Reliability Metrics

Motivation

Measurements that quantify service continuity, failure frequency, and recovery performance.

Where it fits

This concept provides a shared vocabulary for designing, documenting, measuring, or operating software systems.

Mental model

Treat it as a structured tool: define the question being answered, use consistent terminology, and connect the result to decisions and follow-up work.

Subconcepts

Uptime

The amount or percentage of time a service is operating.

Availability Targets

Targets such as 99.9% or 99.99% defining permitted downtime.

Error Rate

The proportion of operations that fail or produce invalid outcomes.

Failed Requests

The count or rate of requests that do not complete successfully.

Recovery Time

The elapsed time required to restore acceptable service after failure.

MTTR

The average time required to recover or repair after incidents.

MTBF

The average operating time between failures.

Practical use

Reliability measurements must specify event definitions, measurement windows, exclusions, and whether planned maintenance is included.

Common mistakes

• Using ambiguous definitions or units.
• Collecting or documenting information without connecting it to a decision.
• Failing to keep the artifact or measurement current as the system changes.

Related concepts

See the linked concepts in the knowledge graph for prerequisites and adjacent practices.