DevOps Principles
What this domain covers
DevOps Principles tests the mental models behind the practices: the Three Ways, CALMS, systems thinking, flow, feedback and continual learning. Expect questions that ask which principle a scenario illustrates, or which metric is consistent with a principle.
The Three Ways
- Flow. Accelerate work from development to operations and the customer. Make work visible, reduce batch sizes, limit work in progress, remove waste and never pass a known defect downstream.
- Feedback. Amplify fast, right-to-left signals from production and customers. Telemetry, automated tests, stop-the-line behavior and swarming on incidents are feedback mechanisms.
- Continual learning and experimentation. Treat failure as information. Use blameless postmortems, deliberate experimentation and practice to build capability.
CALMS
CALMS is a diagnostic checklist: Culture (trust, shared ownership, blameless learning), Automation (repeatable work), Lean (small batches, value stream, flow), Measurement (metrics that inform decisions) and Sharing (knowledge, tools and failures). It is not a maturity ladder; a team can be strong in one area and weak in another.
Systems thinking
Optimize the whole value stream, not a single silo. A busy development team can harm flow by creating inventory. Local efficiency is not global throughput; improve the bottleneck first.
Worked example
A team raises unit-test coverage from 30% to 80%, but lead time is unchanged. Applying the principles: the tests run only in a nightly job, so feedback arrives too late, and a shared test environment is the constraint. The principle-led fix is to run fast tests on every merge and relieve the environment bottleneck, not to chase 100% coverage. Reasoning: coverage is a local metric; flow and feedback are system properties.
Traps that cost marks
- Treating the Three Ways as sequential project phases; they are concurrent principles.
- Reading blameless as no accountability.
- Using utilization as a target; high utilization lengthens queues.
- Calling a social event culture instead of changing ownership and behavior.