Enterprise Digital Infrastructure

Cloud vs fog computing

Cloud computing: it enables on-demand network access to a shared pool of computing resources that can be rapidly provisioned and released with minimal effort.

• Provisioning: requesting resources when needed.
• Releasing: releasing resources when not needed.

Fog Computing: the resources are closer to the user, so there's less latency. It's also called edge computing.

Cloud/compute continuum

Choice of the infrastructure

The choice will depend on:

• type of service or application: what is the system used for
• workload and traffic
• quality and performance requirements
• costs

There must be a balance of quality and cost. Sometimes over provisioning is performed, so the quality is higher than needed to satisfy future needs.

There can also be under provisioning to keep costs low.

Cloud vs fog computing

Cloud computing: it enables on-demand network access to a shared pool of computing resources that can be rapidly provisioned and released with minimal effort.

• Provisioning: requesting resources when needed.
• Releasing: releasing resources when not needed.

Fog computing: the resources are closer to the user, so there's less latency. It's also called edge computing.

Cloud/compute continuum

Choice of the infrastructure

The choice will depend on:

• type of service or application: what is the system used for
• workload and traffic
• quality and performance requirements
• costs

There must be a balance of quality and cost. Sometimes over provisioning is performed, so the quality is higher than needed to satisfy future needs. There can also be under provisioning to keep costs low.

Performance challenges

• On-demand services: it's hard to predict the user behavior, so it's also hard to predict what will be the maximum load.
• Popularity: the number of users vary over time due to external factors.
  • Network effect (psychological): user behavior is influenced by the behavior of other users, and will tend to be the same.
  • Flash crowd: it's a sudden increase of the number of requests of a service that lasts a short amount of time.
  • Slashdot effect: sudden increase of requests due to an event, such as a post made by a famous person.
• Location-based services: location data can be used to customize content. It might be difficult to predict where users will be located.
• Geographically distributed services.
• Composition of services under the control of multiple providers.

Requirements

• Functional requirements: technical properties (what the application does). These are tied to software engineering.
• Non-functional requirements: description of the behavior of a system and the experience of the users.
• NFR are usually represented by a Kiviat diagram; The area should be as big as possible.

Quality of Service (QoS)

It's a set of non-functional requirements that refer to the behavior of a service and the experience of its users.

• Dependability:
  • Availability (Uptime vs downtime)
  • Reliability (robustness of components)
  • Trustworthiness (security)
• Performance
• Usability
• Resiliency = robustness of a system or application. How it copes with unexpected conditions.

The perception of the attributes is subjective and depends on many factors. For example, users with low patience can be sensitive to response time. A long response time leads to frustration.

Usability

It measures the satisfaction of a user when interacting with a service. It is defined as the ability to learn and use a service and memorize it. It is a very subjective attribute, but it can be expressed in terms of:

• Efficiency = ability to complete a task easily, quickly and without frustration.
• Efficacy = ability to successfully complete a task.

Usability depends on (the UI and) the technological infrastructure and its performance.

Availability

It's the fraction of time during which a system is reachable and works properly.

Availability = ^uptime⁄_{uptime + downtime} = ^uptime⁄_T

Downtimes must be minimized. In the case of unscheduled downtimes, they must be managed carefully with well-timed announcements and following all the steps of the support route. Scheduled downtime must be well-planned and properly announced. Availability depends on human errors and external events, but also on the reliability of the technological infrastructure.

Incident example: Google

• Incident detection
• Investigate
• Mitigate
• Fix
• Postmortem