Requirements Definitions

Availability

• percentage of the time where server is online and functioning
• measured in number of 9s e.g. 99.9% available
• Service Level Objective (SLO) - mainly on availability and reliability
• Service Level Agreement (SLA) - consequence if the object is not achieved, such as AWS cannot ensure availability of their service
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Reliability, Fault Tolerance and Redundancy

• Reliability - Probability that the system won't fail
  • DOS (Denial of Service attack)
• Fault Tolerance - Incase on server is down, other server can still carry computation and action
• Redundancy - Extra resource such as a server
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Through put

• Amount of information the server can handle over period of time
• request per second or byte per second
• for databases - queries per second
• single point of failure - no horizontal scaling

Latency

• amount of time does the entire operation take
• how long does each request take
• CDN - content delivery network

Scalability

• ability for server to handle increased work load without compromise performance
  • Request workload
  • database workload
• Dimension
  • Size scalability: A system is scalable in size if we can simply add additional users and resources to it.
  • Administrative scalability: This is the capacity for a growing number of organizations or users to share a single distributed system with ease.
  • Geographical scalability: This relates to how easily the program can cater to other regions while maintaining acceptable performance constraints. In other words, the system can readily service a broad geographical region, as well as a smaller one.

Maintainability

• the probability that the service will restore its functions within a specified time of fault occurrence

  1. Operability: This is the ease with which we can ensure the system’s smooth operational running under normal circumstances and achieve normal conditions under a fault.
  2. Lucidity: This refers to the simplicity of the code. The simpler the code base, the easier it is to understand and maintain it, and vice versa.
  3. Modifiability: This is the capability of the system to integrate modified, new, and unforeseen features without any hassle.

• Move Data

  • from one machine to another

• Store Data

  • Database
  • Blob store

• Transform Data

  • Transform log, distill useful informations