Learning term
Horizontal scaling — Reliability and capacity planning
Horizontal scaling changes the number of equivalent instances and requires shareable state. This card shows its role in “Reliability and capacity planning” and a safe diagnostic path.
Orientation
Horizontal scaling changes the number of equivalent instances and requires shareable state. At this level, separate purpose, input, and visible result. Place Horizontal scaling within Reliability and capacity planning before changing settings or files.
Practical use
Wait time rises sharply during two concurrent jobs. For Horizontal scaling, measure arrival rate, queue length, runtime, and resource peak; bound the test load and verify that the chosen capacity or protection rule produces the expected behavior. Start in a sandbox with neutral examples. Record the expected state, make one controlled change, and compare status output, application behavior, and logs.
Technical understanding
Horizontal scaling changes the number of equivalent instances and requires shareable state. Technically, Horizontal scaling connects through interfaces, configuration, state, or dependencies. Trace data from input to output and check versions, permissions, networking, storage, and resources separately.
Operations and debugging
Wait time rises sharply during two concurrent jobs. For Horizontal scaling, measure arrival rate, queue length, runtime, and resource peak; bound the test load and verify that the chosen capacity or protection rule produces the expected behavior. In production-like operations, use measurable signals, least privilege, reproducible configuration, and a documented rollback. Preserve evidence, isolate the cause, and verify the correction with the same test.
Exercise
Try it safely
Wait time rises sharply during two concurrent jobs. For Horizontal scaling, measure arrival rate, queue length, runtime, and resource peak; bound the test load and verify that the chosen capacity or protection rule produces the expected behavior. Open an isolated test environment and run “docker stats --no-stream”. Write down the expected output first, do not alter production data, and record one safe next diagnostic step.
docker stats --no-streamQuick check
Can you explain the purpose, observable state, and most common failure source of Horizontal scaling — Reliability and capacity planning in one sentence each? Which evidence would you preserve before changing anything, and which repeated test would prove that the correction actually worked?