Distributed and Cloud Computing Notes 1

Reasons for Distributed Systems

• Functional Separation
  • Different Capabilities and purposes
• Inherent Distribution
  • Information
  • People
• Power imbalance and load variation
• Reliability
• Economies

Consequences of Distributed Systems

• Concurrency - Each computer is autonomous
  • Carry our tasks independently
  • Tasks coordinate their actions by exchanging messages
  • System capacity can be increased by adding more resources
• No global clock
• Independent Failures

Motivation of Distributed Systems

• To share resource and information

Trends in Distributed Systems

• The emergence of pervasive networking technology
• The emergence of mobile and ubiquitous computing
• The increasing demand for multimedia services
• The view of distributed systems as a utility

Maintenance of intranet

• No rick if no connection to internet
• Firewalls are used to limit services from/to an intranet
  • Limit FTP/Remote Desktop etc.

Mobile computing: Performing computing tasks while the user is on the move, away from his/her usual environment

Eight forms of transparency

• Access transparency
• Location transparency
• Concurrency transparency
• Replication transparency
• Failure transparency
• Mobility transparency
• Performance transparency
• Scaling transparency

List of Challenge

• Heterogeneity
• Security
  • Confidentiality
    • Protection against disclosure to unauthorized individual information
  • Integrity
    • Protection against alteration or corruption
  • Availability
    • Protection against interference targeting access to the resources
    • DDoS
  • Authenticity or Non-repudiation
    • Proof of sending / receiving an information
    • digital signature

Failure

Availability =MTTF/(MTTF+MTTR)

• Mean time to failure(MTTF)
  • The average time of normal operation before the system fails
• Mean time to repair (MTTR)
  • The average time it takes to repair the system and restore it to working condition

Single point failure

Single hardware/Software component failures cause the whole system crash. The key approach to enhancing availability is to make as many as possible partial failures by removing single points of failure

Checkpointing

• The process of periodically saving the stage of an executing program to stable storage, from which the system can recover after a failure.
  • Each program stae saved is called a Checkpoint .
  • Checkpointing can be realized by operating system at kernel level/Third party library/by the application itself.

Jobs

• Serial Jobs: Run on a single node
• Parallel jobs: use multiple nodes
• Interactive jobs: require fast turnaround time, and their input/output is directed to a termainal
• Batch jobs: need more resources and don’t need immediate responses. Scheduled jobs.

job Management System

• A user server: Let user submit jobs.
• A job scheduler: performs job scheduling
• A resource manager: allocates and monitors resources. Enforces scheduling policies, and collects accounting information.

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Security Mechanisms

• Encryption(AES, RSA)
• Authentication(Password, Public key)
• Authorization(access control)

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• Concurrency
  • Fair scheduling
  • Preserve dependencies
  • Avoid deadlocks
  • Object locking, data consistency, semaphores
• Fault tolerance (No failure despite faults)
  • Fault detection
    • Checksums
    • Heartbeat
  • Fault masking
    • Retransmission of corrupted messages
    • Redundancy
  • Fault toleration
    • Exception handling
    • Timeouts
  • Fault recovery
    • Rollback mechanisms
• Scalability
• Openness
• Distribution transparency <= Do not let other touch