SLAC - SLA Calculator

A simple propositional logic probability calculator, with a typical senerio: calculate the theoretical SLA.

Model

Representation

The description model is simple and straightforward, without much abstraction, so it's expected to generate the cluster config by a script, but not write it by hand. It has five terms: Service, Infra, Connection, Program, Group.

• An Infra is a machine with predefined SLA.
• A Connection is a network connection with predefined SLA. According to your consideration, it could represent a connection between two machines, or a total connection plane.
• A Program is a running software on a Infra. It could depend on some Service through a Connection.
• A Service is abstract. It refers to an external service (with predefined SLA), or a group, a program.
• A Group is abstract. It represents the HA properbility of a some program. A Group is considered unavailable iff the number of available program is less than the minReplia.

Represent your service with these five terms, the slac can help you to calculate the theoretical SLA, with the assumption that your custom program is 100% reliable.

Calculation

We can represent the event "Service A is available" by the intersect or union of "X is available", where X is with predefined SLA.

With the assumption that "X is available" (where X is with predefined SLA) is independent, we can calculate the final SLA.

TODO

• Provide a easy to use cluster/application abstraction
• Calculate the credit and multiple-steps SLA
• Support per-minute SLA model
• Consider the dependency of down minutes
• Illustrate the affect of an error, and lead the user to verify this hyponsis through Chaos Mesh.
• Support dependent event.