Design Issues or Challenges

• Heterogeneity
• Openness
• Security
• Scalability
• Failure handling
• Concurrency
• Transparency

Heterogeneity

• Different networks, hardware, operating systems, programming languages, developers.
• We set heterogeneities.
• Middleware: a software layer that provides a programming abstraction as well as masking the heterogeneity.
• Mobile code: code that can be sent from one computer to another and run at the destination. up protocols to solve these

Openness

• DS is determined primarily by the openness degree to which new resource-sharing services can be added and be made available for use by a variety of client programs.
• Open systems are characterized by the fact that their key interfaces are published.
• Open DS are based on the provision of a uniform published interfaces for access to shared communication mechanism and resources.
• Open DS can be constrcted from heterogeneous hardware and software.

Security

• Security for information resources has three components:
  • Confidentiality: protection against disclosure to unauthorized individuals.
  • Integrity: protection against alteration or corruption.
  • Availability: protection against interference with the means to access the resources.
• Two new security challenges:
  • Denial of service attacks (DoS).
  • Security of mobile code.

Scalability

• A system is described as scalable if it remains effective when there is a significant increase in the number of resources and the number of users.
• Challenges:
  • Controlling the cost of resources or money.
  • Controlling the performance loss.
  • Preventing software resources from running out
  • Avoiding preformance bottlenecks.

Failure handling

• When faults occur in hardware or software, programs may produce incorrect results or they may stop before they have completed the intended computation. -Techniques for dealing with failures:
  • Detecting failures
  • Masking failures
  • Tolerating failures
  • Recovering form failures
  • Redundancy

Concurrency

• There is a possibility that several clients will attempt to access a shared resource at the same time.
• ANY object that represents a shared resource in a distributed system must be responsible for ensuring that operates correctly in a concurrent environment.

Transparency

• Transparency is defined as the concealment from the user and the application programmer of the separation of components in a distributed system, so that the system is perceived as a whole rather than as a collection of independent components.
• Eight forms of transparency:
  • Access transparency
  • Location transparency
  • Concurrency transparency
  • Replication transparency
  • Failure transparency
  • Mobility transparency
  • Performance transparency
  • Scaling transparency