Notes - MIECT
Computação Distribuída
Notes - MIECT
Computação Distribuída
  • Computação Distribuída
  • Introduction / Architecture
    • Distributed Systems
    • Architecture
    • Middleware Organizations
    • Processes
    • Threads
    • Virtualization
    • Clients
    • Servers
    • Migration
  • Communications
    • OSI Model
    • Middleware Layer
    • Types of Communication
    • Remote Call Procedure (RPC)
    • Sockets
    • Application-level Multicasting
  • Naming
    • Names
    • Addresses
    • Identifiers
    • Naming Systems
      • Flat Naming
      • Structured Naming
    • Internet Domain Name System (DNS)
    • Attribute-based naming - LDAP
  • Coordination
    • Clocks
      • Synchronizing without UTC
    • Reference Broadcast Synchronization – RBS
    • Happened-Before Relation
      • Logical Clocks
      • Vector Clocks
    • Mutual Exclusion Algorithms
    • Election Algorithms
    • Distributed Events Correspondance
  • Consistency & Replication
    • Replication
    • Performance and Scalability
    • Client-centric models
    • Replicates
    • Unicasting vs. Multicasting
    • Continuous Consistency
    • Protocols
  • Flaw Tolerance
    • Dependability
    • Terminology
    • Confidence vs. Security
    • Halting failures
    • Redundancy to mask failures
    • Consensus
      • Realistic
      • Consensus in arbitrary failures
      • Achieving failure tolerance
      • Distributed consensus
    • Failure Detection
    • Reliable RPCs
    • Distributed commit protocols
  • Python asyncio & Friends
    • Async
    • Sync vs. Async
    • Tools
  • Flask
    • Introduction
    • Python Requests
  • Containers
    • VM's vs Containers
    • OS Support
    • Building a container
    • Tools
    • Portability
    • Docker
      • Container
  • Map Reduce
    • Map Recude
    • Hadoop
    • Software Architecture
    • Task Scheduling
    • Comparison With Traditional Models
  • Cloud Computing
    • Cloud Computing
    • IaaS – Infrastructure as a Service
    • PaaS – Platform as a Service
    • SaaS – Software as a Service
    • Business Models
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  1. Flaw Tolerance

Dependability

PreviousProtocolsNextTerminology

Last updated 2 years ago

A component makes available services to its clients. So it can make them available, the component may need services from other components -> one component may depend on another component.

Component C depends on C' if the correctness of C depends on the correctness of C'.

Requirement
Description

Availability

Readiness to be used.

Dependability

Continuous availability of a service.

Security

Low catastrophy probability.

Maintenance

How easy it is to repair the system.

Reliability vs. Availability

Reliability R(t) of component C.

  • The conditional probability that C is working correctly during [0,t[ knowing that C was working correctly at t=0.

Additional metrics:

  • Mean Time To Failure (MTTF): Average time until a component fails.

  • Mean Time To Repair (MTTR): Average time necessary to repair a component.

  • Mean Time Between Failures (MTBF): MTTF + MTTR

Availability D(t) of component C.

  • Average fraction of time between [0,t[ when C has been working.

  • Long-term availability D: D(∞).

  • D = MTTF / MTBF = MTTF / (MTTF + MTTR)

Talking about reliability and availability only makes sense when we have a clear notion of what is a failure.