency in a Distributed System A transparent distributed system presents itself to users and applications as if it were running on a single computer. We need to hide where the processes and resources are physically distributed across multiple computers Let us have a look what kinds of transparency we have and whether is always required.

  14. Transparency in a Distributed System Different forms of transparency in a distributed systems (ISO,1995)

  15. Degree of Transparency • Communication delays • Replicas updating • Masking a transient server failure Can we always achieve a high degree of transparency?

  16. Openness • In an open distributed systems service are specified according to standard rules that describe both syntax and semantic. • Interface Description Language (IDL) for syntax • Natural language for semantic • Specifications should be complete and neutral in order to allow Interoperability and Portability • flexibility is also important that is how easy is to add and replace components Prof. Leonardo Mostarda-- Camerino,

  17. Scalability “A distributed system is scalable when it improves is performance after adding resources” “Scalability is the ability of a system, network, or process, to handle growing amounts of work in a graceful manner or its ability to be enlarged to accommodate that growth” Scalability is very hard to achieve

  18. Scalability Problems DNS

  19. Scaling Techniques (1): hiding communication The difference between letting (a) a server or (b) a client check forms as they are being filled.

  20. Scaling Techniques (2): distribution An example of dividing the DNS name space into zones.

  21. Scaling Techniques (3): replication Any problem? Inconsistency Cache Replica

  22. Checking the learning outcomes • Define a distributed systems • Define • Sharing • Transparency • Openness • Scalability • What is the difference between caching and replica?

  23. Summary • Basic definitions • Goals when implementing a distributed system • Sharing • Transparency • Openness • Scalability • Scalability techniques

  24. Questions? Prof. Leonardo Mostarda-- Camerino,

  25. 15 minutes pause Prof. Leonardo Mostarda-- Camerino,

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